m4 ’ fit . . wd' WIN ~ t ' - a L35“? p % M'w-*;a-/| ‘44. } -"v‘;~"~~‘__/ 5. L xx. V. V‘ .1 .3 .l E C 1 T C C. .u _ . r. T. C .L m n . . E C :. .... +» .u .. .... .2 R .w .u :— s .¢ .fi A r .3 a. L. t ‘ 1 «D . ‘ p: 1» ~ .. ufiu ~ ‘- . v w. .L 5 i; 2. my o «b T. u. ..L a L N. i s L x; I C a 2 .s s C u I . .. .2 Q» “U. ‘6 ABSTRACT THE DEVELOPMENT AND TESTING OF AN INSTRUCTIONAL MODEL FOR LABORATORY EXPERIMENTS ON ELECTRONIC CIRCUITS IN COLLEGE-LEVEL ENGINEERING BY Shlomo Waks The purpose of this study was to create an instruc— tional model which would improve a student's understanding of the Operation and application of electronic circuits, and to increase his laboratory skills through the use of a systematic approach involving audio-tutorial techniques. A model for laboratory experiments on electronic circuits was suggested for implementing this systematic approach. There are eleven main components of the model developed: 1. Preliminary work by a student based on handouts and assigned reading, including calculations of electrical performance that will be measured in the laboratory experi- mentation. 2. Use of audio—tutorial techniques in the theoreti- cal analysis of the circuit and its applications. 3. Use of an oscillosc0pe as a powerful medium in studying electronic circuits for scanning the output char— acteristics, displaying waveshapes at various points in ... ..y..... . .u: voov-I- I I " "a “-r v. v.cv U ‘ Q-r .. . .R: .u. p... ' w..- r" 1‘:— “-vv.. . - A ‘ r. d‘ \g‘ .u... ' _ v-g b- '_ .All'-‘_. .. "wb .“ ‘V. ‘ D s. \- -.. ‘.. . -.::-'_‘ QA‘ --~'-.._ '-' d va.‘.""~~._ ‘b‘ll."':‘ "p—-_‘.- . _) H u..." '- .:'.' u ‘ . —vv~..,~~ - :."‘-L‘ w I: mm.“ 0‘. ‘..'»-. F .. U. U. ”A.‘ _-~'V - .H.‘:IVH~.A ‘— ‘w. x... ’5‘ - h.u.~: Pu.,‘ ‘ h“ - V“‘ w ~ 1. _ -I . .- :A~““ s... 2 's..‘ n ‘ . b ‘H- . I“: C‘ -§ . ‘M .. A Q ‘Q Kb ~V:0~’N f‘ ‘ ‘I‘ V CF‘,‘~ ‘u" n ‘V ~r~ . .~‘ ‘ 'v‘~ .: ‘“ N “‘1‘: r: .V‘ . ~ ‘. s: '“».A a“ M“ ‘\ x Q " U. Q A.. ”VA" “ 3 ¢ 4 :s 11‘ ‘ s k...‘ s. n ‘b c \ ‘ii. ~ I; CV ~ ’ Q» ‘ \ a_ K Shlomo Waks the circuit, or scanning the actual transfer characteristic of the circuit; that is, the output voltage as a function of the input voltage. 4. Use of guides and flow charts describing the experi- ment procedure (Optional). 5. Creation of conditions for a student's active involvement in the experimenting process--letting him take part in the "design" of the circuit by calculating some missing components and providing immediate feedback for reinforcement. Measuring the circuit operation and getting expected results during the experimental process frequently provides a student with successful experience; this increases his involvement. 6. D.C. (Direct Current) and A.C. (Alternating Current) measurements of the Circuit's operation and comparison to precalculated values of voltage, current, or amplification. 7. The use of an eXperimental analysis of the circuit; a combination of laboratory and theoretical investigation of the Circuit's reaction to external or internal changes imposed on it, like changing feeding voltages, loading, environmental circumstances (temperature), or changing the values of its internal components. If an integrated circuit is under experiment, only external changes are investigated. 8. To keep in touch with the real world, a student is shown a few typical practical applications of the circuit at this stage; the newly learned details of the circuit are investigated under real conditions. It is recommended that (I! ‘1 ~ ay-Qo- A: ‘ ‘ ~-.¢uu-vu- u A n_ j. \w» . . A~~~~cn gm.- . u:~-vnn «a» “'F‘V'U- Q Ua‘vd-' -.. ‘r-v:>. .’ V'».‘~-v... n .. *' -'. ..-_ . ‘u-‘A f 3' (D . ~ hfifi" ‘ » ““- r .— ~‘~ ‘- .. N ._.5: PE“— “-uer . ~2~ - ‘.‘E C~.__ V“'~;-Y s V‘ A ‘x". . ~- “- t ... -D ”A b. V h ~"w3 4 ~‘ ‘er. - V ‘o h- t.. Q . 5*. 5.. I. Shlomo Waks media be utilized for application demonstrations if "live" practical circuits are unavailable. 9. College-level students are asked at this stage to design adequate modifications to be introduced into the circuit in order to satisfy newly imposed conditions of Operation. 10. The posttest in any format (oral, written, perfor— mance, or in a combination of the three testing forms) is to be taken right after the experiment procedure. 11. The modular structure of the model enables its use at different levels (i.e., engineering, community college, technical school). The model was applied to the "Electronic Devices Laboratory" E.E. 484 (senior level) in the College of Elec— trical Engineering at Michigan State University during Fall Term, 1972. A total of 108 students nuns divided into ten lab sections. Five of the sections (treatment groups) used the suggested model to perform their lab experiment: The Schmitt Trigger——Theory and Applications. This lab experi- ment was scheduled to last two weeks, for three hours weekly. The other five sections, comparison groups, performed the same experiment under the traditional method of experimenta- tion. The treatment groups had three instructors, and the comparison groups had two other instructors. The following items were prepared to be used in the Schmitt circuit experiment: r _ .: .: n: u. .. .3 ... 3 . 3 .: .u v. S ... .. . . C 2 .. M .n. — rub o p . . “ rub Q A . Q 5» ‘. v. ‘fim :. I. a .2 A. A. .2 u I. n . .L. .. 3. ... w; . . 3 .x. .3 .3 I 2. u. I ... Ow . ‘ u u Q J. i. .3 .2 1‘ .2 2. .0 cu 2. ..u u. an u” In 1‘ o. . u L. . g In O.‘ .u H 00-9..- .— b .3 Ln... Cs C§ '.. ~. by :~ . a a 3. an n .2 a ... .... O. u~ A. ~\- .u 1. nu .- o. .s as» ‘3. A "‘C Shlomo Waks 1. Theory Sheets, including the Schmitt circuit theory and applications. 2. Experimental Procedure Sheets. 3. A slide-tape presentation of the Schmitt analysis and applications. The experiment was evaluated by four tests: a pre— test, a posttest, a retention test (given one month after the posttest), and a student attitude test. An instructor's evaluation form was filled out by the three treatment group instructors. The results of the four student tests were analyzed statistically, utilizing the CDC 3600 computer at the Michigan State University Computer Center. The Finn Multivariate Analysis of Variance program was employed in the analysis. Three hypotheses were formulated in the experimental testing of the model, two in the cognitive domain and a third in the affective domain. It was expected that members of the treatment groups would achieve higher mean scores on the posttest and retention test than would members of the compar- ison groups. It was also expected that members of the treat- ment groups would have a more positive attitude toward the experimental method (the suggested model) than the comparison group students would have toward the conventional method of experimentation. The main findings of the statistical analysis were summarized: I I . . . . - ~ O O ‘- .‘v ”Av—Iv- ”yo . - a-fl ‘aoi | I an 1,“ .v. a» “‘5 v. i» ll .5 my; C E 3. .... .L i I n... .J X .l S . I w... .. O. a . 7‘ c l e ... an _... S . . C v v. 3 C . 5 C E . .v .3 S 2. C. 5 .11. .: C . . nu. . S r L. a... u. ... v. E a». r. .1 .a r v w... x s : a .. .. a v ~... . b. .2 .... -s t. .“m. .2... MW max. Shlomo Waks 1. NO significant difference (p<0.9544) was found in the mean scores of the pretest when comparing the treatment and comparison groups, indicating equivalence of groups at the beginning of the lab experiment. 2. Significant difference in the posttest (p<0.0004) and retention test (p<0.000l) between the treatment and comparison groups indicated that the members of the treatment groups learned and retained more than students in the com- parison groups. 3. No significant difference was found in the mean scores within the treatment groups (p<0.8151) and within the comparison groups (p<0.7023) in any of the three tests (pretest, posttest, and retention test). 4. Members of the treatment groups held a significantly (p<0.0120) more positive attitude toward experimentation by means of the model than members of the control groups held toward experimentation through the conventional method. In the Instructor's Evaluation Form, the treatment groups' instructors reported a favorable reaction regarding the application of the model in the electronics laboratory. . u \ .0 V.‘ nu “.4. .1 av yawn t a e p . D Ill' THE DEVELOPMENT AND TESTING OF AN INSTRUCTIONAL MODEL FOR LABORATORY EXPERIMENTS ON ELECTRONIC CIRCUITS IN COLLEGE-LEVEL ENGINEERING BY Shlomo Waks A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Secondary Education and Curriculum 1973 © Copyright by SHLOMO WAKS 1973 DEDICATION To Ayala: For her patience, understanding, and cooperation. ii 1 I..- “"R‘ ”.5 -va - | ::n_‘ “ .‘MVO.-..‘ ‘u,' “A ‘t‘k‘ ..‘ - ACKNOWLEDGMENTS The writer wishes to acknowledge: The assistance and friendship freely given by his doctoral committee: Dr. Stephen L. Yelon, Chairman Dr. Julian R. Brandou Dr. David P. Fisher Dr. James L. Page The cooperation of the Science and Mathematics Teaching Center and the Department of Electrical Engineer— ing and System Science at Michigan State University. iii A" ‘ u .10... V. .'~" A" ‘ it ~.'. 5. .--" ‘sv‘ ‘ u- h... V. 7 ‘0 7’? “. .,\‘ \ ‘ *I .— O..J 0'1, 0 4 O) i "t I Y\" ‘s‘ m .I l (D (.1 "I {'7 TABLE OF CONTENTS Page LIST OF TABLES O O O O O O O O O O O O O O O 0 O Q 0 Vi LIST OF FIGURES. . . . . . . . . . . . . . . . . . . Vii LIST OF APPENDICES O O O O O O O O O O O O O O O O O Viii Chapter I 0 INTRODUCTION 0 O O O O O O O O O O I O O O O 1 Statement of the Problem . . . . . . . . . 1 Importance of the Study. . . . . . . . . . 3 Definitions. . . . . . . . . . . . . . . . 5 Purpose of the Study . . . . . . . . . . . 6 The Behavioral Objectives. . . . . . . . . 6 The Model for Electronic Circuit Experiments_—In Brief 0 o o o o o o o o o 8 DevelOpmental Sequence of the Model. . . . 14 The Hypotheses . . . . . . . . . . . . . . l9 Assumptions. . . . . . . . . . . . . . . . 20 Limitations 0 O O O O O O O O O O C O O C O 20 overView O O O O 0 O O O O O O O O O O O O 22 II 0 BACKGROUND 0 O O O O I O O O O O O O O C O O 23 Introduction . . . . . . . . . . . . . . . 23 Background of the Prob em—-The Sprea of Electricity and Electronics. . . . . . . 24 Electronic Circuits Laboratory Experiments--Past and Present. . . . . . 27 Review of Literature on Learning Principles and Instruction Methods . . . 36 Summary. . . . . . . . . . . . . . . . . . 56 III. DEVELOPMENT OF THE MODEL AND PREPARATION OF EXPERIMENTAL MATERIALS. . . . . . . . . . 59 Introduction . . . . . . . . . . . . . . . 59 Description of the Model Components, Their Rationales and Sequence. . . . . . 60 The Development of Media Materials for the Experimental Study . . . . . . . . . 80 smary O O I O O O O O O O O O O O O O O O 82 iv Page IV. THE EXPERIMENTAL TESTING OF THE MODEL. . . . . 85 Introduction . . . . . . . . . . . . . . . . 85 The Sample . . . . . . . . . . . . . . . . . 85 The Population . . . . . . . . . . . . . . 87 The Statistical Design of the Experimental Testing . . . . . . . . . . . 89 The Testable Hypotheses. . . . . . . . . . . 94 Running the Model in Practice. . . . . . . . 96 Summary. . . . . . . . . . . . . . . . . . . 99 V. ANALYSIS OF RESULTS OF THE EXPERIMENTAL TEST . 102 Introduction . . . . . . . . . . . . . . . . 102 Statistical Analysis of Cognitive Domain Measures. . . . . . . . . . . . . . 103 Statistical Analysis of Affective Domain Measures. . . . . . . . . . . . . . 109 The Instructors' Evaluation of the Model . . 116 Summary. . . . . . . . . . . . . . . . . . . 117 VI. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS. . . 119 DiscuSSion O O O O O O O O O O O I C O O O O 119 sumary. O O O O O O O O O O O O O I O O O O 122 Conclusions. . . . . . . . . . . . . . . . 126 Recommendations for Further Research . . . . 127 BIBLIOGRAPHY O O O O O O O O O O I O O O O O O O O O I 130 APPENDICES O O O O O O O I O O I O O O O O O O O O O O 135 10. 11. LIST OF TABLES Sections Assigned to Instructors. . . . . Weekly Schedule of Laboratory Sections. . Means for Pretest, Posttest, and Retention TGSt. Q o o o 0 O o o o O O 0 ANOVA Treatment vs. Comparison Results. . Statistics for Regression Analysis With One Covariate. . . . . . . . . . . ANCOVA of the Cognitive Domain Measures . Analysis of Variance--Within Treatment Groups Multivariate Analysis of Covariance Results Distribution of Student Attitude Answers and Univariate ANOVA Results (Treatment vs. Comparison Groups). . . . . . . . . Multivariate Attitude ANOVA . . . . . . . Statistical Decisions . . . . . . . . . . vi Page 89 90 103 104 106 106 108 109 111 114 118 . l x . C V. .r \ .~ .2 . 1 .c 3 C L. S I C a. . . v. I ”I... a» .1 "nu H: “L A: by TL "w P» a. .. . nu a“ \ku mu uh .1 vi e V. | 0 O 0 0 ”N; u . alt 3 I... .\d .u o It. LIST OF FIGURES Figure Page 1. A Model for Electronic Circuits Experiments . . 10 2. Developmental Sequence of the Model for Electronic Circuits Experiments . . . . . . . 15 3. Hierarchy of Knowledge. . . . . . . . . . . . . 43 4. Introduction and “Stable-State Operation" Experimenting Procedure . . . . . . . . . . . 68 5. Investigating External Effects on the Circuit's Operation . . . . . . . . . . . . . 76 vii \ a 1 "" ‘Ifl V - .- -~--~.uu- I. r. Inc.“ ’4 L. on... ‘ K“- V rur~ .‘. A H VP!“ .3, .1 HI I \‘4‘ u‘. .‘c‘: \l—. ,. fies-:1: CIR: f?! 7 F. Ilrh.. .“g‘ LIST OF APPENDICES .Appendix A. THEORY SHEETS. . . . . . . . . . . . . . B. EXPERIMENT PROCEDURE . . . . . . . . . . C. THE SCHMITT TRIGGER-~ANALYSIS AND APPLICATIONS . . . . . . . . . . . . . . D1. PRETEST. . . . . . . . . . . . . . . . . D2. POSTTEST . . . . . . . . . . . . . . . . D3. ATTITUDE TEST. . . . . . . . . . . . . . D4. INSTRUCTORS' EVALUATION FORM . . . . . . E. MEASURED RESULTS OF THE SCHMITT CIRCUIT OPERATION. . . . . . . . . . . . F. IMPLEMENTING THE MODEL IN THE LABORATORY viii Page 136 172 189 201 205 209 211 213 220 CHAPTER I INTRODUCTION Statement of the Problem The main objective of this thesis is to develop an instructional model for laboratory experiments on electronic circuits and to test this model in the College of Electical Engineering at Michigan State University. Successful experimentation with electronic circuits rmeans bringing constructed circuits into operation according tx: predetermined expectations. In some cases, the experi- rmentation also includes constructing the circuit under (Experiment. Furthermore, at the college level, students have to acquire the ability to introduce necessary modifica- tions into the circuit in order to fit it into a given new system with specific requirements. This kind of training is a key factor in becoming a good electronic technician or engineer. Some of the problems in traditional laboratories are: l. Forcing all the students in a group to proceed at the same rate is boring to the fast students and leads to failure for the slow ones. Goldon H. Flammer, from Stanford University, asked among other questions: AO' ..v‘~ C. D. * . n O c o b. +- 6132} ‘ N :0- i- ‘F 6-3. bote :5 v. {LA ‘t. How can we individualise instruction, that is, allow the student to move at his own speed? Why should a brilliant student be forced to make four years of his B.S. and the handicapped (in most cases due to accumu- lated ignorance) student be forced to meet a quarter deadline or flunk out? Individualized or self—paced instruction appears to have the answer to most of the questions posed above in a way which is acceptable to students and teachers alike.1 2. Instead of dealing with meaningful difficulties arising during the accomplishment of the experiment, an instructor spends most of the time reiterating technical instructions. 3. The student's lack of physical and mental involvement 1J1 the process of experimentation in the electronics lab lcnders the chances that he will learn the amount of knowledge he should. At the Third Annual Audio—Tutorial System Confer- ence, which took place at Purdue University in November, l972, a team from the Engineering and Technology Department at Western Michigan University worte in their conference paper: Engineering curricula is continually under pres- sure to increase the amount of knowledge transferred to the student without decreasing the quality of edu- cation. One of the best ways to increase this Gordon H. Flammer, "A Behavioral Analysis Design Of an Engineering Course Using Individualized Instruction," Stanford University, n.d., p. 2- . 31335181 I . . II... n f.-. *u.\v.o UC- a ~ . a. n 82. v.‘-u“n no r. ." “0“: *CQA‘OI I ‘ U “V"‘ A" an» :.U~-conl ‘OVV‘ \':--.' .AC v.3 .~.': V- Lth I c. a: " A .._. b-u‘-..b “J .V “,.o ‘ ‘ Q r‘ b: 5..» S"Ver v~:-, n.v‘:‘ PI. ‘ w nah :a "‘- ¢ 5"‘Dbar' 4| .‘R‘ q n ”F‘A' ivhg‘..v‘ccxv ' -‘ I L :Xu‘ ~ f‘y- ._ :¢V¢a.;CI\ ‘I ~A‘ u:.._s 'wyfi ‘V I: “at“ A: 5“ . e‘ectvfiv‘.’ -k..‘ C; . V “e-§C. transfer of knowledge is through student involvement which demands initiative reactions from the student.1 4. A student's over-dependence on an instructor's help vfliile working on the experiment in the laboratory is another jproblem encountered in the traditional group laboratory. Many of the circuit malfunctions that usually require a student to wait for an instructor's help can be corrected by the student himself if appropriate guidance is provided. Importance of the Study Modern industry, computers, automation, communication bur telstar, transportation, radio, television, instructional 'Uechnology, modern medical treatment and research, space eaxploration, national security, and other modern accomplish— rments would be impossible without a highly developed science <3f electronics. More and more people are needed in this field. In the Technical Education Program Series, a predic- tion of further dissemination of this field is stated: "Meanwhile, science promises that future develOpment using applied electronics will be even more dramatic than the developments witnessed during the past three decades."2 Thus, " Jerry H. Hamelink, James Kauppi, and Gary Roberts, Tbe Multi-Media Approach to Learning at Western Michigan University"(paper presented at the Third Annual Audio- Tut9rial System Conference, Purdue University, Lafayette: Indiana, November l-2, l97l). 2U.S. Department of Health, Education, and Welfare, Office of Education, Electric Technology: A Suggested Z-Year EQEEJEigh School Curriculum, TechnicaI Education Program Series No. 2A (Washington, D.C.: U.S. Government Printing Office, 1969). A a..- db I‘.' u .p.‘ 4% cvr~ obv- “. [Ila-Ra‘s nn~w ~:'V"'U V VOA-:1 5 .- "5- Coun- ‘ an: n;...’ toaud- . :1 . ‘ ‘..b-‘\‘e s: s-‘ . . ~a~a.“ ‘ n ""¢¢-...‘— ‘ - ~ . "a- 3 .- u~ Qf" .-‘~.g ma ~-':. I" m. “-a. .1 . ‘. ‘Y‘A. V“» A ““3381 t; «5 stulouts m.‘ . W C; ‘ «‘e‘d. "5! AC. 5 *5 ‘tsll+s C: I « r ‘ seacr‘ihfi .d 3 gr it might be helpful to develop appropriate instructional tools in order to enable increasing numbers of students to become competent electronic engineers or technicians. The subject matter in electronics is abstract in nature. A man's senses are not constructed to feel (without harm) any electrical quantities like voltage or current. He can only observe the result of electrical activity~~light, sound, or movement. This abstract character of the subject limits a student's ability to master electronics. A desirable method of learning electronics should include software based on both an understanding of the teaching—learning process and a knowledge of electronics as subject matter. Hardware should include varied forms of media. The resulting ease in experimenting with electronic circuits may help to increase the concreteness and useful- ness of many applications of electronic circuitry. The audio-tutorial method of instruction, which has the feature of combining practice with theory, may be the channel through which electronics will reach those potential students who would not otherwise become acquainted with this field. The audio—tutorial approach to college—level elec- tronics has been implemented at Texas A&M University. The results are strongly in favor of the audio-tutorial method of teaching electronics. James L. Boone, Jr. and William F. Smith wrote in their paper: I ‘ V. —\ prx G . O . n . .0» . .u PC a» " KM» «‘ VL Nu. «G i: :8 w. .r. :u v. r. .. . .. . . . . a 3 t 1.3 3 an . t C a S C t .u u. S .3 a r J. r i S... C .u I E C I n- e S I .l a C _ u C C C h. E F E .. e i. a. .u .2 e C a Tn 3 ¢. I t n,“ C Ti .1 .6 .1 +. a.» :. 4m. M . a .C.. 2.3 S S n I 1 C e e... is an S g. e I CL 5 a a“ u‘ .5 J. a 5 S o e s. a. .3 C I 3 Lt v. v. r. ... E t .C .. E T. .. :. . . a .3 e .. ”a .. . r e C. a e . 3 .h 3.. . 5 L“ o C e T" . . Tn a r C a. .3 C. e .5 o. «v A.» #4.. nu ‘5 fi.‘ .3 .u.. G» ... nu L. u u a w . . .s . a: a. C s ad S. ax. _.~ a» uh fl». AV n R... v. After one year of Operation it has been found that the electronics students have achieved higher grades and have progressed through the course mate- rial faster than during the previous year when con- ventional methods were used. Furthermore, each student has become skilled in the use of electronic measuring instruments. This has not always been accom- plished in previous semesters, as the weaker students lean on the stronger students. The audio—tutorial system eliminates lab partners—~each student is on his own. We are convinced that the audio-tutorial system of instruction is an excellent approach to teaching electronics. Time is needed to develop more visual materials and software to supplement the system. The task at hand is to develop these materials, . . . We encourage other electronic instructors to try the audio-tutorial system of instruction. In high school level electronics, audio-tutorial instruction turned out to be successful at Jonesboro High School, Jonesboro, Arkansas, where a course of "Basic Electronics" has been taught since 1969.2 Almost 90 per cent of the students chose to continue learning about electronics using the audio-tutorial technique, while only about 10 per cent preferred to proceed through the conventional method of learning electronics. Definitions Terms used in the study with which the reader may not be familiar are defined below: 1James L. Boone, Jr. and William F. Smith, "Audio— Tutorial Electronics Instruction" (College Station, Texas: Texas A&M University, n.d.). (Mimeographed.) 2John S. Morgan, "High School Basic Electronics (Modified Audio-Tutorial Style)." (Mimeographed.) Electric (Electronic) Circuit-~The entire course traversed by an electric current. Oscilloscope-~An electronic instrument for projecting the graphic presentation of the voltage at a measured point as a function of time (or other voltage). Waveshape--The graphic presentation of voltage at a certain point in an electrical circuit as a function of time. Instructional Model--An isomorphic representation of certain aspects of a larger and more complicated instruc— tional system. Purpose of the Study The purpose of this study is to improve a student's understanding of the operation and application of electronic circuits, and to increase his laboratory skills through the use of a systematic approach involving audio-tutorial tech- niques. A model for laboratory experiments on electronic circuits is suggested for implementing this systematic approach. The Behavioral Objectives Objectives in a curriculum design describe the student's behavior at the end of a course or another learn- ing unit. The learner's behavior is characterized by his demonstrated visible or audible action according to speci— fied conditions and standards for adequacy of performance. In a technical field of education like electronics, introducing behavioral objectives into the curriculum might . , . " ‘ fir- n . .AS $3 5.5- an. .‘zgnv.u;“_ 0”: A.a~ b- JV » - ° f' . ““ L o ,. u...(-e'_ C- ~ Y“ A be. \I, O‘— ‘ u A —~'. .Qtlu a s .. ‘9.~- A V » hora-..‘_ ““‘.‘— U.§V\l.\. a..‘t‘ :l‘n’BS are i. F ‘5. «a c 5":5 Lor a.. “\. ‘ . ' ‘ a A“ ‘ fib‘i:\‘ ‘3 LT.‘ ‘ “ I - 7 t‘ 'y—_. ‘ LO 3.).r‘: IN“ ”I ' q VQ§V ‘l :5 ‘ \- ~-.' ‘4. 54“. 2' pfi‘.hs. b‘“‘ it t.“ -‘e X’av“ ‘ 3. prer‘i :‘r fiVA‘ as A: . '\ 1“ ch‘ ~ 5 COL‘QH,‘ U‘. A V Y A 41~ “'B ‘» be as helpful to the teacher as it is to the student, in clarifying an instructional destination. More and more technical institutions are beginning to use behavioral objectives. One of the most active insti- tutes in this field is the nonprofit educational corporation, The Instructional Objectives Exchange,l which prepared a booklet of behavioral objectives in electronics. In Chapter III of the present study, the reader will find a sample of the behavioral objectives specific to the circuit under eXperiment (Schmitt Trigger). These objec- tives are in accordance with the general behavioral objec— tives for any electronic circuit under experiment, and are stated in the following order. Given a diagram of the electronic circuit under experiment, the student will be able to do the following: l. Explain (orally or in writing) the operation of the circuit and the roles of the various components of the cir— cuit. 2. Point out the expected waveshapes of the voltages at the various points in the circuit. 3. Predict the possible changes in the circuit opera- tion as a result of a great change (over 70 per cent) of one of its component values or feeding sources. Examples of acceptable answers: The circuit will not operate; the transistor will be in saturation (or in cut off). lThe Instructional Objectives Exchange, P.O. Box 24095, Los Angeles, California, 90024. A. '2‘ .. u‘h-ov-I . “ n ‘ .133 JO Q‘s—5‘- . .. ' .. - _' . 2' ;V~v~r~.‘ ‘.-.y.v..'v ~ Q-..‘ .. v~.a.,. ’ ~' I 7" C u . A..- ‘ - A...“VH'~‘ H h— “ ‘II‘V‘vsav‘ .‘. A‘Vfl‘\. ._ "N "~vu- b. H I F;Vv. ‘ . v: .9- .2. AV "V‘\~..“~ ~ it. M‘ “‘.H ‘ “‘vfl V I 4 vu‘: 7“?“ ._‘ I a"- a.~ 8. u H ‘~\, l L“_) at], S..‘. s, a"~.. . "‘"H 13"0 4. V i . .‘ . Q A I “V " ”Jew: V5 ‘ . ‘ ‘H‘ me. ~, v‘:n-.; V‘kt E‘I“ I ‘- 5. 5”: g 0‘11}! 4. Perform a series of measurements according to given tables. 5. Realize how theory "works" by comparing the measured results with the calculated ones. The maximum acceptable difference between measured and calculated values is 30 per cent. 6. The student will point out possible reasons for the differences between the calculated and measured results. 7. The student will name at least two applications of the circuit. 8. Given a new situation (different supply voltages or driving level, environmental changes like rising tempera— ture, additional loading, or increasing frequency of opera- tion), the student will point out the necessary modifications which have to be introduced in order for the circuit to oper— ate correctly under the new circumstances.1 The Model for Electronic Circuit Experiments--in Brief A detailed description of the model for electronic circuit experiments and the phiIOSOphy behind it is given in Chapter III. Only a brief presentation is given below. The development of this model is based on the following factors: l. Theory of learning. 2. Teaching and curriculum development experience in 1Only for college and community college students. .‘ a n a A s .u III-II!!! . o. .3“ _... unl .r. ._ ..- : 3 s. .2“ w... 5 a. r a. n“ C . E u“ A . . 3 .u a» A "PM \n .3.“ A» I“ u n v .ai ‘fi‘ ‘. can fly ,a. ”C . «: . S.» n» .Mv h. 2H C u. r. . C. . a . . r t . . In v; w. M‘. i. .u .u «(J .ru n. «a. .: . ~u. . . 2. .D ... ab av C» L. A: “n a: s . . . ‘3 ..u L. c .. a: :. .u a A: . . .n . . 2- : . :n .2 as ~._ c~ «(J electronics at the high school and community college levels. 3. Knowledge in the electrical engineering field. A condensed presentation of the model is given in the block diagram in Figure l. The sequence and roles of the various blocks are described as follows: 1. Prepare Preliminary Work At least a week before the laboratory experiment, a student is informed about the topic of the experiment. He is supposed to come to the laboratory after completing the assigned reading and calculating some of the circuit compon- ents and expected outcomes of the lab measurements. These calculations will be used as comparison references of the measured outcomes of the experiment. Some instructors may require a student to hand in preliminary work before start— ing the experiment. £32222 The student "enters" the lab with an incomplete practical circuit, a lab manual, a set of varied media, and electronic equipment and materials. 3. Listen and Watch, Audio-Tutorial In this stage, a student gets to know the circuit under experiment. Its operation and applications have to be demonstrated through multi—media means like a tape—slide presentation, or a closed loop film. An effort has to be Inade to arouse a student's curiosity and interest in the circuit, by posing a problem which might be solved by this u /./p I . lllw all". w.......~ ~.,.s~—.~.:. .~<:_w....:... ....< ._l._,..<.:z. _...._.~;,...\l 77. ...C.: H~x~lu..(\.:}. .- . «ill - - L--- I‘lllxll] ~ 10 2.2 O 3...: 262m .muquwuomxw muwnouflo cacouuomau new Hmcoa «II.H muaofih 0H umwuumom mxma m Emanoum :mflmwo w :ofiumoflamm< w>ummno mafieluxocwskum unmEcouH>cm a mucwcomEoo mommuao> mou50m .mamflumume ppm ucmEmwsvo oficouuowam cam mflnwsfiuase .uflsuuwo Huofluumum mumamEOUGH cm nufizx m If 3:35-033. :uumz m cmumflq h umcfimcmao coca coflumuomo :0 powwmm w>ummno . m m uflmmwm o: d uoorm cannons o v mmzam> pmuowmxm mm» 05am> 03Hm> omuommxm on mummeoo wuommxm ou mummfioo uwzwuwmomzu a wudmmwz uoo g whammwz u H o onammmmo q¢szoz .U.¢ mmomf a student, but also increases his satisfaction and self- czonfidence, while it frees an instructor to deal with mean- ingful difficulties arising during the accomplishment of the experiment. 8‘- .,.A A. van Q .. Inn: v..\-¢-- .. H... ‘F‘ .1. up.“ ,. 'i"‘vvot huh. arr..p,‘. “d vvnA'.,.‘.“d . - "C" .yA—n ._ ""'" ‘ov... . ‘Nsu. 4 fl : ‘v-du.‘\ ..‘ n .D'p A.— J-QV.‘4 r_-‘. I U 5 ~83:”v.: a ..-_.~“ a . MA“. ‘ vu‘uu ‘ ‘e‘. A .c: . =‘fi ‘;“ - u...‘ ‘ ‘H-\‘. s . .:S§ ‘. ’ho :‘A".'~ “V": A 1 N": ‘ w“ n "v- F. “V “v“ , O “K “it, . vyyy ‘. ‘ A .V “HQ 5“» ‘3‘"... by. ‘ ‘ g I ‘ H A.‘ A: . \- G C “u “~_h ‘0 n4\ ‘w ~- .6. ‘. .“,i I C I am ‘V ‘. ~ :‘1... L‘ "‘ 5"” ““9 v- k . N; ““‘S S‘~ H’I ~‘uc: -\ 12 It must be emphasized here that merely operating the circuit successfully and getting reasonable comparisons between the calculated and measured values is a process of continuing evaluation. The student gets continuous evalua- tion from the Operational behavior of the circuit; this is actually natural evaluative feedback, which may result in strong reinforcement. 6. Measure A.C. Nominal Operation After establishing and measuring the D.C. conditions of the circuit, the dynamic (A.C.) nominal operation is per- formed, measured, and compared with some expected values. At this point, some instructors, especially at the high school level, may introduce some application presentations and finish up with the final evaluation step, i.e. a post— test. However, for a college and community college student, the model Offers some additional steps in the experimenta— tion procedure, namely further analysis and synthesis options of the experiment. 7. Observe Effect on Operation In this stage, a student investigates the effect of changes in source voltages, component values, and environ— mental conditions on the Operation of the circuit. Frequency and time reSponse of the circuit are also investigated in this stage. 8. Observe Application In the application step, several block diagrams, illustrating actual applications of the circuit, are v as. 'A ‘0‘ .3 a: ~\~ .w.¢ flue-H ssh-V mm: ‘ivtu 13 presented to a student. It is recommended that varied forms of media be used at this point—~a short film, or a closed loop film, or a slide presentation from the "prac— tical, real world" might be helpful. It is recommended that a learner be exposed to an actual practical electronic sys- tem that includes the experimented circuit. 9. Design Problem The design stage is primarily a college—level stage. It is actually a part of the evaluation. Here a student is asked to suggest appropriate modifications to be intro— duced into the experimented circuit to make it compatible with a given system having new conditions Of loading, feed— ing voltages, environmental restrictions, etc. 10. Take Posttest Right after finishing an experiment procedure, a stu- dent has to submit a written report, including his precal— culations and measurement results of the experiment. A post— test might be given in written, oral, or performance form, or even in some combination of the three forms. The main points of the model might be summarized as follows: 1. Use of audio—tutorial techniques. 2. Utilizing the oscilloscope as a powerful medium in studying electronic circuits; for instance, scanning the out- put characteristics Of a transistor, or scanning the wave- shapes at various points in the circuit or scanning the actual transfer characteristic of the circuit, that is, a ‘ .. .c .. a ‘I‘|l‘l“ . .u a... w» w“ . A: -k v. . Av J :u w. .1 .2 r~ . 5t . C 2. ... C. . . . u. o v m. . a. T. .2 r». . a ago A» . us. . .3 . o C an“ n .C In. :2 :J .. av «4.. a. .. a “A . Mum w” a. i. .» .-u r: ..u .. . i. K“ .C m“. ._.. a 5 T. ~ .. a» a. C St 3.. . “u I .. . 2» a.» s B u. a: .(. C. 5 a» .p» :w 1‘ .‘h V§ .Fh ~—n Ru 4 x 14 the output voltage (v0) as a function of the input voltage (Vi)’ 3. Use of guides like flow charts for the experiment procedure (optional). 4. Having a student discover by calculating the values he is going to measure. 5. Some features of "programmed experimentation." It is a combined series of mental and motor activities per- formed by a learner. A student is exposed to an ordered sequence of stimulus items to which he responds. His reSponses are immediately reinforced by the natural feed- back he gets through measuring the circuit operation. 6. The modular structure Of the model enables its use at different levels, i.e. engineering, community college, technical schools. It is important to maintain weekly sessions of the instruction team and the whole group of students performing the electronic circuits experiments. These sessions are to be dedicated to discussing the preceding and forthcoming experiment, to surveying special problems, to exchanging recent learning experiences among the students, to stating conclusions, and to administering oral exams. Developmental Sequence of the Model An overview of the develOpmental sequence of the model is shown in Figure 2 in a block diagram format. .mucmEaummxm muflsouflo oscouuomam How Hmpofi may «0 mocmnvmm amucmfimon>monu.m musmflm nonmmmmm Hocgusm now mcoflumpcmfifioomm 15 : muasmom may mo mammamcd HOOHpmHumpm I ampoz mcu mamflumumz mamflumumz mEmuH coapmsHm>m Hmpoz may no mo mcflumms mo unomna I. aflomz mo coaumwuomoo xmme mamcoflumm Hmucofifluomxm mumcafiflamum ucmEmoam>mo ; mm>wuomflno . - pcmEmon>oo rl'l mGOHOMOHMHOoz Ill-1.1. 16 The rationale includes the reasoning behind the model, its importance and purpose. The second stage includes the development of terminal objectives, task descriptions, and tests. The behavior described is that which the student is to perform when com— pleting the experiment on a given electronic circuit. A task description inCludes detailed guidance for the student dur- ing the experiment procedure. The evaluation used in this study includes four tests: pretest, posttest, retention test, and attitude test. These four are not necessarily the only evaluation tools for an instructor using this model. These four tests were used by the researcher to evaluate a partial representation of the model. Other instructors who use the model may use dif— ferent evaluation methods, like student reporting or oral testing. The development of media materials includes creation and selection of both hardware and software. A great deal of time and money can be saved by selecting from existing materials rather than by making them. In order to try out the model, the researcher was given permission to apply its requirements to the "Electronic Devices Laboratory" course, E.E. 484 (senior level) in the College of Electrical Engineering at Michigan State Univer- sity during the first two weeks of fall term, 1972 (three hours weekly). The tOpic of the scheduled experiment was: "The Schmitt Trigger--Theory and Application." For this . oer-A I“ .v~.v, L..- . '\ .3... ”no. wen- . bUU- I - CA». “flu". . q :5... v“ s A“ 17 tOpic, the researcher wrote the Theory Sheets and Experi- ment Procedure for the students who would use the suggested model.l Two presentation forms were prepared by the writer-- a slide-tape presentation of circuit theory and applications, and an oscilloscope to be used as a diagnostic tool of the Circuit's practical Operation. In the preliminary tryout, the materials were sub— mitted separately to an electrical engineering instructor and a student from the selected population. After getting their remarks, necessary modifications were introduced to improve the media materials. A total of 108 studentSVNMs divided into ten lab sections. Five of the sections (treatment groups) used the suggested model to perform their lab experiment on the "Schmitt Trigger" three hours weekly for two weeks. The other five sections (comparison groups) performed the same experiment under the traditional method of experimentation. The treatment groups had three instructors and the compari- son groups had two other instructors. As has already been mentioned, the model was eval- uated by four tests: pretest, posttest, retention test (given one month after the posttest), and a student attitude survey. The three treatment group instructors filled out an Instructor's Evaluation Form concerning the model (Appen— dix D5). lSee Appendices A and B for a copy of the Theory Sheets and Experiment Procedure. r- baby . a .. U A (I :u: V 2”" .ou-‘o' VJ Mu— In?! way-nay ~1st- . .v . VF'QAOuu—A'.‘ ' F .vvv»-.v..u _‘ n“ p .. o..{ I'~ .0. a n,‘ 04‘, b "v '. 3 -‘*. 18 The results of the four tests were statistically analyzed utilizing the computer at Michigan State University (Finn program). According to the findings of the study, recommendations for further research are stated. The model should never be completely finalized; it must remain Open to further changes and improvements accord- ing to future necessities. Use of the suggested model of experimentation is not restricted to certain electronic circuits. It may be used for a great variety of circuits, like amplifiers, oscil— lators, multivibrators, and other switching dircuits. The circuits may be constructed of discrete components or inte— grated ones like those used when dealing with the more modern portion of electronics. The model does not impose a rigid system of experi— mentation. On the contrary, the instructor and students are encouraged to change or add their own modules, or use those media which will result in optimum results for the learner. The suggested instructional model for experimenting in electronics was prepared for college—level students. However, since this model is constructed of small modules, it may also be used for lower level students, i.e. at the community college or high school level. For instance, high school students do not have to work on the "synthesis" part of the experiment. Design capabilities are required only at the college level. . fl - ...-' V:AI:‘3‘ tea - 1 o ~AQ- p. ,- UC “Ch ‘0 b v . . . 0n» ,.. A _ f‘ bu: my": ‘_ CIA“ ."" : "Vu. Vni- . ’ . 9r: A.C.N“. . .. "“" VVV-A-\.- C ‘ A‘: 1- ? v , ."" ‘T- n 'v~ "' ecu .21" u ch‘Qj t.” ~":~~'\— a... ‘ . n. twagr “AV ul.m.... 1 VV‘ V.“ L... .d 5.‘e Chin” .“h - ‘ “I“ ‘eSt, I . "Q‘V 5“ 7‘“ ' MCCAEEn tfic‘ ‘s c . C, t 19 The Hypotheses The hypotheses for the tryout of the model are of a general nature. At this stage of development the purpose is to get an overall idea of the characteristics and effects of the model in comparison with a conventional method of instruc- tion. Consequently, three hypotheses were formulated, two in the cognitive domain and a third in the affective domain. The hypotheses are given in testable form in Chap— ter IV, and are stated only briefly below. First, it is expected that members of the treatment groups will achieve higher scores on the posttest (Appendix D2) than students in the comparison groups. It is also expected that there will be a significant difference in achievement test scores between the treatment and the comparison groups one month after the students have completed their experiment (Reten— tion Test, Appendix D3). Finally, it is expected that there will be a significant difference in positive attitude toward the methods of experimentation with electronic circuits, between the members of the treatment groups and the members of the comparison groups. For instance, a smaller percentage of the treatment group members will prefer to use the con— ventional method of experimentation in the future than the percentage of the comparison group members preferring the conventional method. In Chapter VI, specific hypotheses are made available for the ongoing experimental research of the model, concerning CI“ J~:v¢o.v J... O .iwun-y hr va- non-oto'jl F‘rl“ L0 ...v —‘ I ‘ ’ :5‘V‘ R: . u.v~..-\'“ . h—LV‘ .- ~ 10“. ...v . r ‘- FY~ nay. 50 ~-: . 3 u. ,. o ‘..L ‘V—q ‘ “:3 ”£“5 : h”~“b u A...“ .“t ‘Vu C“ :1. . C‘ -. ‘L‘fl‘ ~ ““‘tu “h J ‘.\a -.' .. . §.. ‘“ L n.4,)... “(‘3 ~.‘ VT; ‘4 Q \ M t" “Mn 4.“ ‘- L ‘fi 3. (». hrs 3“ Hi SV‘ . dflja . A“ 4x.» u ‘L‘. Lu‘e 20 specific independent variables of interest like efficiency, timing, or use of different multi-media setups. Assumptions l. The sample of 108 students from the Department of Electrical Engineering at Michigan State University did not differ from similar populations in other colleges of engi- neering. 2. It was assumed that no student had had an opportu- nity to practice the questions included on any examination. 3. There was no interaction between students of the treatment and comparison groups, nor between instructors of the comparison and treatment groups. Since the comparison groups had different instructors than the treatment groups, there was no carry—over of the model's methods of experimen— tation to the groups. 4. There was no teacher effect. (This can be shown by finding no significant differences when comparing the scores within the treatment groups and within the comparison groups). Limitations The study was limited by the number of students (108) in the course E.E. 484-—Electronic Devices Laboratory I at Michigan State University. The statistical analysis of the results of the three tests (pretest, posttest, and retention test) involved only 80 subjects because only those students who took all the three tests were included in this statistical analysis. 21 Equipment, manpower, and space limitations made it impossible for the student to perform the experiment at his own convenience. Each of the ten lab sections had its fixed three weekly laboratory hours of experimenting in the elec- tronic lab. Limited quantities of electronic equipment prevented the testing of the model in completely individualized format, so in this experimental test of the model the students worked in pairs. The time elapsing between the posttest and retention test (retention period) chosen was only one month because the researcher suspected that during this period some of the students might pick up additional information concerning the Schmitt Trigger in other electrical engineering courses. According to the Cornfeld-Tukey argument, the pOpula- tion of this study might be considered those students in courses similar to the ones taken by electrical engineering seniors at Michigan State University. In order to expand the pOpulation, further field studies should be carried out to investigate the external validity of the model, as sug- gested in detail in Chapter VI. Conclusions concerning external validity-~i.e. application of the study to other student populations-—should account for the limitations mentioned. aruzfl .6. . ”A A.A~.'A‘§“ : to:v~.&vna-v fil'y‘ V‘ cm “TL -.. r- 5:35. A t- . C ‘ 2" ‘hh ..,.‘ ‘ . ‘.=V - .LG 5:.” . e on» mu“- ' 5 ’ “at . .' "_ ' V. . ‘ “““‘Abu ,. ; . '25": Tnfi‘ .“. “‘\v-u “ Rn . f‘ .‘n c , VE‘ICVtt‘ ‘r. sJA C b Ym ..n .c‘“. K ". a ‘ «:C‘ A I ‘ H VA. Q ‘~‘ ' 5:4» res‘i‘ .‘ 22 Overview In Chapter II, the background of the problem of electronics instruction is given. The traditional method of experimentation in electronics is reviewed. Chapter III contains a detailed description of the model, including an example to be used in the experimental test. A report of the development of media materials is also included in this chapter. The experimental test of the model, description of the sample, statistical design of the study, and the process of "running" the model are described in Chapter IV. Chapter V consists of the analysis of the collected data. Included are results and interpretation of the data collected from the attitude survey and instructor's evalua— tion form. Discussed in Chapter VI are the conclusions based on the results of the analysis and recommendations for fur— ther research. CHAPTER II BACKGROUND Introduction Curriculum modification is a continuing process, especially in such a dynamic field as electronics. During the short history of this field, many changes in content have occurred, mainly since World War II. It seems that methods of electronics instruction are far behind the needs of those who would like to be acquainted with this field. The search for better means of instruction has been and should continue to be one aim of education in general. The changes in physics content and the amount of research in instruction of physics at various levels serve as examples of this continuous process. The value of reviewing past work (even in less dynamic fields than electronics) to improve instruc- tion was pointed out by Dewey: "The way out of scholastic systems that make the past an end in itself is to make acquain- l tance with the past a means of understanding the present." Therefore, we must not be content with the status quo. We 1John Dewey, quoted in Sidney Hook, Education for Modern Man—-A New Perspective (New enlarged edition; New York: Alfred A. Knopf Publishing Co., 1966), p. i. 23 24 must examine the past accomplishments as well as future needs for methods of improving the teaching of electronics. A brief review of the ever-growing field of electri- cal engineering and a description of traditional and non- traditional ways of experimenting in an electronics lab will aid in understanding the reasons for developing the suggested model. In this chapter the reader will also find a short literature review in three areas that are closely connected with this study: audio-tutorial instruction, individualized instruction, and mastery learning. Background of the Problem-~The Spread of Electricity and Electronics Electrical engineering is less than 100 years old, but magnetism and electricity have been known and observed for thousands of years. Chinese emperors about 2000 B.C. used a lodestone for pointing always to the South. Later, the Greeks knew about amber ("elektron" in Greece) attracting light objects after being rubbed in a certain way. Dunsheath wrote about the first compass: King Solomon, Son of David, is said to have employed the compass and indeed to have invented it, while certain verses in Homer's Oddyssey are inter- preted as evidence that the properties of the lodestone were understood and applied in his time. Dunsheath also wrote about the first description of magnetic induction in iron: lPercy Dunsheath, A History of Electrical Engineering (London: Faber and Faber, l962), p. 22. 25 Lucretius (55 B.C.) for example, considered that the lodestone had hoods on its surface which engaged with rings on the surface of the attracted iron. This same poet, in his "De Rerun Natura" vividly des- cribes magnetic induction in iron by the lodestone in the following lines: When without aid of hinges, links or springs A pendant chain we hold of steely rings Dropt from the stone; the stone the binding source Ring cleaves to ring, and owns magnetic force; Those held superior, those below maintain Circle neath circle downward draws in vain. Not until the nineteenth century did the discovery of the close relationship between electricity and magnetism bring about the foundation of electrical engineering. The great push for the expansion of electrical engineering came with World War II. The electrical engineer- ing departments began to turn away from teaching power elec- tricity emphasizing machinery and tramsmission, and moved beyond offering only a few elective courses in electronics and communication. Van Valeknburg wrote about this change: The technical developments of World War II emerged as fruits of the labors of engineers and scientists from a variety of backgrounds: antennas and propaga— tion, microwaves and microwave electronics, servo— mechanisms (later called controlled systems), pulse techniques, radar, network synthesis, communications and accoustics (especially underwater sound). To accommodate all of these new subjects, it was obvious that an upgrading of the curriculum was urgently required. This was accomplished by the adOption of the option system. The older work in power was retained as power Option. The newer fields were included in electronics and communications options. lIbid. 2M. E. Van Valkenburg, "Electrical Engineering Education in the U.S.," IEEE Transactions on Education, E15, 4 (November, 1972), 242. 26 Van Valkenburg named additional important fields (increasing in quantity) like: automation (or cybernetics), nonlinear theory, information theory, millimeter tubes, plasmas, transistors and other solid state devices, radio astronomy, quantum electronics, bioengineering and computer science. One of the important curriculum elements is the laboratory. Professor Van Valkenburg wrote in this regard: Laboratories have traditionally followed cook- book procedures. We have not enjoyed a tradition of interesting and valuable laboratory experiences. Pro— ject laboratories, with considerable student flexibil— ity and initiative, have been slow to develop.1 His more general comment was: "We should give increased attention to educational techniques."2 The development of electronics industries has taken place in many countries besides the United States, especially during the last two decades. Such development, however, is impossible without adequately trained technicians and engi- neers. The November, 1972, edition of the IEEE Transactions on Education is a special issue on international engineer- ing education.3 Robert C. Winton, Chairman of the Manpower and Training Advisory Committee of the Electronic Engineering g lIbid. 2Ibid., p. 243. 3The interested reader may find in this edition of the IEEE Transactions on Education a very interesting reView 0f electrical engineering education in the United Itheindia Scandinavian countries, the United Kingdom, Aus ra i , , Japan, and Latin America. 27 Association in England, described how the Industrial Train- ing Act, enacted to raise the quality and quantity of training in the United Kingdom, is implemented. He out- lined some training recommendations in the electronic and electrical industries.l Great emphasis on cooperating with related industries in training provides relevant subject matter. Unfortunately, in many countries, including the United States, there is little contact between industry and universities. Electronic Circuits Laboratory Experiments-- Past and Present In the 1940's, the lab experiment began to play an integrated role in the electronics curriculum at the tech- nical school and college levels. Most of the lab manuals edited by many manufacturers of electronic equipment intended for training purposes were written in "cookbook" style. Unfortunately, in most cases both the hardware and software have not been student oriented. Schulz, Anderson, and Leyer published a laboratory textbook for college—level courses in electronics, communi- cation networks, basic radio and television circuits, and Q Q h | 2 0 transmiSSion systems including antennae. Concerning the 1Robert C. Winton, "Some Aspects of Industrial Training in the U.K. and Their Impact on Education," IEEE Transactions on Education, E-lS, 4 (November, 1972), 205-211. 2 E. M. Schulz, L. T. Anderson, and R. M. Leyer, Experiments in Electronics and Communication Engineering (2nd ed.; New York: Harper & Brothers Publishers, 1954). 28 purpose of laboratory work, the authors stated: Familiarity with laboratory equipment is as essen- tial to an electronic or communication engineer as an understanding of the theory behind the equipment. This familiarity can be gained only by working with the equipment in the laboratory. The student should keep the following objectives in mind in any engineer- ing laboratory course: 1. To become familiar with the equipment and its behavior. 2. To become familiar with standard methods of tests and Operation. . To learn to work with tools and equipment. . To become familiar with practical considerations which prevent a circuit from behaving as a thioret- ical treatment might indicate that it should. 3 4 The usual procedure of implementing an experiment in electronics has been, and in most cases continues to be, as follows: The instructor assigns a topic for a forthcoming lab experiment and hands out some brief description of the circuit and preliminary work. A week later, when time for the experiment comes, the students construct the circuit (or get it already assembled on a board) and begin to experiment by turning knobs, pushing buttons, and recording data. The student has to fill out a report including experimental pro- cedure, measured data curves, and sometimes answers to spe- cific questions concerning the circuit. Usually, the students work in pairs with one set of equipment. When three or more students are working together on the same experiment, the efficiency of experimentation turns out to be quite low. In these situations, a “job lIbid., p. l. 29 distribution" is Often established; e.g., one student reads the instructions from the lab manual, another turns the knobs, and the third records the data. Evans' book, Experiments in Electronics, consists of 100 experiments on 50 different subjects, most of which are in the "circuits" area.1 The pattern of the experiment procedure is similar to the experimentation procedure des- cribed. The procedure mentioned assumes responsible lab instructors who make the necessary arrangements to keep the lab equipment in Operative condition, maintain a current check on the student's prelims and reports, supply "theory sheets" when necessary, and assign adequate readings for the upcoming experimental topics. An important problem for the instructor is the synchronization between lectures on theory and lab experiments, e.g., to make sure the student has already been acquainted with the circuit with which he is going to experiment. After nine years' experience in instructing and supervising in technical institutions at the junior college level, the writer cannot state that the circumstances are always such as to satisfy these assumptions. During the past decade, laboratory work has assumed a much more important role in many technical schools and engineering colleges. Instructors in electronics and ¥ 1W H Evans, Experiments in Electronigg (Englewood Cliffs, N. J.: PrentiEé—Haii, InC-. 1959). 3O electrical engineering faculty members have spent a large amount of time and effort develOping new programs and lab- oratory facilities. The laboratory experience at the college level may be divided into three major levels: introductory, inter- mediate, and project. The student is first introduced to the basic skills necessary to use electronic instrumentation and equipment and use a variety of measurement techniques. The intermediate laboratory work exposes the student to a variety of electronic circuits, their operation modes, and factors affecting their performance. At this stage, the student is given an opportunity to explore and see if he wishes to enter a given technical area. The laboratory PUDject enables the highly motivated students to attack sane.challenging professional problems. A special issue of the IEEE Transactions on Education was dedicated to exploring the place of the laboratory in a mOdern electrical engineering curriculum.1 This issue illus— trates many innovative approaches that have been develOped to provide various types of electronic laboratory facilities. It Hdght be worthwhile to look at some of these innovative approaches. Oswald and Sloan described one innovative approach: . . . A senior electronics laboratory at Michigan Technological University which operated for more than a year with 100 students each term working individually \ 1IEEE Transactions on Education, Special Issue on Undergraduate Laboratories, E-l4, 3 (August, 1971), 90-94. 31 on an open laboratory basis. The objectives of the laboratory are to teach theory and practice of experi- mentation and supplement engineering theory presented in the classroom. Students schedule time in two-hour blocks and perform experiments alone without direct supervision. . . . Each student is assigned to an experimental advisor (a faculty member). Senior students from the same course are responsible for safety, obtaining new equipment, and circuit trouble shooting. The authors stated that "student and faculty acceptance of the program has been enthusiastic"; and: This laboratory has increased development of exper— imental skills for all students compared with the tra- ditional group operation. The laboratory has functioned on a small budget with no new equipment in the first year and no increase in instructor time. . . . All the instructor's time is now spent in one—to— one relationship with students or in critical review of student reports, rather than laboratory lecture or trouble shooting in laboratory. In the same issue of IEEE Transactions on Education, Banks presented a paper on the tOpic: "The Junior Electron- ics Laboratory: Opportunities for Invention."3 In this kind of circuit design laboratory, creativity and problem solving are emphasized. Pairs of students design, construct, and measure their project. On an oral examination, they demon— strate the working circuit and defend the design. There are only two weekly scheduled requirements: a lecture on Tuesday lOswald and Sloan, "An Economical Self-Supervised Operated Open Electronics Laboratory," IEEE Transactions W. £244. 3 (August, 1971), 90. 21bid. . 3Banks, "The Junior Electronics Laboratory: Oppor- ‘tunlties for Invention," IEEE Transactions on Education, 18-14. 3 (August, 1971), 86-89, 32 to acquaint the students with the following week's project, and a 20-minute private oral examination given by the lab staff on the previous week's project. The average time a student puts into this project lab is ten hours per week. The students compete in solving the same problem, which has many solutions. This type of laboratory is implemented in the Electrical Science Division of the School of Engineer— ing, Case Western Reserve University, Cleveland, Ohio. The three—credit-hour course involves about 65 students each year. Banks stated that "Many students have credited their working knowledge of electronics to this laboratory program." In a rapidly changing industrial world, much emphasis is placed on thorough and continuous in-plant education and training programs. In keeping with this dynamic development, the training activities in large industrial enterprises are often replanned and reorganized to ensure a current and future professional work force. In fact, training schools in industrial plants might be more up-to-date than colleges. However, it is difficult to review such programs, since these in-plant training schools generally don't report their cur- ricula or methods of instruction. In the United States, The Bell System is considered to have the largest educational institution outside the gov- ernment. Sever (Engineering Director-—Education and Training, .American Telephone and Telegraph Company) and Kotch published an article concerned with The Bell System Center for 33 Technical Education.1 In this article, they discussed, among other things, the systematic course development process based on learning principles such as task analysis, establishment of behavioral objectives, valid evaluation, and computer- aided individualized learning. In their conclusion, they stated: "It is through utilization of a sound behaviorally based course-develOpment system that we can be assured the results of training are effective." Unfortunately, this article was written in general terms, and is not as valuable as more detailed information. The use of the digital computer as a teaching tool is an important educational innovation. The extra dimen— sion provided by the computer is now widely recognized, and its almost unlimited instructional potential is being tapped by many curriculum designers. It is only natural that a profound impact of computers on the electrical engineering curricula is becoming increasingly apparent. There seems to be great potential in Computer-Guided Experimentation (CGE) in the electronics lab. The computer is an extremely efficient tool that automatically provides feedback information about a student's laboratory activities, like the interconnections he makes between the terminals of his experimentation equipment and his settings of instrument dials. The student's experimentation activities can be lSever and Kotch, "The Bell System Center for Tech- nical Education: One Industry's University," IEEE Transac- tions on Education, E-lS, 2 (May, 1972), 103-108. 34 transferred to a time—shared, computer-aided instructional system, so he can get automatic guidance through a lesson in any manner preprogramed by an instructor. Neal and Meller presented a paper dealing with Computer-Guided Experimentation at the 1971 Symposium on Applications of Computers to Electrical Engineering Educa- tion.1 In this paper, the authors reported about ". . . the develOpment, operation, and initial performance of an Elec- trical Engineering laboratory station equipped for Computer- Guided Experimentation." The study was carried out in the computer-based Education Research Laboratory at The University of Illinois, Urbana. Since 1968, members of the CGE team have been devising, programing, and testing lessons in exper- imentation. These activities are based on educational psy— chology, Computer-Aided Instruction (CAI), and experience in laboratory instruction. Neal and Meller described the Computer—Guided Experiment station as follows: This CGE station consists of electronic experi— mentation equipment and a student terminal of the PLATO time-shared computer aided instructional system mounted side by side on a large laboratory table (3'0" x 7'8"). The rack-mounted electronic equipment consists of a dual-track wide-band oscillosc0pe, a square, triangle, ramp or sine wave voltage generator, a constant current—voltage supply and a vacuum tube voltmeter. A general purpose circuit board and various alternate printed circuit boards are equipped with auto— matic terminal sensing connections cabled to connectors that can be plugged in at the front of the equipment 1James P. Neal and David V. Meller, "Computer—Guided Experimentation-—A New System for Laboratory Instruction," IEEE Transactions on Education, E-lS, 3 (August, 1972), 147-152. .. “2’s. Vu‘lv- l g p no . J5 I: ‘Aa p at 5-. fr,» V‘o ENC n.» o. I ' C FRO! §,.. fl ~V~u we: \, . :- QA’YAF.‘ h _ bovE vfiv...»: In. ' ‘ ”"‘ “In HR “"“"Vuyu . .QVA‘ ‘ :‘.:a D", a C in. q 1"“ '=~Ort Cc \ It 'y‘ p‘ n flu ‘La. M 35 panel. The present PLATO station equipment consists of a portable television set and a cable—connected table—top keyset.l The authors of the article included an evaluation of two programed lessons. The results were positive in both the cognitive and affective domains. Regarding community-college level electronics instruc— tion, two significant curriculum programs for a two-year electronics technology course (post high school) might be mentioned. The first is Electronic Technology: A Suggested 2-Year Post High School Curriculum.2 This thorough and widespread curriculum suggests a program intended to educate highly skilled electronic technicians. The program was pre— pared by a team of engineers, industrialists, educators, administrators, and technical Specialists. The second program, a more recent, sophisticated, and updated two-year Electronics Technology course, is the Report of the Electronics Technology Curriculum Development Project, which was conducted by the University of Illinois at Urbana-Champaign in COOperation with seven community colleges.3 lIbid., p. 148. 2U.S. Department of Health, Education, and Welfare, Office of Education, Electronic Technology: A Suggested 2-Year Post High School Curriculum, Technical Education Program Series No. 2A (Washington, D.C.: Government Printing Office, 1969). 3Daniel S. Babb, Project Director, Report of the Electronics Technology Curriculum Development Project (Urbana, Illinois: Department of Electrical Engineering, University Of Illinois at Urbana—Champaign, 1971). 36 The members of the Project Staff and the Steering Committee are electronics instructors, coordinators, or heads of college electronics departments. The contents of this lengthy report include the objectives and philosophy of the project, and subject matter for the core courses of an Electronics Technology Curriculum with recommended instruc- tion techniques, facilities, equipment, and costs. The appendices of the report include detailed information regard- ing summer institutes, conferences, multimedia sources, sug— gested texts, references, and bibliography. Review of Literature on Learning Principles and Instruction Methods Learning Principles The present study deals with the development Of an instructional model for experimentation in the electronics laboratory. The related professional literature has already been reviewed in the preceding pages. Related instructional literature will now be reviewed. Concerning the modern conceptions of learning, Gagné wrote: Many modern learning theorists seem to have come to the conclusion that conceiving learning as a matter of strengthening connections is entirely too simple. Modern conceptions of learning tend to be highly analytical about the events that take place in learn- ing, both outside the learner and also inside. The modern point of view about learning tends to view it as a complex of processes taking place in the learner's ‘ , .'tfiv .. d a I ‘\" cc‘.‘ . “ya-~29“ Us -A..ug . .1" NAAVR‘PH VV'C‘ inv" .6 ll '- 3 SEN V I ”viii. u... I a\ .9‘ .nu st 0 s e LL \h~ a L» .nu FU O +L. nu +» A.» '§ :1 37 nervous system. This View is often called an "information-processing" conception.l According to Gagné, modern conceptions of learning lead to a new View of what instruction is all about. He concluded in this article: In the most general sense, instruction becomes not primarily a matter of communicating something that is to be stored. Instead, it is a matter of stimulating the use of capabilities the learner already has at his disposal and of making sure he has the requisite capa- bilities for the present learning task, as well as for many more to come. Hilgard and Bower stated that learning principles are: . . . summarizations of empirical relationships that hold rather widely, although many of them are not stated with sufficient precision to consider them to be "laws" of learning. These writers distinguished between three orientations of learning principles: the orientation toward S—R (Stimulus- Response) theories, toward cognitive theories, and toward principles from motivation and personality theory. The principles emphasized within SHR theory are: 1. Activity of the learner (his responses). 2. Frequency of repetition--to guarantee retention. 3. Reinforcement-—positive reinforcements (rewards) are preferred to negative reinforcements (punishments). 1R. M. Gagné, "Some New Views of Learning and Instruction," IEEE Transactions on Education, E-l4, 1 (February, 1971), 28. 2Ibid., p. 30. 3Ernst R. Hilgard and Gordon H. Bower, Theories of Learnin (3rd ed.; New York: Appleton—Century—Crofts, 1966 , p. 562. .r— ‘6‘) (I) L" o r l ‘5- H 38 4. Generalization and discrimination—-learning becoming apprOpriate to a wider range of stimuli. 5. Novelty in behavior. 6. Drive conditions--motivational conditions are impor- tant. 7. Conflict and frustrations—-irrelevant motives have to be recognized and their resolution or accommoda- tion provided for. The main points of several related theories of learn- ing will be pointed out next. According to Bruner's theory of cognitive develOpment, there are three ways of knowing: (l) enactive--through doing, (2) ikonic--through seeing, and (3) symbolic--through a symbolic means.1 Bruner also formulated three levels of thinking: concept formation, interpretation of data and inference, and applications of principles. In 1960, Bruner propmsed the spiral curriculum to identify basic concepts and prdJmciples of a discipline, and to teach at increasing levels <1f difficulty (sequential and cumulative). In Gagné's hierarchy of learning model, eight learn- ing categories are arranged in order from simple to complex. 'Fhis hierarchy is based on the assumption that each higher «order of learning depends upon the mastery of the one below .it. The eight types of learning cited by Gagné are: 1J. S. Bruner, "The Act of Discovery," Harvard Ekmicational Review, XXXI, l (1961): J. S. Bruner, Toward Efflrheory Of InStIUCtiOD (Cambridge, Mass.: Harvard Univer- Eity Press, 1966) . 39 1. Signal learning--a general response to a signal. 2. Stimulus-reSponse learning--a precise response to a discriminated stimulus. 3. Chaining——linking several responses by reinforcing the responses done in sequence, continuously increas- ing the number of responses linked together. 4. Verbal association--learning of verbal chains. 5. Multiple discrimination--n different identifying responses to n different stimuli. 6. Concept learning--acquiring the capability of making a response that identifies an entire class of exper- iences, objects, or processes. 7. Principle learning--describing relationships between events to be used for prediction. It may be ver— balized in a rule form like: "If A, then B" where A and B are concepts. 8. Problem solvinge-a strategy from problem sensing and formulation to the search and implementation of a solution. Requires thinking to combine two or more . . 1 prinCiples. Skinner's reinforcement theory is based on the fol- low ing principles: 1. Operant conditioning--first respond, then reward. "Operant" is a behavior which changes frequency as a function of its consequences. __~_~§__ lHilgard and Bower, op. cit. 4O 2. Information is best assimilated in small steps. 3. Student should be actively involved in the learning process. 4. Immediate reinforcement of correct answers. 5. Self-pacing.l According to Mager's theory of behavioral objectives, a behavioral objective is a precise description of the beha- vior (visible or audible action) a student is expected to exhibit after instruction under specified testing conditions and standards for adequacy of performance.2 Thus the beha— vioral Objective has three factors: 1. Behavioral term (measurable). 2. Conditions under which behavior is to occur. 3. Criterion of acceptable performance. Mager once commented, with reference to objectives: "If you don't know where you are going, you are certain never to get there." Mager's main points concerning learning in general are: 1. Focus student attention. 2. Achievement is increased when teachers and students understand objectives. 3. Emotional atmosphere is improved if more pleasant 1B. F. Skinner, "Why We Need Teaching Machines," Harvard Educational Review, XXXI, 4 (1961); B. F. Skinner, "The Science of Learning and the Art of Teaching," Harvard Educational Review, XXXIV (1967). 2 R. F. Mager, Preparing Instructional Objectives (San Francisco: Fearon, 1962). 41 emotional reactions are elicited and more time is used in helping students deal with emotions.l Taxonomy of Educational Objectives The two domains in the taxonomy of educational objec— tives are the cognitive and the affective domains. Cognitive behavior is internal, unseen behavior, including thinking. It usually takes the form of problem solving and conceptual or verbal behaviors. The main aspects of cognitive domain are: knowledge, comprehension, application, analysis, synthesis, and evalua- tion.2 Affective behavior is neither related to verbal pro- cesses nor to skilled action. It is emotional behavior. Affective behavior may be expressed by persistent approach or avoidance in reference to a particular set of events. The main aspects of the affective domain are: recep- tion, response, valuation, organization, and characteriza— tion.3 These factors may be regrouped as personality com- ponents: interests, attitudes, and values. 1R. F. Mager, Speech before the 1970 Convention of the National Society of Programmed Instruction, Anaheim, California, 1970. 2B. 8. Bloom, et al., Taxonomy of Educational Objectives (New York: David McKay, 1956). 3D. R. Krathwohl, et al., Taxonomy of Educational Objectives, Affective Domain (New York: David McKay, 1964). : "‘n. An‘ I U.Vv:( :A n‘pr‘...“ o: Duvn.. ‘ .IIFVHAf‘ . out: a. MN: y- _ .‘Y ;n .ci" 'V h su¢uu H I . .A .- " ' “""~c EV N.\'~-"‘ P' ‘0‘ . d . PIA“ ‘ ““ “flea . w b P“ . ‘1‘." thy.“ ‘ ‘ “su ”A .‘~ th_Q;i1t * ‘w' «:51: exvq V . H ‘ O"a‘ 42 As a conclusion of the review on learning principles, a "block diagram" presentation of the Hierarchy of Knowledge is shown in Figure 3. Instructional Methods After briefly reviewing the current literature on learning principles, it seems to be reasonable and logical to proceed with a review of literature regarding instruction methods related to this study. Three areas were searched: individualized instruction, programed instruction, and audio-tutorial instruction. Individualized instruction.-—The idea of individual- izing instruction is not new. Plato, in his Republic, mentioned dueneed for recognizing individual differences in learning. In modern times, several people have pointed out the need to individualize instruction. White indicated that only through individualized instruction can appropriate lessons be given for each learner, and thus minimize the possibility of increasing students' problems through unreal- istic expectations and demands.1 Many voices have been heard in favor of individual- ized instruction, but at present not many courses fulfill this Objective. Wilhelm pointed out that: . . . The common grouping system will tend to hold two kinds of danger. First, there is a danger of stereotyping. With reference especially to the sec- tioning of classes into ability groups it is notorious lVerna White, Studying the Individual Pupil (New ‘York: Harper and Brothers, 1968), p. 12. SJCLST... -~,..~.-v.4>.-u:q. 4.2:; CTLK 11!. CZ i Z :<..._.H 2C E.E./2.. a Z 2 1.07.4 2 43 mo mmoaaoo . pom poaaflxm cwumcflcuooo .ucwsam Euomumc cmo .Hsaa .sunuuu>flqs mumum ummnaoflz .conumosum .mmwwHSOGM mo accumuwfimln.m wusmflm HwaofinsHom 3mg ocflm fimmg mm. weH>Heammo . mcofludaom usmeHmEH can scan uuo OZH>QOm qumomm ancnoms can : ammo HmcowuosuymcH .conw .q cosmoum Eoum corms "condom UZHZMémA AAHMm moocmscwm pocflmco Usuouoe EuOMme cmu OZHZHflmU mEmHQoum mcfiumflxm use ucflom cmu UZHZMémq NMHDOZH muomw wumum GOO UZHzmm cmm3umn mmflcmcoflumHmu on mcflcuooom EHOMHOQ can poapwum cmo OZHZMde mquUZHmm mono oamfiuasfi Auwumav cam wamcflm co Ommmn mucw>m HMSOH>AOGH Honma cmo 1 mumm use ucflom cmo UZHZMdMA Emmozoo UZHzmémq ZOHB2. 2 2“ ~\» H. ~ Cu h« .a .C .- .— .pu .nu NJ. 6.. Cs» .M-. -n r» ..u Av wk 0- v. n- ~. 6» . us.s ~.Hn‘w 48 out the detailed design. After design work comes prototype testing, revision, and then field testing before produc— tion.1 The power of any programed learning is based on a student's active response to the designed sequence of items. The authors are highly in favor of programed learning. As they stated: The claims made for programed learning are many. In our experience they are mostly true. Students using programed materials have been able to perform very well. Each is able to work at his own pace, review as much as is needful and be confident of his results. . . . For the teacher the advantages have been considerable reduction in routine work and a certainty of a reasonable performance by the students. . . . Those of us who have used it, both as stu— dents and teachers, are convinced that programed in- struction is the most effective educational tool yet devised.3 As to the use of programed instruction in the elec— tronics laboratory, one experimental study carried out at the University of Illinois, Urbana, involving programed learning has already been discussed on pp. 33—34 of this chapter.4 lHelen L. Plants and Wallace S. Venable, "Programed Instruction: An Application of the Engineering Method," IEEE Transactions on Education, E—14, 2 (May, 1971), 41-44. 2Plants and Venable are with the Department of 'Theoretical and Applied Mechanics, West Virginia University, Dkorgantown, West Virginia. 3Plants and Venable, op. cit., pp. 43-44. 4Neal and Meller, op. cit. 49 Roth reported about utilizing programed instruction to teach use of the oscilloscope in the junior electrical engineering laboratory course at the University of Texas, Austin. He wrote: A programed text was developed that breaks down the process of Operating a scope into a series of logical steps starting with deflection of the elec- tron beam. . . . Results from practical examinations and observa- tion of student performance in later courses indicate that students learn to use the oscilloscope more effec- tively from the program than from conventional labora- tory instruction. Audio—Tutorial Instruction In the present study, the researcher has tried to utilize modern instructional methods as well as modern hardware to enable a student to achieve optimum results from his lab experiments. That is the reason for a student- oriented audio-tutorial approach. In this study, audio- tutorial technique of instruction means the use of audiotape and slides in conjunction with presentation of the subject Inatter concerning the circuit under experiment. One of the important pioneers in the field of audio- tutorial instruction is Professor S. N. Postlethwait from ZPurdue University. At the very beginning of Postlethwait's xvork, the following statement appears: A fundamental guideline which must be given prime consideration is that "learning is an activity done 3Charles H. Roth, "Programmed Instruction for Use (of the Oscilloscope," IEEE Transactions on Education, E-14, ,3 (August, 1971), 138. 50 py an individual and not something done to an indi- vidual." The structuring of an educational system should be done on the basis that the program must involve the learner. The teacher at best can only create a situation conducive to learning by providing the direction, facilities and motivation to the indi- vidual learner. Immediately, it becomes apparent that the program must allow for individual differences in interests, capacity, and background. Some of the activities that result in learning in an informal situation (as in the audio-tutorial case) are: l. Repetition. 2. Concentration. 3. Association (involve maximum senses during the learning experience through association). 4. ApprOpriately sized units of subject matter. 5. Use of a communication vehicle apprOpriate to the objective. 6. Use of multiplicity of approaches (multi-media). 7. Use of an integrated experience approach.2 In the conclusion of their work, the authors listed the advantages of the audio-tutorial approach: 1. Emphasis is placed on student learning rather than on teaching. 2. Students can adapt the study pace to their ability to assimilate the information. Exposure to difficult 1S. N. Postlethwait, J. Novak, and H. T. Murry, Jr., 'rhe Audio-Tutorial Approach of Learning Through Independent Study and Integrated Experiences (2nd ed.; Minneapolis: iiurgess Publishing Company, 1969), p. 1. 2Ibid., pp. 3—4. 1 J 10. ll. 51 subjects is repeated as often as necessary for any particular student. Better students are not a "captive audience," and can use their time most effectively. Their inter- ests are not dulled by unnecessary repetition of information already learned, but they are free to choose those activities which are more challenging and instructive. The student can select a listening time adapted to his individual efficiency peak. Tapes demand the attention of the student. Students are not distracted by each other. Students have more individual attention, if they desire it. Scheduling problems are simplified. The four hours of scheduled time from which the students are relieved under the new system can now be distributed throughout the week as necessary to adjust to the students' activities. More students can be accommodated in less laboratory space and with fewer staff. Make—up labs and review sessions can be accommodated with a minimum of effort. The student feels more keenly his responsibility for his own learning. Each student is essentially "tutored" by a senior staff member. 1»- p u R\~ .mq :2 .ra a». a n» .. u a». a». 4 t as ‘5. v .. .h 5 52 12. Opportunity for research on learning processes is enhanced.1 The audio—tutorial approach makes use of the learning principles mentioned earlier in this chapter (i.e., those of Gagné, Bruner, and Skinner). It can be used to achieve behavioral objectives (Mager) at any level of the three domains: cognitive, affective, and psychomotor (Bloom, Krathwohl). This concept of learning stresses the need for providing optimum conditions to achieve the maximum develOp- ment of each individual's learning capacity. One of the recent developments in audio-tutorial techniques is the Minicourse, a self-contained unit of instruction that tutors a student through an integrated experience and Optimizes the conditions for learning. The instructional package deals with a single unit of subject matter. The minicourse usually involves portable materials, so the student can carry out the learning process in the library, study carrel, or at his residence. Development of minicourses has been carried out at Purdue University, Lafayette, Indiana. The minicourse appears to be the unit (or module) through which various subjects will be learned in the future. The great flexibility lIbid., p. 96. 2James D. Russell (Minicourse Project Coordinator, Purdue University, Lafayetter Indiana)' "A.SYSte§::§:ntsu Approach for Developing minicourses for Selenfiers Associa— (paper presented at the National SCIence Teac e tion Convention, Washington, D.C.: March 29: 1971). 53 of the minicourse may be the main factor of its potential applications in the ever—changing circumstances of modern instructional needs. The audio-tutorial approach of instruction was begun in the early 1960's. The approach was originated in the botany field, in an attempt to make some adjustments for the diversity of student backgrounds in a freshman botany course. Most of the study reports at the Third Audio-Tutorial System Conference were in the field of biology; only two presenta- tions out of 39 were from the electrical field. Rainey presented an audio—tutorial method in elec- trical and electronics laboratories that is being applied in the Department of Electrical Technology at Purdue Univer- sity.1 Audiotapes, color slides, and other audio-visual materials that are supplied to the students enable self- paced, individualized instruction in electrical and elec- tronics technology. Some useful points of this experience given by Rainey are: Slides and tapes used in the audio-tutorial method do not take the place of the instructor, but free the teacher to teach! Students obtain the technical information and instructions from the audio—tapes and slides, which leaves the instructor free to work with the students on real problems. . . . The control of th instructional materials, free- rationalize most electronic circuits, because there is 'usually a reason for the existence of a practical circuit. Referring to the hierarchy of knowledge (page 43), tflxis strategy is an example of "Inquiry," pointing out exjjrting problems, and "Problem Solving," trying to find 1Appendix A, p. 139. RA buy an» ‘4; Rflfll‘a‘ an-Vy: l a... .‘ ‘ “"‘6-1 I 5":- 5“. 'f I. In 65 adequate solutions. Lower steps of the hierarchy of knowl- edge must be fulfilled too. For instance, in the case of the Schmitt Trigger, the student has to master electrical and basic electronic circuits,devices and theory including concepts and principles; if he doesn't, remedial material must be provided to help him fill some "knowledge vacancies." Only after mastering the prerequisites should he proceed with the experiment. An example from the writer's experience may demon- strate the damage caused by nonfulfillment of the prerequi- site requirements. The concept "Loop Gain" was not clear to many students, and this caused difficulties in under- standing the experimental process. Mastery of this concept by the students shouldn't have been taken for granted, even if the "try-out" student was vaguely familiar with this concept. A good idea might be to administer a special pretest to check a student's degree of mastery of the prerequisites. This pretest should be taken enough in advance of the exper— iment.(more than a week), to enable the student to Obtain rxunedial help. The student should be provided with adequate remedial material. The Theory Sheets include the following main items (Appendix.A): 1. Purpose and behavioral objectives. 2. Rationale to provide a functional view through practical application examples. 66 3. Generalized qualitative analysis of the circuit under experiment. 4. Specific quantitative analysis of the circuit. 5. Summary of the circuit analyses and some relevant remedy notes. 6. Examples of various versions (transistorized, inte« grated circuit) of the circuit. 7. Practical application examples of the circuit. 8. Detailed solved problem which includes the circuit and the results of the above analyses. 9. Preliminary work including precalculations of some of the components and values that are going to be measured during the experiment. This is one of the problem-solving tasks in which the learner is to find and implement solutions which will be used as compar- ison to the forthcoming measures in the laboratory. The Specific quantitative analysis of the circuit (item 4) is the longest section in the Theory Sheets. Those students who have already mastered the circuit theory may skip this section. Tflua.Experiment Procedure Sheetsl The Experiment Procedure Sheets constitute the second portion of the laboratory manual. They include systematic laytnit of the experimental procedure using flow charts and 1Appendix B. 67 comments. The advantage of the flow chart is in getting an easy, immediate overview of the procedure. An example of a generalized initial portion of an Experiment Procedure flow chart is shown in Figure 4. The numbers in some of the blocks in this diagram refer to cor- responding checklists and notes. Such a specific flow chart with the checklists for the Schmitt Trigger experimental procedure is shown in Appendix B, Figure 1. Referring to Figure 4, the various blocks will now be interpreted. Eptg£.--Regarding the circuit under experiment, there are two possibilities of "enter" status: 1. A student is given all the materials and components except those "missing components" which he has to determine by himself in the prelim work. He has to construct the circuit according to the given Circuit's schematic diagram and start experimenting. This is usually the procedure in technical schools. 2. A student is given the practical circuit already mounted on a board. Those components he has to determine by himself are missing. This procedure is used mostly in engineering colleges. In either case, at the "enter" stage a student is provided with the necessary tools, equipment, and media sources to enable him to carry out the experiment. The equipment is usually assembled at the working station. All sorts of media may be used: 68 «ems aw mxms oeoanm .musumooum wnfiucwfiaummxo =:0wumnmmo mumumumanmum= mamsamc< .o.< on wan newuosuouuanl.v munmwm uwucm 1| llllllllll ll lllllllll ll llllllll l||l1 llllllllll _ \P/ _ BHZD wzHBoomm mqmnoma . _ m..~. _ _ mucwcomaou \J. _ mucmESMumcH mcofluowccoo mucwcomEoo. m>wmmmm m rH\ Iv _ a mommuao> Hauuau xuwnu w>wuo< umma whammmz :OHDHUGOU _ hammsm x0050 a xumnu manmum pmuommxm _ now 02 _ “ m.x.0 _ .dEoo mm» _ _ oz Ammv _ mosam> wanmuw _ muumucoo usmcomfiou ucmcomfiou pmuowmxm _ Hammwm wumHmmm monammm ou mummEOU _ >9 womHmmm _ ¢ _ IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII L Ame Ave Amy Rama ”Na sewumummo A_>uflumaom wmmuao> >amm3m A.U.Ov 11L cocoa mumumz a HouosuumcH 39H: .mu:m:0QEou Macmilwuasz mumum magnum mmfisom.o.a.mucm >umnueflaoum mo mcflmmaz :msoune mudmmmz .COQEOU uomzcoo muasmmm xowno mumHDoamu noun: a :muqu Anne ammEmm a mad: m.uou nosuumnH umw 69 Printed (texts, journals, study guides) Graphic (charts, graphs, diagrams) Pictures (flat, film strips, slides, film loops) Audio tape player (and tapes) Films, film loops Television (monitor) Video tapes Realia (an actual circuit or model) Computer terminal Electronic calculators Electronic instrumentation (an oscilloscope) Which media to incorporate is contingent on the cir— cumstances; primarily budget considerations. However, this model may be implemented with a very low budget for media equipment in addition to the regular electronic instrumen— tation. In the eXperimental test of this study, the cost of the additional media station for two students, including audio tape player, slide projector, projector Viewer, and two headphones, runs about $180. Listen & Watch Through Multi—Media.——The importance of increasing a student's involvement in the experimental process was stressed earlier in this chapter. It was also stated that stimulating a student's interest in the circuit 'will contribute to an increase in his active involvement. The learner, as every living creature, is stimulated through his senses, so it seems reasonable to appeal to as many senses as possible during the learning process. The 70 multi-media approach may be used as an efficient communica- tion Vehicle, because it enables involvement of more than one sense during the learning process. In the stage of "Listen & Watch Through Multi-Media," a student may use media facilities to proceed at his own pace through a detailed analysis and application of a cir- cuit. In essence, it is the same analysis as in the Theory Sheets, but more applications and audio—visual explanations can be provided through a slide~tape or video tape presenta- tion. In this study, a slide—tape presentation was used. To get a learner's attention and involvement, the introductory pictures or slides of the presentation must consist of concepts (objects or processes) with which the student is already familiar and, if possible, which cause pleasant associations. Next the presentation proceeds toward the subject matter itself: analysis, problem solving, and at the college level the highest level of knowledge is reached—~namely, creativity-~where the learner is capable of finding new solutions for a given problem. For the first slide in the slide—tape presentation in this study dealing with the analysis of the Schmitt Trigger, the researcher selected a color picture from a weekly jour- nal showing street lights in a Texas town. Through this Slide, the student is introduced to the problem of Automatic Street-Light Control. The second slide shows the block diagram of the twilight switch (Appendix A, Figure 1). It Should be noted that the student is familiar with all the 71 items shown in this block diagram, excluding the new concept (the x block, which is going to be investigated). The learner is getting to know the problem in a sequence of small steps, so when the "solution" is presented, e.g., the Schmitt Circuit itself, he is more likely to accept it and try to understand its functioning. It is the belief of the researcher that this gradual introduction to the analysis of a circuit contributes more to a student's involvement in the learning process than exposing a learner to the schematic diagram right at the beginning of the circuit analysis. Experimental research has to validate the researcher‘s beliefs. The multi—media may also be used for modeling1 pur— poses, eSpecially when the experiment involves complicated performance. A good model includes verbal explanations at the time the model is demonstrated. Not only can the instructor demonstrate some important portions of the eXper- imental procedure, but a video tape, film loop, or even slide-tape presentation of the modeling may provide a stu- dent with repetitive self—paced Opportunities to check out ambiguous points in the experimental procedure. The serious instructor can always update the cir— czuit's applications by videotaping new develOpments from ——— lA. Bandura, "Social Learning Through Imitation," in Iflebraska Symposium on Motivation: 1962, ed. by M. R. Jones 'Ciincoln: University of Nebraska Press, 1962), pp. 211-269; 1;. Bandura, "Vicarious Processes: A Case of No—Trial Learn- jJug," in Advances in Experimental Social Psychology, II, ed. IQY’IH Berkowitz (New York: Academic, 1965), pp. 534-536. h..- .— tn.» ‘a v... "Fry. V|I\.\ ‘w n“- v»- ‘~\.. V», “a (I! l f 72 industry or laboratory, or adding new slides with adequate explanations. It might be fair to a student to let him use the multi—media phase of analyzing the circuit as an option. If the student enters the laboratory after he has studied the theory and applications of the circuit and has correctly prepared the preliminary work, he is eligible to skip the stage of "Listen & Watch Through MultinMedia" and start the experimental work on the circuit. Most students will choose to use the media, if it is incorporated with meaning— ful and understandable explanations so they can benefit from it. Proceeding with the blocks in the flow chart (Figure 4), the following procedures will be carried out: Calculate Missing Components and Supply Voltag§.~— This calculation is a part of the preliminary work. If a student has not completed his work at home, he has to do it in the laboratory after studying the Circuit's theory and applications with or without the aid of media presenta— tions. Check Results of Preliminary Work With Instructor.—- Therezare two main reasons for an instructor‘s check of a student's status at this stage: 1. To find out if a student has acquired the essential prerequisites (knowledge and skills). 2. To check calculated values of the missing components and supply voltages, and to make sure that these 73 values will not cause any damage or endanger the student when applied to the circuit. Get Instructor's Help & Remedy.--If an instructor finds out from the preceding step that a student doesn't meet the required prerequisites, he has to guide the learner to remedial sources and facilities. It is strongly recom- mended that these sources be available inside the laboratory where the experiments are carried out. The remedial mate- rial should include the electronic equipment manuals (for operating equipment), as well as textbooks, handbooks, dia- grams, and catalogues. Varied forms of media may be used for this remedial learning purpose. If the instructor's monitoring is eliminated for any reason during this stage, the student should be given safe component and voltage values. Connect Components, D.C. Sources & Meters.--After having checked the correctness of calculated values of miss- ing components and supply voltage, a student may connect all D.C. sources and instrumentation (according to a (detailed checklist) and activate the circuit. Measure Stable State (D.C.) Operation.--A student <:arries out a series of Direct Current (D.C.) measurements eat various points of the circuit determined by the instruc— ‘toru These points are listed in a table which includes the cualculated and expected values of voltages. This is done fcn: comparison purposes (5a in Figure 4). Such a table :forr the Schmitt experiment is shown in Appendix B, Table l. 74 This procedure provides natural feedback for the student concerning his predictive calculations. In case the circuit under experiment has no D.C. stable state, like an oscillator, the student may skip this step (5) and proceed directly to the next step, which involves A.C. measurements. What if the circuit malfunctions? The traditional approach to answer this problem is to ask for an instructor's help. But if all the students having trouble with the cir- cuit (which could be a large portion of the group working in the laboratory) called for the instructor's aid, he would be too busy to supply all the help necessary. This is usually the case if the students and instructor really care about what is happening in the laboratory. Why shouldn't the student carry out some trouble shooting in the circuit by himself before he calls for an instructor's help? In order to assist the student to help himself, a trouble shooting guidance unit is suggested. Trouble Shooting Unit.--Trouble shooting is the pro- <:edure for finding the exact location of and reason for the :factor causing malfunction of a piece of equipment. This }m wm.av wm.mv wm.ma no moma.o mmoa.m mmmv.o memo.a mw.ma ma.>m mm.ma mm.mv mo mmmo.o aama.m mmmm.o mmmh.m mm.mm mv.m ma.an mm.m mo nmmo.o ommm.m oamm.o aama.m mm.m mm.nn wm.m wm.mm so Nnmm.o voma.a moqm.o wmmo.a mn.ma ma.mm mm.mm wa.am mo mmmh.o mama.o mmmm.o osmo.o wm.m wm.mm wv.v $0.0m mo Homo.o mmom.v ovmm.o owmm.m wa.aa mm.m> ma.aa mn.mv Ho swap mmma m oflpmm m .Om one: .qm one: am HO O mm no a now HO O 64m no 4 soflpmmso Genoa: cmmzumm monouo unmaummue mmsouo comflummeoo moccanm> mo mammHmcs mumflnm>fico mumzmsm .mncmpsum mo soapsnuppmao .Ammoonm GOmHHmmEoo .m> psmEummnuv muHSmou «>024 onwanw>fiss cam mn03mcw moonfluum osmosum mo ceausoflunmaonu.m magma 112 MSU, while 11.1 per cent are dissatisfied with this method. The remaining 42.2 per cent of the students in the comparison groups answered "Neutral" to the first question. In the treatment groups, 76.2 per cent would prefer to use the suggested model of experimentation in the future, while 11.1 per cent would not. The univariate analysis of variance on this question resulted in significant difference between the treatment and comparison groups (p<0.0301) in their willingness to continue experimenting by the same method they used in this experiment. Q2: (23: Q4: A vast majority of the students (80%) in both categories (treatment and comparison) admitted that calculating the expected values to be measured before the experiment made the experiment more understandable and interesting. 51.1 per cent of the comparison group members stated that the conventional experimental procedure enabled work without waiting for the instructor, while 28.9 per cent of these groups claimed that this procedure had not enabled self—help. In the treatment groups, 65.1 per cent were positive while only 12.7 per cent were nega— tive in this matter. No statistically significant dif— ference was found between answers to this question by treatment and comparison groups. 68.9 per cent of the comparison group students felt a positive reinforcement in knowledge and interest in switching circuits (the category of electronic circuits Q6: Q7: was: 113 to which the Schmitt Trigger belongs) as a result of working on the Schmitt experiment, while 8.9 per cent of these groups did not have such a feeling. The cor- responding distribution of the treatment groups' answers to this question was 77.8 per cent positive and 3.2 per cent negative. The weight of the various answers to this question was reversed in the univariate ANOVA; e.g., SD+SA, D+A, N+N, A+D, and SA+SD, because this question is stated in a negative way. The results of the ANOVA analysis regarding this question indicate that more comparison group members fol— lowed the experiment procedure without understanding it than did the members of the treatment groups. The significant difference was at the p<0.0258 level. 57.1 per cent of the treatment groups' members felt more confident being able to deal with the Schmitt circuit after experimenting on it, while 42.2 per cent of the comparison groups felt the same way. The greatest significant difference (p<0.0009) appeared on the answer to this question, indicating that more members from the treatment groups than those from the comparison groups felt they had learned more from this Schmitt experiment (using the model) than from any other experiment in electronics so far. The null hypothesis regarding the affective domain There will be no difference in the positive attitude 114 of the students toward the method of experimenting with electronic circuits, between the treatment groups and com— parison groups. In order to investigate this general hypothesis On the basis of the Attitude Test's outcomes, a multivariate analysis of variance was carried out. The results are pre- sented in Table 10. The mean scores of the treatment and comparison groups on all the seven questions in the attitude test were employed, using the Finn program. Table 10. Multivariate attitude ANOVA. Multivariate Source F Ratio D.F. p less than Treatment vs. Comparison Groups 2.84 1,64 0.012 Treatment Groups Difference 1.11 28,232 0.329 (Zomparison Groups fiDifferenoe 1.18 28,232 0.248 The decision was to reject the null hypothesis. The <:onc1usion is that there is a significant difference (p<0.012) in the positive attitude of the students toward the method of experimentation with electronic circuits, between the treat- Inent groups and comparison groups. This indicates that the members of the treatment groups held a significantly more IXDSitive attitude toward experimentation by means of the “KNm31 than members of the comparison groups held toward eMperimenting through the conventional method. r'vmrn 115 It can be seen in Table 10 (treatment and compari- son groups within results) that some homogeneity exists among the treatment groups' attitudes toward the model, as well as among the comparison groups' attitudes toward the conven- tional method of experimentation in the electronics lab. Three additional questions were submitted to the members of the treatment groups on the Attitude Test form (see Appendix D3). The answers of the students were distrib- uted as follows: QB: 46.1 per cent of the treatment groups' members stated that the flow charts describing the experimental proce- dure had helped in proceeding by themselves while work- ing on the experiment; 15.9 per cent of the students disagreed with that. Q9: 57.1 per cent of the treatment groups' members admitted that the slide-tape presentation of the Schmitt circuit had been helpful, while 22.2 per cent had had no benefits from this medium (according to their own statements). 010: 44.5 per cent of these students would like to have addi- tional slide-tape presentations of the Schmitt Trigger applications, and 19.1 per cent were opposed to having additional presentations. It seems that a certain learning aid which is good fCu? one student is not necessarily good for another; there- fOre, the student should be given alternative learning aids 533 he can choose the one that best fits his personality. 116 The Instructors' Evaluation of the Model The instructors of the treatment groups were asked to fill out a form concerning the application of the model during the laboratory sessions they had monitored (Appendix D4). Here are their answers: 1. All three instructors chose not to demonstrate the circuit Operation to their groups. 2. All of the instructors stated they had not been occupied with students' problems during the experiment, any more than in the usual electronic lab experiment. (It has .to be kept in mind that these instructors were not profes- sionals; they were graduate students.) 3. All instructors reported no lack in student prereq- uisite material. 4. Vagueness of the lOOp—gain concept was mentioned as difficult for students and instructors. 5. One instructor introduced remedial material, just for one individual. The other two did not introduce any remedial material. 6. Two instructors preferred to use the suggested model rather than the "classical" method of experimenting with electronics circuits. The third instructor stated that the use of the model depends on the specific objectives desired. 7. It was the writer's perception that the instructors' attitude toward applying the model, although reluctant and C001 at the beginning, became warmer and more positive as 117 the experiment went on, during the two—week experimental period. Summary The statistical analysis of the study has been pre- sented in this chapter. Measures in the students' cognitive and affective domains were carried out and analyzed using the computer facilities at Michigan State University. Instructors' attitude toward applying the instructing model in the electronics laboratory was searched and the results presented. The decisions made on the basis of the statistical analysis are listed in Table 11. Table ll.--Statistica1 decisions. 118 For No Difference Source of Between or Comparison p Within Groups (Groups) Decision less than Test Pretest Treatment vs. Fail to Comparison Reject 0.9544 ANOVA Posttest Treatment vs. Comparison Reject 0.0004 ANCOVA Retention Treatment vs. Test Comparison Reject 0.0001 ANCOVA Pretest Treatment Fail to Within Reject 0.9519 ANOVA Posttest Treatment Fail to Within Reject 0.9551 ANOVA Retention Treatment Fail to Test Within Reject 0.2815 ANOVA Pretest Comparison Fail to Within Reject 0.2018 ANOVA Posttest Comparison Fail to Within Reject 0.8130 ANOVA fetention Comparison Fail to Test Within Reject 0.9659 ANOVA Attitude Treatment vs. Test Comparison Reject 0.0120 ANOVA CHAPTER VI SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS Discussion The essence of the development of the instructional model of experimenting with electronic circuits is the audio-tutorial approach. The central idea of the audio-tutorial approach is that the learning activity is done py the student and not t3 him. If a student is supposed to learn, he must be given conditions to do so in the most beneficial manner. The model suggested is an attempt to set conditions in the electronics laboratory which will lead to learning. The elements of the model may be considered as inde- pendent variables. The word "variable" implies that these conditions of learning may vary, so at least two alternative conditions have to exist. Some of the independent variables in a learning system may be: 1. Type of instruction—-lecture-based teaching, indi— vidualized tutorial instruction, programed instruc- tion, or audio—tutorial instruction. 2. Media--presence or absence of media. 3. Types of media employed. 4. Timing between elements-—timing between a laboratory schedule and corresponding theory lectures. 119 120 5. Integration of elements-—integrating theory and lab experiments versus separating them. 6. Student options versus teacher choices. 7. Evaluation based on mastery or on relative standards. 8. Type of evaluation-—written, oral, or performance tests, or a combination. 9. Type of instructor—~in the electronics lab, the pro— fessor in charge of theoretical portion parallel to the lab course, a graduate student, or a professional specialist from industry. 10. Student's choice of time to learn—«choice in experi— mentation time (Open laboratory) versus scheduled procedure. 11. Mediated and live demonstrations—~demonstration of the experimental process by the instructor (modeling) versus demonstration by media or no demonstration at all. 12. Upgrading the program (every year, for instance). 13. Order of presentation and experimentation-—i.e., to start with A.C. measurements and then check the D.C. conditions. The outcomes of the learning process may be labeled as dependent variables. The following outcomes may be con— Sidered variables of this category: 1. Amount of material learned in a period of time (concepts, principles, skills). 2. Degree of student's mastery of the subject matter. 121 3. Degree of student's retention of the material studied. 4. Extrapolation capabilities of the students in apply- ing the learned material to meet needs of the real world (transfer). 5. Efficiency of the instructional method concerning the following components: a. DevelOpment and material preparation of the lab experiments. b. Equipment and laboratory facilities—~investment and maintenance. c. Instructors' time and wages. d. Students' time consumption. 6. Students' attitude toward the learned subject. There are no precise rules or laws which express a quantitative mathematical relationship between the dependent and independent variables of an instructional system. Often it is difficult to identify all the independent variables affecting a set of dependent variables. Since there is no mathematical formula expressing the dependent variable as some function of independent variables, it is practically impossible to find the precise nature of the independent Variable through differentiating procedure as used in cal- Culus. Experimental testing must be employed to determine time approximate relationship between the two types of vari— ailbles. Prediction of outcomes may be made only for those 122 future cases where the independent variables will be similar to those used in the study. For this reason, the sample has to be precisely described. In the experimental testing of the model used in this study, only a generalized search of its instructional potential has been carried out so far. Summary Since electronics has become a factor in everyday life, many peOple face the need of professional mastery in this field, which is abstract in nature. Research and development of instructional methods must be carried out to accommodate students who are interested in this profession. Some experimental studies carried out in this field during the past several years have pointed out the potential of applying modern learning theories in electronics studies to improve instruction. There are eleven main components of the model developed: 1. Preliminary work by a student based on handouts and assigned reading, including calculations of electrical Performance that will be measured in the laboratory experi- mentation. 2. Use of audio-tutorial techniques in the theoret— iCa1.analysis of the circuit and its applications. 3. Use of an oscilloscope as a powerful medium in Studying electronic circuits for scanning the output 123 characteristics, displaying waveshapes at various points in the circuit, or scanning the actual transfer characteristic of the circuit; that is, the output voltage as a function of the input voltage. 4. Use of guides and flow charts describing the experi- ment procedure (optional). 5. Creation of conditions for a student's active involve- ment in the experimentation process-—letting him take part in the "design" of the circuit by calculating some missing com— ponents and providing immediate feedback for reinforcement. Measuring the circuit Operation and getting expected results during the experimental process frequently provides a stu- dent with successful experience; this increases his involve- ment. 6. D.C. (Direct Current) and A.C. (Alternating Current) measurements of the circuit's operation and comparison to precalculated values of voltage, current, or amplification. 7. The use of an experimental analysis of the circuit; a combination of laboratory and theoretical investigation of the circuit's reaction to external or internal changes imposed on it, like changing feeding voltages, loading, environmental circumstances (temperature), or changing the Values of its internal components. If an integrated circuit is under experiment, only external changes are investigated. 8. To keep in touch with the real world, a student is Shownia few typical practical applications of the circuit at this stage; the newly learned details of the circuit are 124 investigated under real conditions. It is recommended that media be utilized for application demonstrations if "live" practical circuits are unavailable. 9. College-level students are asked at this stage to design adequate modifications to be introduced into the cir- cu it in order to satisfy newly imposed conditions of opera- tion. 10. The posttest in any format (oral, written, perfor— mance, or in a combination of the three testing forms) is to be taken right after the experiment procedure. 11. The modular structure of the model enables it to be used at different levels (i.e., engineering, community col- lege, technical school). The model was applied to the "Electronic Devices Laboratory" course, E.E. 484 (senior level) in the Depart- ment of Electrical Engineering at Michigan State Univer- sity. A total of 108 students were divided into ten lab Sections. Five of these sections (treatment groups) used the suggested model to perform their lab experiment, which happened to be "The Schmitt Trigger-~Theory and Applications." This lab experiment was scheduled to last two weeks, three hours weekly. The other five sections (comparison groups) performed the same experiment in the conventional way of experimenting in the electronics laboratory. The treatment grcamps were monitored by three instructors and the compari— 8011 groups were guided by two different instructors. 125 The following items were prepared to be used in the Schmitt circuit experiment. 1. Theory Sheets——including the Schmitt Trigger's theory and applications. 2. Experimental Procedure Sheets—-including flow charts and special guidance in using the oscilloscope as a display medium. 3. A slide-tape presentation of the Schmitt analysis and applications. These items had been tried out on an instructor and C>r1 a.student before being applied to the treatment groups. The model was evaluated by four tests: pretest, EPCbsttest, retention test (given one month after the posttest), Eirid.student attitude test. An Instructor's Evaluation Form (C>f the model) was filled out by the three treatment group ixlstructors. The results of the four tests were analyzed statis— tJLcally utilizing the CDC 3600 computer at the Michigan State University Computer Center. The Finn Multivariate Analysis CDfE'Variance program was employed in the analysis. Three hypotheses were formulated in the experimental tEisting of the model, two in the cognitive domain and one in the affective domain. It was expected that members of the treatment groups W’Ould achieve higher mean scores on the posttest and reten- tliIDn test than members of the comparison groups. It was also expected that members of the treatment groups would have a 126 Incxre positive attitude toward the specific method of exper- :inuentation they used than members of the comparison groups vvcnald have regarding the traditional approach. The main results of the statistical analysis were a 8 follows : 1. No significant difference (p<0.9544) was found in tJfl£3 mean scores of pretest between the treatment and com— pa rison groups . 2. There was evidence of significance in the mean scores (bf? the posttest (p<0.0004) and retention test (p<0.0001) k>ertween the treatment and comparison groups. 3. No significant difference was found in the mean Sicnores within the comparison groups (p<0.7023) and within tithe treatment groups (p<0.8151) in any of the three tests (EDretest, posttest, and retention test). 4. There was a significant difference (p<0.0120) in the IPC>sitive attitude of the students toward the specific method (Di? experimentation between the members of the treatment ‘gltoups and members of the comparison groups. Conclusions The development of the instructional model for EElectronic circuits laboratory experiments and the perfor- Inanee of the experimental testing led to the following <2 Onclusions : 127 1. By using modern technological means, based on 'trneories of learning, the improvement of learning in the electronic circuits laboratory is possible. 2. Students using the suggested model in experimenta- t:ixon with the Schmitt circuit learned more than those who lassed the traditional method of experimentation. 3. Students using the model retained the material they Lleearned better than students who learned the same material ID}? the traditional method. 4. Students using the model held a significantly more E>c>sitive attitude toward experimentation in the electronics :LEIb than did students using the traditional method of exper- imentation. 5. Learners using the model acquired a feeling of suc— (Zeassful progress in the laboratory experiment (question 7, 'EEige 113). This feeling is considered to be one of the most iInportant factors in motivation. 6. Learning aids are not uniquely advantageous to dif- fferent students. (51 per cent of the treatment groups Inearmbers found the slide-tape presentation helpful, while ‘4E5.l per cent stated that the flow charts describing the eJ'Cperiment procedure had helped in self-proceeding during the l ab experimentation .) Recommendations for Further Research The experimental test of the model carried out in thlis study can be considered as a source of hypotheses for 128 experimental research to be conducted to reach the goal of improving learning in the electronics laboratory. An instructional model for experimenting with electronic cir- cuits (RHUKM: be developed by theory alone, without experi- mental research, and still be valid and helpful in practice. The development of such a model is a continuous process of introducing improvements into the basic prototype and testing their validity. Relationships between various combinations of instruc- tional independent variables and dependent variables might be considered hypotheses to be investigated through experimental research. Some of the instructional variables were dis- cussed at the beginning of this chapter. The model can be extended by conducting appropriate research. Researchers may investigate the extent of reten- tion periods, application to courses at other levels in the engineering college (juniors) and at the community college or technical school level, other laboratory experiments in electronics and electricity, and its application in the realm of techniques of instruction like computer—guided instruc- tion. Each of these investigations would extend the model's external validity. The internal validity of the model might be strength— ened in further research by meeting all the assumptions of the employed statistical analysis. The efficiency of the model as an instructional tool can also be investigated in further experimental studies. 129 Researchers may wish to investigate the use of an integrated lecture—laboratory situation in learning elec- tronic circuits, by incorporating a lecture with laboratory experiences (involving audio-tutorial techniques, programed texts, desk calculators, or computer—aided instruction). Some of the model's features, like the cost effic- iency of Open laboratory procedures, could not be tested, due to restricted circumstances. These, too, might be a worthwhile subject for further research. This model includes a variety of instructional fac— tors like individualized learning, programed experimentation, and self-evaluation facilities (getting natural feedback through the oscilloscope), which provided the statistical results of the study. There were probably some interactions between these various factors. The effect of a certain independent variable might be evaluated by conducting a study in which the treatment groups get the maximum pos- sible variables incorporated in the model, while the com- parison groups perform the laboratory experiment through the same model with the tested variable missing. The writer considers the use of the oscilloscope and the systematic student—oriented procedure for experimentation as the primary means through which student involvement is being increased. BIBLIOGRAPHY 130 BIBLIOGRAPHY Books American Society for Engineering Education. The Application of Technology to Education. Washington, D.C.: Government Printing Office, 1969. Babb, Daniel S. Report of the Electronics Technology Cur- riculum Development Project. Urbana, Illinois: Department of Electrical Engineering, University of Illinois at Urbana-Champaign, 1971. Bandura, A. "Social Learning Through Imitation." Nebraska Symposium on Motivation: 1962. Edited by M. R. Jones. Lincoln: University of Nebraska Press, 1962. . "Vicarious Processes: A Case of No-Trial Learning. Advances in Experimental Social Psychology, II. Edited by L. Berkowitz. New York: Academic, 1965. Bloom, B. S., et a1. Taxonomy of Educational Objectives. New York: David McKay, 1956. Dunsheath, Percy. A History of Electrical Engineering. London: Faber and Faber, 1962. Evans, W. H. Experiments in Electronics. Englewood Cliffs, No Jo: Prentice-Hall, Inc., 19590 Hedges, William D. Testing and Evaluation for the Sciences. Belmont, Calif: Wadsworth Publishing Company, Inc., 1968. Hilgard, Ernst R., and Bower, Gordon H. Theories of Learning. 3rd ed. New York: Appleton—Century- Crofts, 1966. Hook, Sidney. Education for Modern Man—-A New Perspective. New enlarged edition. New York: Alfred A. KnOpf Publishing Co., 1966. Krathwohl, D. R., et a1. Taxonomy of Educational Objec- tives! Affective Domain. New York: David McKay, 1964. 131 132 Mager, R. F. Preparing Instructional Objectives. San Francisco: Fearon, 1962. Markus, John. Sourcebook of Electronic Circuits. New York: McGraw-Hill Book Company. Millman, J., and Taub, H. Pulse, Digital and Switching Waveforms. New York: McGraw-Hill Book Company. Postlethwait, S. N.; Novak, J.; and Murry, H. 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APPENDICES 135 APPENDIX A THEORY SHEETS 136 137 Michigan State University Department of Electrical Engineering and Systems Science Electronic Devices Laboratory I BB 484 -- Fall 1972 THE SCHMITT TRIGGER -- THEORY AND APPLICATIONS Shlomo Waks THEORY SHEETS 1972 138 Michigan State University Department of Electrical Engineering and Systems Science Purpose THE SCHMITT TRIGGER-~THEORY AND APPLICATIONS To improve the understanding of the student in the operation and application of the Schmitt Trigger and increase his laboratory skills. Objectives Given a diagram of the Schmitt Trigger, you will be able to do the following after completing the experiment. 1. Explain (orally or written) the Operation of the Schmitt Trigger and the role of every single com— ponent in the circuit. Point out the expected waveshapes of the voltages at the various points of the circuit in the stable and triggered states. Predict possible changes in the operation of the cir- cuit as a result of a great change (over 70%) in one of its component values or sources. Predictions like: "the output transistor 02 will not change its satura- tion state" are acceptable. Point out possible reasons for differences between calculated and measured voltages at various points in the circuit. Suggest necessary modifications to be carried out in order to adapt it to new operating conditions with 139 different supply or driving voltages, change in loading or in environmental conditions. Applications of the Schmitt Trigger To automatically control street lighting or neon sign switching an automatic twilight switch is required to switch the artificial lighting on or off, depending upon the inten- sity of the daylight. The following block diagram shows the basic components of such an automatic twilight switch (Figure Al). Artificial Street Lights L.D.R. Ambient i Light Q: POWER \ '\/ \§:> '—*~ :><: "-*~ REHLAY’ —a— SWHITHH F*:::j--' / 1 I Figure A1.—-Block diagram of a twilight switch. In the evening when ambient light intensity drOps, the resis- tance of the Light Dependence Resistor (L.D.R.) increases. When this occurs, the artificial street lights have to be turned on automatically by the power switch which is Operated by the relay. The relay is activated by a definite supply of current through its coil. Since the L.D.R. changes its resistance gradually (as a result of gradual change in ambi- ent light) there is need for a device x (see Figure Al) which 140 will transfer slow changes in the voltage across the L.D.R. into fast changes of voltage (or current) in order to acti- vate the relay at a definite ambient light level. The Schmitt Trigger circuit can fulfill the above requirements for the device x. Let's analyze this circuit and see how we can utilize it for various applications. The Schmitt Trigger is an electronic circuit which gives an accurately shaped, constant-amplitude—rectangular pulse output for any input pulse above a predetermined trig- gering level. This circuit can be used as a d-c signal-level detector or an amplitude comparator, to produce an abrupt change in voltage when an arbitrary waveform reaches a par- ticular reference level. Squaring of arbitrary input signals is one of the fre- quent uses of the Schmitt Trigger, as Figure A2 illustrates. Some of the applications of the Schmitt Trigger circuit are in: 1. Radiation counters, 2. Opto-electronic aparatus such as optical counters, 3. Liquid-level sensor, 4. Automatic lighting controls, and 5. Square wave generators, to "square off" a sinusoidal input. In the above-mentioned applications, as well as in other cases, the Schmitt circuit uses as a "trigger" circuit which translates the slow-changing voltage accepted for 141 instance from a transducer (photo sensitive device, radia- tion counting tube, etc.) into triggering signals which acti- vate the relay or electronic counter. +0-——— --——-.+ v Schmitt ' v i Trigger o 0—1 --———-0 ! 01 T l I 1:0 -— _ - q— — Figure A2.-—Input (vi) and output (v0) waveshapes of a Schmitt Trigger. Let us now see how the Schmitt circuit functions and find the key factors affecting its Operation. Analysis of a Schmitt Trigger Circuit The basic Schmitt Trigger circuit consists of two inverting amplifier stages, Al and A2, connected to deliver positive feedback as shown in Figure1¥3o The feedback is positive only when regarding the closed loop B2, E2, E1’ 142 Figure A3.--Basic circuit of the Schmitt Trigger. Any type of inverter may be used as active component in the amplifier stages A1,.A2,such as vacuum tubes, bipolar transistors, field effect transistors, or integrated circuit operational amplifiers. Quantitative Analysis of the Transistorized Schmitt Trigger Circuit Figure A4 shows a transistorized Schmitt trigger cir— cuit. Let's see what happens in the circuit when vi starts raising from Ov. When vi = Ov, transistor Ql is forced into the cut-off state because its base-emitter junction is reversed biased by the voltage drop on RE' Transistor 02 is in conduction because it is biased adequately via RC , 1 R1 and R2. Neglecting the leakage currents of the transistor in cut-off (Ql), the circuit may be described as in Figurelfihl. After applying Thevenin's theorem at point B2 (looking to 143 Figure A5.--Equiva1ent circuits of the Schmitt Trigger when Ql is in cut-off and Q2 is in conduction. 144 the left) we get the circuit depicted in Figure A5b- Here: . R (R + R ) V' = Vcc :2 ; R = 2 1 Cl (1) RC1 + R1 R2 B R1 + R2 + RCl In order to calculate the voltages and currents in the circuit, let's remember that the input characteristics of a transistor might be described approximately as in FigureZUS. For our analysis, let's consider the more general case where the transistors are not necessarily driven into saturation. 181 l :VBE . ' 4V 0 vA ‘ BE Figure A6.--Input characteristics of a transistor. The operating currents and voltages can be calculated from the equivalent circuit shown in Figure A5b. According to Kirchhoff's voltage law applied to the base emitter circuit of 02: ' _ .— — = v IBZRB VBE2 IB2(hFE + DRE 0 (2) 145 V' - V 2 RB + (hFE + 1)RE As long as Ql stays in the cut-off state, the output voltage will be: _ (0) _ _ 1 ‘ Vo " Vcc hFEIBZRCZ (4) V Increasing the input voltage vi will cause Ql to start con- ducting. If we define VT as the input voltage which causes 1 Q1 to start conducting, then: v. = V = V + V = I (h + l)R + V 1 T1 E yl B2 FE E Y1 = (v' _ v ) (hFE + 1)RE + vY BE2 RB + (hFE + 1)RE 1 (5) ' .. V VBE2 vTl = R + vyl (6) l + B (hFE + 1)RE Consider the closed lOOp B2, E2, E1’ C1’ B2 in FigureZHS. The loop gain of the Schmitt in Figure A4 is the overall voltage gain of the whole loop. In our case, for instance, when a signal of Av is delivered to base B2, this signal is transferred through Q2 and appears at E2 uninverted (in the same phase as at B2), now it is delivered through E1 to transistor Ql that Operates as a common base amplifier (because the input signal is delivered to the emitter while the base B can be considered grounded). From collector Cl 1 the amplified (and noninverted) signal is transferred back 146 to base B2 via a voltage attenuator involving R R and 1' 2’ RC . If the loop gain in this circuit is less than unity, l the circuit will Operate for vi > VT as a simple direct l coupled two stage amplifier with positive feedback. The increase in the input voltage vi causes a decrease in col- lector voltage of Q1 which in turn lowers the voltage sup- plied to the base of Q2, thus causing an increase in the output voltage v0. Further increase in vi lowers the base voltage of Q2 till finally O2 is driven into cut-off. Addi- tional increase in vi does not effect the output voltage which is now at a constant value v0 = Vél) = V CC' The transfer characteristic v0 = f(vi) of the circuit is shown in Figure A7. The slope g;% of the transfer function in Figure A7arepresents the overill voltage gain of the circuit. Increasing the loop gain by raising the value of RC1, for instance, will cause a steeper slope. When the loop gain is unity, the lepe will be infinite, and the circuit will begin to regenerate. No more linear amplifi- cation will be available. Further increase in 100p gain results in a nega- tive slope and the transfer function assumes the hysteresis shown in Figure A8. Since the Schmitt circuit is mostly used as a fast regenerative triggering device, loop gain greater than unity is established; therefore, the transfer function in Figure A8 usually appears in application notes, data sheets, and chapters in books dealing with the Schmitt Trigger. 147 o A v o l 02 Q Q - 1' 2 in cut off (a) V(l )-—- incond. V(1)-< o 1AM» o ._A$_._.___- .1 _. o v.0 w: ‘ % $v 3" VTl VT2 1 q t o (C) ----- v. o ’ 1 KC ("M ‘ V- (b) “‘4E:w-~ 11 v. 1 ,1 Figure A7. (a) Transfer function of the Schmitt Trigger when (loOp gain) < l. (b) Input sinusoidal voltage. (c) Output voltage waveshapes, vo--operating in the linear region, v$--output voltage clamped. veil V(1)-q- ——--‘-~-——-———--- 0 I) V(0)‘ o n : =V- o V% VT 1 2 1 Figure A8.--Transfer function of the Schmitt Trigger for (loop gain) > 1. 148 To Conclude: Raising vi from zero volts will initially hold the Schmitt Trigger in its "low" stable state: v0 = véo) = VCC — IB2(hFE + l)RC2 (Ql off, 02 conducting). When vi reaches the value VT (Eq. 6) the circuit switches over rap- 1 idly to the "high" stable state, where v0 = vél) = VCC (Ql conducting, 02 off). Further increase in vi will have no effect on the output voltage v0. Now, when decreasing Vi' the circuit won't (0) 0 starting from values higher than VT , 1 switch back to the low stable state v as vi reaches the value V . The reverse transfer of the circuit from the T 1 high stable state vél) 60) to the low state v will happen at v. = V < V . 1 T2 T1 The difference (VH) between the two triggering voltages VT and VT is known as the hysteresis voltage of l 2 the Schmitt Trigger: V = V - V (7) H T1 T2 We will prove the existence of the hysteresis voltage by develOping equations for VT and VT , and then investigate l 2 the factors affecting this voltage. We have already developed an equation for VT ; the 1 result was (Eq. 6): “7:7— “‘7'. . T .1..'_ 149 Refer to the Schmitt circuit in Figure A6, where v R R2(R1 + Rc ) R1+R2+RC b Rl+R2+RC 1 1 V -- cut in voltage of Q Y1 l The effect of the resistor RE on VT is easily seen in Eq. 6; 1 when RE is increased VT decreases. 1 In many cases, RB << (hFE + l)RE, so then Eq. 6 can be written in the following form: v g v' - v + v (8) T1 ‘ 332 Y1 Usually, in silicon or germanium transistors - V = 0.1V, SO VBE v R v R 60 CC 2 I» CC 2 V _ (V' - 0.1)v = - 0.1V = Tl — R1 + R2 +RC R1 + R2 + RC (9) 1 1 T1 E It is possible to design the Schmitt Trigger so that In this case, V is independent of hF the transistor 02 (FigureZVU will be in saturation (when Ql is in cut-off) instead of being in the active region. In this case switching time will increase. Calculation of V T2 VT is the input voltage which causes the reverse 2 transition of the Schmitt Trigger from the high state ("1") back to the low state ("0"), by cutting off Q1 and driving 02 into conduction. 150 Referring to the transistorized Schmitt circuit in FigureZML Ql is now conducting (active region) and 02 is in cut-off. v is being decreased. We want to calculate the- H. voltage vi = VT which will cut Off 01' The equivalent 2 circuit of the "high" state of the Schmitt Trigger is shown in Figure A9. Figure A9. Equivalent circuit of the Schmitt Trigger when Ql is on and Q2 is cut off. Figure Au)shows the Thevenin equivalent circuit of the collector Cl and base b2 circuits. V" is a Thevenin voltage source: v" = v R1 + R2 (10) cc R1 + R2 + RCl 151 with an internal resistance R (R + R ) C1 1 2 (11) R1+R2+RC R: 1 Note: Meanwhile ignore Re assume points El - E being shorted. ‘ I“ .-._v:.r.‘——' R!‘ Figure A10.--Thevenin equivalent representation of collector Cl and base b2 portion (Ql on, 02 off). Applying Kirchhoff's voltage law to the base emitter circuit of Q2 just before it begins to conduct, we get: R 2 V - V - I (h + l) = 0 (12) Cl R1 + R2 Y2 81 RE FE R2 (V" - h I R)—--——— - V - I (h + 1) = 0 (13) FE Bl R1 + R2 Y2 81 FE IT 152 R (R Vedwaz _ h I C1 1 (R1 + R2 RC1).(.RI—+—R37 FE Bl (RCl + R1 + R2) (R1 + R2) + R2)R2 - VY2 - IBlRE(hFE + 1) = 0 (14) I = (15) H O M New, writing Kirchhoff's voltage law for the base- emitter circuit of Q1 we get: v. = V = I R + v + (h + 1)I R (16) 1 T2 Bl S BEl FE Bl E ' .. (V VY2)[RS + (hFE + 1)RE] V = v + (17) T2 BEl RCl R2 h + (h + 1) FE RC + R1 + R2 RE FE In many practical circuits R << (hFE+l)RE and h S FE << 1, then the input voltage VT which causes the reverse transi- 2 tion of the Schmitt Trigger (from "1" to "0" state) is: 2 E (18) If the above assumptions are met, VT is independent of the 2 source impedance R and hFE' S 153 Sometimes, a further approximation is made, namely, VBE ; 0 ; VY ; 0 , in this case: 1 2 V R V. 2 R R CC 2 <19) 2 Cl 2 +R +R +R RE Cl 1 2 The Hysteresis and Its Elimination Equation (7) defines the hysteresis voltage VH of the Schmitt Trigger circuit; substituting the approximate values of VT (Eq. 9) and VT (Eq. 19) we get: l 2 V = V _ V VCCRZ vCCRZ H T1 T2 R1 + R2 + RCl RCl R2 R + R1 + R2 + RC 1 2 v R R v = cc 2 cl (20) H R R Cl 2 RE[Rl + R2 + RC1] -—§E——-+ R1 + R2 + RCl In cases where the hysteresis is undesirable it might be eliminated by adjusting the loop gain to be unity (then VT = VT ). There are several ways to adjust the lOOp gain: 1 2 1. Increasing the gain by increasing RC (See Figure All). 1 2. Decreasing the gain by adding a resistor R8 in series with the emitter E (See Figure)!” . This resistor 1 will increase VT because of its own voltage drop: 2 (hFE+l)IB Re' If necessary, Re may cancel the entire 1 voltage. If IB (Figure A9)remains unchanged, then: 1 H T T B e FE + l) (21) The value of Re required to cnacel the hysteresis voltage VH will be: VH R = 22 e (hFE +1)IBl ( > where IB is determined by Eq. (15). 1 Re affects only VT (when Ql is conducting) and does 2 not affect VT at all. (Why?) 1 3. The gain may be adjusted also by varying the ratio R2 §I_:_§; , Figure 4. Decreasing R2 or increasing R decreases the loop gain. To maintain a lOOp gain 1 value of precisely unity, frequent readjustment is necessary. However, loop gain less than unity results in loss of speed in the response of the cir- cuit. As a trade-off then, a slight hysteresis is tolerated in many practical cases. The time elapsed from the moment that vi hits VT 1 (or VT ) to the moment that the output has "settled" at its 2 new level is called the switching time. Switching time is sometimes decreased by shunting R with a Speed-up capacitor C 1 (See Figure A4) . This capacitor easily transfers the voltage transients from the collector of Q1 to the base of 02’ thus avoiding their attenuation by resistor R Detailed computa- 10 tion of the Schmitt circuit Operation is presented in the next example. This example is also an outline of the experi- ment to follow. 155 Example: Given the Schmitt Trigger circuit in Figure.All. V CC Figure All.--Calcu1ating example of the Schmitt Trigger. VCC = 12v C = lOOpF R = 4K9 C1 R1 = ZKQ R2 = 6K9 RE = 3K9 RS = lKQ 01:02 silicon transistors with hFF = 30. V = 0.6V. V = 0.5v. BE Y 156 Calculate the following: 1. 2. Base current of 02' RC , when S is Open. The output swing voltage has 2 to be 4 volts. Loading Effect: After connecting the load RL = 5K9 by closing the i switch 8, to what value must RC2 be changed in order g to maintain the output voltage swing unchanged? 3 Calculate V283 and Vég; when S is closed. E Triggering Level: Calculate VTl and VTZ. Hysteresis: Calculate the hysteresis voltage VH' Effect of D.C. Voltage Supply, VCC: Repeat steps (1), (2), (5) and (6) with VCC = 6v. Effect of Triggering Source (vi): Which of the calculated values, V , V is affected T1 T2 by the internal resistance RS of the triggering source vi? Why? Calculate this value when RS = 5K0 (and VCC = 12v). Compare to your result for RS = 1K0. Effect of Circuit Components: Repeat steps (1): (2)! (5) and (6) With RE = 5000(VCC = 12v). Is now the Schmitt circuit Opera- tion more dependent on the hFE of the transistor than in the case when RE = 3K0? 10. 11. 157 cl' R1' R2 and C on the loOp gain and hysteresis of the Schmitt Explain in your own words the effect of R circuit in Figure 11. Hysteresis Elimination: Calculate the value of a resistor Re connected in series with El’ required to eliminate hysteresis. Note: You will benefit very much if you try to solve the above example, step by step, before looking at the solution. Solution 1. Base current calculation: (IB ) 2 BY Eq- (1), . = 12 ° 6 _ _ 7(4 + 2) = 3K V 4 + 2 + 6" 6V RB - 4 + 2 + 6 Substituting into Eq. (3), _ 6 - 0.6 _ 5.4 _ I82 ‘ 3 + (30 + 1)3 ‘ 9 ‘ 0'056 ma 2. Calculation of RC : (S open) 2 In the "1" state: - (l) _ _ vO — VO — VCC — 12v. The output swing voltage is: (l) _ (0) _ V0 V0 — 4v. By eq. (4), (0) = _ _ (l) _ = _ e VO VCC hFEIBzRC2 — VO 4 12 4 8V. R = YEE_:_? e 12 ’ 8 = _i_—.= 2 38K C2 hFEIB 30 - 0.056 1.68 158 3. Loading Effect: (8 closed) Thevenin's equivalent circuit at the collector of Q2 when S is closed is shown in Figure A12b. The swing voltage Vél) - V30) is actually the voltage drop across the equivalent collector resistance R'. Since the base cur- rent IB does not depend on the collector resistance, I remains as before, and R' = R = 2.38K. 32 C2 CC RI C2 C2 IB 2->- Q 2 RE -£= - 7: (a) (b) Figure A12.--(a) Output circuit of the Schmitt, loaded by RL; (b) Thevenin's equivalent circuit of (a). The required collector resistor Ré will be: 2 I Rc RL R R' _ 2'38 = 4.54K 2.38 w H w I I o 70 | WW I 3 a; 45.2“. .___, 159 The "1" state output level of the Schmitt when S is closed is: R V41) = Vcc = Vcc R' E R = 120.52: + 5 = 10'9V° C2 L. The "0" state output voltage will be: V30) = 10.9 - 4 = 5.9V. Triggering_Level. By Eq. 6: vT = 6 ‘ 036 + 0.5 = 5.2 + 0.5 = 5.7V. 1 1+§i—.—'7 Using the approximate formala for VT , Eq. (9), assuming: 1 R (h + 1) >> RB: v 2 v' - 0.1 = 6 - 0.1 = 5.9V. Here: R (hFE + l) 3.31 = 93K >> R.B = 3K. So, a relative error of RB x 100% = 3.2% caused RE(hFE + 1) a close error in VT of 1 5.9 - 5.7 5.9 x 100 = 3.4%. By Eq. (17): (6 - 0.5)(1 + 31 ° 3) 4.6 4 + 2 + 6 + 3'31 V = 0.6 + = 0.6 + 3.4 = 4.0V. T1 30 Applying the approximate formula for VT , Eq. (19), when 1 assuming: (h BE 2 0 and VY g 0: we get for VT : 1 2 FE 160 12.6 T 34.6 2 —§—-+ 4 + 2 + 6 V = 3.6V. Hysteresis. The hysteresis voltage VH’ Eq. (7), is: V = 507 — 4.0 = 1.7V. H Effect of a D.C. voltage supply, VCC' Base current calculation: IB 2 6.6 6(r + 2) '— - = = V 4 + 2 + 6 3v. RE 4 + 2 + 6 3K9 _ 3 - 0.6 _ 2.4 _ 182 3 + (30 + 17" 9 ‘ O 025 ma“ Output voltage swing: calculation of RC 2 (l) __ (0) _ . (1) __ _ (0) __ (l) __ _ V0 V0 - 4v, VO — VCC - 6v. VO - VO 4 — 2v. R = 4 = 5 34K C2 30 - 0.025 ’ ' Applying Eq. (6): v = 3 ' 0'6 + 0.5 = 2.32 + 0.5 = 2.82v. T1 1 + ———1—— 31 . 3 Or approximately by Eq. (9): V '33 -001: 209V. T _ 2 Using Eq. (17): V = 0.6 + (3 - 0.5)(1 + 31.3) = 0.6 + 2.5 ° 94 = 2.14v. T2 30 4'6 + 3-31 153 4 + 2 + 6 The approximate value of VT , using Eq. (19), is: 2 161 6 - 6 + 4 + 2 + 6 <2 llc> = 1.8v. 2 4.6 3 The hysteresis voltage is: VH = 2.82 - 2.14 = 0.68V. Effect of Triggering Source (Vi)' S' because this triggering voltage is determined when O1 is in cut-off (no current flows VTl is not affected by R through R I = 0). When calculating VT , Ql is con- 5' B1 1 ' ducting (see Figure.A9)and the voltage drop across RS has to be taken into account when calculating VT2 [see Eq. (16)]. With R8 = 5K0, VT will be, according to 2 Eq. (17): v = 0.6 + (6 - 0.5)(5 + 31 . 3) T 4 . 6 2 304+2+6+3°31 = 0.6 + 3.52 = 4.12V. VT raised by 0.12v when replacing RS = 1K0 by RS = 5K0. 2 Effect of Circuit Components RE = 5009 = 0.5K Substituting into Eq. (3), the base current in Q2 is: _ 6 - 0.6 _, 5.4 _ I82 ‘ 3 + (30 + 1) - 0.5 ‘ 18.5 ‘ 0'29 ma‘ Applying Eq. (4), the collector resistance of Q2 is: _ 4 _ RC2 - 30 , 0.29 — 0.46KQ. The triggering voltage VT [Eq. (6)] 1 10. 162 + O In H 4.5 + 0.5 = 5v. )1+31-0.5) + 0.5 - 31 v =0.6+(6"0' T2 30 4 4+ = 0.6 + 1.2 = 1.8V. 5 ( - 6 2 + 6 The hysteresis voltage is: V = V - V = 5 - 1.8 = 3.2V. H T1 T2 Now, with RE = 0.5K the operation of the Schmitt Trigger circuit is more dependent on the hFE of the transistor than in the case where RE = 3K because the assumptions FE 1 1)RE >> RB and (hFE + 1)RE >> RS are more va11d when RE is higher. Only after accepting these assumptions with the “rm““fi. (h approximate equations for V and VT [Eq. (9) and 1 2 Eq. (19)] show independence in hFE‘ T Referring to the Schmitt Trigger circuit shown in Fig- ure.All,R is part of the collector load resistance of C l the first amplified stage Ql‘ Hence, lowering RC will 1 decrease the amplification, thus decreasing the loop gain. As a result the hysteresis voltage VH will become smaller. R1 and R2 are connected as an attenuator while transfer- ring the signal from the collector of Q1 to the base of R2 +R. Qz. It is a simple voltage divider with a ratio 1 2 R This voltage divider is part of the closed loop B2 B2 E El C1 B2, so when R increases or R2 decreases 1 there is more attenuation, causing a decrease in loop gain and in hysteresis voltage VH‘ 11. 163 Connecting a speed up capacitor C in parallel with R1 is like lowering Rl during the transition period (which is of A.C. character). Thus, loOp gain is increased when transitions occur. The hysteresis voltage VH VT — VT is determined by the two stable D.C. conditions 1 2 of the Schmitt; therefore, the capacitor won't affect the hysteresis voltage VH' Too large a capacitance of C might require an excessively long discharge time, thus lowering the maximum frequency of operation of the circuit. Hysteresis Elimination From Eq. (15): 5 = EL; = 0.036 ma. + 3(31) H H 00 II +J>~ox 0. 6 + 6 NOI 1 3O 4 Hysteresis might be eliminated by inserting a resistor Re in series with emitter El' If we want the current IB 1 to remain unchanged with Re connected VT has to be 2 increased by the amount of the voltage dr0p across Re' Since we want to eliminate the hysteresis voltage V = V - V we will choose such a resistor R that H T1 T2 e w111 cause an increase in VT2 so that VT2 = VTl. (VH will then be zero.) Therefore, according to Eq. (22): V. _ H _ 5.7 - 4 _ 1.7 _ Re ‘ IB (hFE + 17*‘ 0.036 - 31 ‘ 0.036 - 31 ‘ l'SK“ 1 164 Various Types of Schmitt Trigger Circuits and Applications 1. PET Increases Schmitt Input Impedance. - - - 10V 10K Ql V0 2 N2608 0. .OluF - 2N404 II + (.|———' -9v 0K 500K V T o g... h .— - Figure Al3.--High impedance Schmitt. Use of a PET for input stage gives high input impedance, as required, for some threshold detector circuits. Out- put pulse is square wave at up to 100 Kc triggering rate. Turn-off threshold is about 0.2V. below turn-on. L. R. Lott, Electronics, 38:15, p. 65. 2. Diode and Resistor Increase Input Resistance of Schmitt Addition of Rb and D1 reduces loading on driving cir- cuit when Ql is on, thereby preventing input signal from being clamped. Same signal may therefore drive other Schmitt Triggers having higher trigger levels. (Figure A14) J. Gaon, Electronics, 39:12, p. 110. ,. 165 2N2270 Figure A14.--Diode modified Schmitt. 3. An Integrated Circuit Operational Amplified Schmitt Trigger V V A = _° )0 v2 v1 (1) = +5v v = ,— O V 1 v0 1 v o V V T2“ T1 v(0)=-5vd 1 (b) (a) v T Figure A15.--(a) Op-amp Schmitt. (b) Input-output transfer function. 166 Since the operational amplifier has at least two amplify- ing stages (two inverters), a positive feedback loop may be established easily. Such a feedback arrangement is shown in Figure A15(a). When using appropriate component values, a Schmitt Trigger Operation is established as depicted in Figure A15(b). Let's analyze an Op-amp Schmitt incorporating a typi- cal Operational amplifier with the following character- istics: A 2 5000 Z. > 20K in Z < 25 0 Output Swing = i5v peak; i.e., Vél)= 5v. V30): -5v. Referring to Figure.AEMa), R1 and R2 are chosen in R R such a manner that R >> Z and —L—;——— << Z. . Voltage 1 0 R1 + R2 in VT is supplied externally-—it sets the (threshold) trigger level of the Schmitt. Feedback loop gain 2 A ——————— (23) R1 + R2 If this loop gain is greater than unity the output is forced into saturation at either +5v or -5v. The (positive) feedback voltage Vfb is: R V R + V R 2 T 1 o 2 V = V + (V - V ) ——————— = (24) fb T O T R1 + R2 R1 + R2 In the "1" state of the Schmitt, v0 = Vél), so: 167 T l 0 2 V = (25) fbl R1 + R2 _ (1) and (Vfbl Vin)A 2 V0 (26) When Vin = VTl then the triggering voltage VTl is obtained: (1) (V - V )A = V fbl T1 0 __ (1) A vfbl vO v31) m V = = V - = V (27) T1 A fbl A fbl Similarly, in the "0" state, v0 = V30), (0) Vfb = VTRR ++VR R2 (28) 2 1 2 The triggering voltage VT (which transfers the Schmitt 2 from the "0" to the "1" state when vi decreases) is: (0) V0 llc’ v = v - v (29) 2 sz A sz The hysteresis voltage VH by decreasing the loOp gain by lowering R2. If the loop = VTl - VT2 may be decreased gain is then unity the circuit will Operate as a dif- ferential amplifier with a linear region, as in a dis— crete transistorized Schmitt. Using the above-mentioned typical operational amplifier in a Schmitt circuit depicted in Figure A15(a), with: R = lOKQ, R = 509, V 1 2 = 2v the folloW1ng Th 168 Operation results are obtained: Feedback Loop Gain = 25 > 1. Vfb ; 2.025 v ; Vfb ; 1.975 v. 1 2 VT = 2.024 v ; VT = 1.976 v. VH = 48 mV. 1 2 Preliminany The circuit under experiment is given in Figure A16. v 01' 02 ' hFEzSO Icc = O V - ‘ VY 0 5 3.3K RC c(150 pF) R VB - 0.6V 1 c 2 R C21r———'—-. “I R B l + Q ° 02 1K - v 2 o < .+ {11 H E1 m (D m 1| u U) 7: F3 N Figure A16.-—The Schmitt Trigger circuit under experiment. In the "high" state of the Schmitt the required output ‘voltage level is 12 v. Leakage currents of the transistors xnay be neglected. 169 Calculate the following (and write down the results in the Experiment Procedure sheets): 1. Supply voltage VCC' 2. RC2 (when RL is disconnected) to get an output swing voltage of 3 volts. 3. Given vi = 0v, calculate the voltages at the following points in Figure A16: 31' E132, C2. Write down the results in Table.Blin.the experiment sheet. 4. Calculate the triggering voltages VTl, VT2 and the hysteresis voltage VH. 5. Draw down the output voltage shape of the Schmitt if the input voltage is a half sinusoide as shown in Figure A17. v , (1° 17° (1) 1 y_ v(l)__ __ _ __ V0 -h- V 7‘ —— —°.- V A (0) _ - V30) #—.—~| — --— V0 '1' —' 4 J.,—V fit 1 v 1; T2 [Tl l t I = 1 ----- . v. T) 1 t2 -r’ I l .1. t3 “‘4‘ -39 t4 - Figure A17.—-Determining the output waveshape of the Schmitt. 170 6. Repeat steps (3) and (4) when RL = 1K0 is connected at the output (Figure.Al6). What is now the swing voltage? Vcc ' = —— 7. Replace VCC by VCC 2 . Repeat steps (2), (3) and (4). (RL disconnected). 8. Assuming VCC as calculated in step (1) and RL dis- connected (See Figure A16),calculate VT2 when the value of R8 13 SK. 9. Calculate Re to be connected in series with the emitter of O1 in order to eliminate hysteresis. 10. Assume that the transfer characteristics of the Schmitt circuit are as shown in Figure A18. v If V , V values as calculated T T V(l)-o—- ———-- -—~—‘—- 1 2 o l H in step (4). V0 l l ' I i . 0 V V 7:: V1 T2 T1 JFigure 18.--The transfer characteristics of the Schmitt Trigger. Sketch the transfer characteristics and output wave- shape in each of the following cases, when (Input volt- age vi is the same as in Figure Al7)only one component value is changed at a time, while the others remain in their nominal values as in Figure A16. ‘m magnum-mtg." .J ._4 171 a. R increased (R' 2R ) C2 C2 C2 I _ b. RC decreased (RC — 0.5Rc) 1 l ' = c. Rl decreased (Rl 0.5Rl) l _ d. R2 decreased (R2 — 0.5R2) e. RE decreased (RE = 0.5RE). What happens in every case with: VT , VT , VH' V30) and 1 2 V51)? Do we have in all the cases a bi-stable Operation of the Schmitt or does the circuit Operate also as an amplifier within a certain linear region? Give des- criptive answers (numerical values unnecessary). Selected References Pulse, Digital and Switching Waveforms by J. Millman, H. Taub McGraw-Hill Book Company Digital Electronics With Engineering Applications by T. P. Sifferlen, V. Vartanian Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1970 APPENDIX B EXPERIMENT PROCEDURE 172 173 Michigan State University Department of Electrical Engineering and System Science E.E. 484 — Fall 1972 Schlomo Waks © 1972 The Schmitt Trigger — Experiment Procedure The procedure of the experiment is laid out in a flow chart depicted in Figure Bl. It may be very helpful to pro- ceed step by step according to this flow diagram while referring to the attached tables and briefings pointed out by the number in parentheses fixed at the lower right corner of some blocks in Figure Bl. Introduction and "Stable-State-Operation" Experimenting Procedure Refer to Figure B1. (1) [Enter] Given the practical Schmitt circuit (shown in Figure BZ) mounted on a board, 2 D.C. power supplies (Trygon Electronics, Mod. HR40v.-750ma), one audio gen- erator (hp Mod.200 CD), one oscilloscope (hp. Model 130A), VTVM (hp. Model 410B). This equipment is assembled on your working bench in the electronic laboratory. (2) A.slide-tape presentation of the Schmitt Trigger (analy- sis and applications) will help you to understand the «Operation and possible applications of the Schmitt cir— cniit. You may use the slide projector and tape explana- ‘tions not only in this stage (before you start the eaxperiment), but also later during the various steps of exp er iment ing . ywe “aw...— ' .. __,_ mesa _w. 6x63 oeoenm .musomuoum mcaucmswummxu =coflumuwmo musumumanuum= one coauUDUOMucHun._M 0.53m mamsemce .o.< ou 1|]-II'I'I‘II'I'-‘III"I'II.I'III|.IIIl|lllll1lllllull|lll' 174 \» _ Anne BHZD UZHBOO:m mamDOmB is. 1 _ muCOEOQEOU ;, _ mucwESAumcH mcoHuowccoo monocoeeou m>flmmsm m _ a mommuao> Ufisonuo x0020 o>euo< umme ousmmmz coHuaocoo _ xammsm xomru a xuozu maneum oouowmxm _ now 02 _ fl , uOu we» lusuumcH “ Hutu _ oz 4 oz 32 _ meAs> manmum _ ucoemflseu muomucou newcomeoo unecomEOU Uwuoomxu _ manoeuvmo nucmvm mosammm Tosasmm Ou mnmeeoo _ he confines _ . L I ~ 1 _.l Ame Ave ”my Ammo Ame :oHnsummo Amxueuonm . N . 70.3 ixoocov muouoz pouosuumcH rue: own ou> {1 Meoszuasz wumum 383w a Nu¢ .3) .ESOud mo J concurs ousmmoz ecmccct muasmmm xooro oumHsuHmo noun: a cmuqu Heme xomEmm a mac: m.uOu losuumcH new 175 Figure B2 shows the diagram of the circuit under experiment. 01,02: hFE=50. V =0.5v. Y — VBE-O 0 6V 0 silicon Figure B2.--The practical Schmitt Trigger under experiment. (3) If you have already calculated V and RC in your pre- CC liminary work, use those results. Check these values with the instructor before connecting RC2 and VCC to the circuit. Present your whole prelim. to the instructor. (4) Carry out the following measurements (RL not connected yet). (a) The expected voltage values are those you have already calculated in your preliminary work--write them down in the "calculated" portion of Table Bl. 176 Table Bl. Stable State ("Low") Voltages in the Schmitt Trigger. Vi = 0v. Calculated (V)c Measured (Vimt __!)c-(th VBl (v) VE (V) V132 (V) VC2 (V) (b) Start increasing the input voltage and fill out Table B2. Table B2. Transferring the stable state of the Schmitt. Vi(V) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Vo(v) Note where VO has changed, measure the precise value of V1 that causes transition: V = T1 (c) Measure VT - the input voltage that brings back the 2 Schmitt to its original state ("low"). VT = 2 (d) Make comparison according to Table B3. Table B3. Comparison between calculated and measured triggering voltages. Calculated (VT)c Measured (VT)M (VT)c-(VT)M V (v) v (V) (e) Determine the hysteresis voltage V 177 H. (Table B4). Table B4- Calculated and measured hysteresis voltage. Calculated (VH)c Measured (VH)M (VH)c-(VH)M "A.C. Nominal Operation" Procedure After completing the D.C. measurements described in Figure B1, proceed from step 2 according to the procedure laid out in Figure B3. Now you will investigate the A.C. nominal operation of the Schmitt circuit. Note: Don't forget to connect D1 and R = 3.3K as shown in Figure B4. Supply Measure Compare to Yes Get the A.C. input & expected the expected transf. input. 11 output waveforms waveforms charact. voltage waveforms (6) ? on the (5) (6) scepe (8) :1 = charact . Call Instr. on screen Ffixnrre B3.--"A.C. Nominal Operation" experimentation procedure. 178 (5) Deliver a sinusoidal input voltage from the audio gener- ator through a "half wave rectifying" arrangement as described in Figure B4. 1N503 J R B VP ’ [>% ‘ é —JV$WVV g- Figure B4.—-Triggering the Schmitt with half a sinusoidal voltage. (6) Connect the output voltage VO (Figure 32) to the vertical input of the oscilloSCOpe. Make necessary alignments of the scepe to get the output waveshape on the screen. Draw the required output shapes in Figure BS. Expected output waveshape Measured output waveshape (1 VO (v) VOW) —v- t 0 r t 0 (a) (b) Figure BS.--Expected (a) versus measured (b) output waveshapes. 179 (7) If you didn't get the expected output waveforms start following the "Trouble Shooting Unit," as described in Figure Bl, but first check the ngw_connected contacts and components (Vi, D1, R in Figure B4). (8) Getting the Transfer Characteristics of the Schmitt Circuit on the Oscilloscope. Leave the same input- voltage arrangement as shown in Figure B4 and connect the input and output terminals of the circuit to the oscilloscope as depicted in Figure B6. to horiz. input “vs 1 Ex [Lt D 1 6V“ N W—a— _+.. to vert . + M R V input 3 . " t 6V5 3 . 3K Schmitt o Trigger lKH ‘ —_1_- ' Figure B6.--Getting the transfer characteristics on the oscilloscope. Notes (a) Don't forget to disconnect the internal sweep of the oscilloscope by turning the "Horiz. Sensitivty" knob to some horizontal sensitivity value (say 1 volt/cm.). (b) In order to get the true voltage values (including the D.C. component), set the "input" knobs (switches) to D.C. position. 180 Make necessary alignments of the scope to get the transfer characteristics on the screen. Draw the expected (dashed line) and measured (solid line) transfer characteristics in Figure B7. VO (V) 0 Nominal Transfer Characteristics = Vi (V) Figure B7.--Expected (dashed line) and measured (solid line) transfer characteristics of the Schmitt. Hysteresis Elimination. Proceed according to flow chart shown in Figure BB. Insert Re in series with El (Fig. 32) (9) Get transfer Compare Change characterist. to ex- value on sc0pe pected of Re transf. (ll) charact. (10) { Observe Check con- change in tacts and __ transfer computation ‘— character. of Re. and output waveshape (ll) l8]. (9) Use the value you have calculated for Re, in your preliminary work. Use a decade resistor box for Re. (10) Draw the transfer characteristics in Figure B9. V0 (V) (l r Vi (V) Figure B9.——The expected transfer characteristics (dashed line) and the measured trans- fer characteristics (solid line). Adjust Re to obtain minimum hysteresis voltage. Write down this value. Re = (ll) Draw down approximately, in FigureIIU),the shapes of the expected and measured transfer characteristics and the output waveform in the following two cases: (I) Rel "-‘ B;- the resistor required to eliminate the hysteresis). (Rel is the new resistor replacing Re=lK, (II) Re 2 Re 1 + 0.33K l 182 Transfer Characteristics Output Waveform (:5, 1) VO (V) fl VO(V) m 0 + m m u r-( A o V.(v) : (a) 1 (b) V (v) 1) 0 AVOW.) “’i 06 m 11H g = : t f: (c) Vi(V) (d) Figure BlO.--Effect of Re on the transfer characteristics on output waveform (dashed line--expected curves) (solid line—~measured curves). Is Re affecting the loop gain? Is this the reason for the difference in the transfer characteristics and output wave- ftunn when Re is changed? Discuss this with your partner and write down your conclusion. 183 Factors Affecting Circuit Operation Let's look on the Schmitt Trigger as on a "black box" where excess is provided only to the feeding voltages (VCC' Vi) and load connection as depicted in Figure B11. This might indeed be the case when dealing with an Integrated Circuit Schmitt Trigger. e:¥;vcc Trigger Schmitt v I RL Figure Bll.--"Black box" presentation of the Schmitt. Let us investigate the effect of the feeding voltages and loading on the Operation of the Schmitt Trigger. Notes: I. Only one factor will be changed at a time, when investigating its effect on the circuit operation. The other factors (components and voltages) will remain in their nominal values as indicated in Figure B2. II. In order to get the image of the transfer charac- teristics on the sc0pe, the arrangement shown in Figure BG of driving the Schmitt will be used whenever this image of the transfer character- istic is required (on the sc0pe). 184 LoadingiEffect resistor RL __ charact. and expected (Figure 2) output wave- shapes form (12) Compare contacts or call inst. Figure BlZ.--Checking "loading effect" procedure. :: Connect load Observe Trans. Compare to (12) Use the calculated values of the transfer charact. (O), VO(1) from your preliminary work to (le, VTZ, vO draw the "Expected Transfer Charact." in Figure Bl3(a) below in dashed line. Draw down (from the scope) the "Measured Transfer Charact." (Figure Bl3(a) and "Output Waveform" in Figure Bl3(b) in solid lines). For compari- son purposes you may add the nominal transfer function from Figure B7 on Figure Bl3(a). |Vo(v) )vom O Figure BlS.-—Effect of Rs on the transfer characteristics of the Schmitt. ‘9. swat-IE in???” I L. 187 Component Effects on the Operation of the Schmitt Make the following changes in the components' value (one change at a time!) . Draw down in Figure B16 the adequate nominal transfer charact. (from Figure137) and the measured transfer characteristics after a change in a component value was carried out as depicted in Figure 816. (Use a "decade resistor box" for convenience to connect the various resistor values). )vo(v) “vo(v) )vo(v) J .1 ._._ 1 = '7 . l _ *‘V (V) l— 0) RC2 211C2 V1(V) 0 Rel-0.512Cl 1 0 121-0.5Rl (a) (b) (C) 1 VO(V) fl VO(V) o R%=0.SR2 Vi(v) o 12%:=o.3.1>.E vi(v) (d) (e) Figure BlG.--Nomina1 transfer characteristics (dashed line) versus the transfer characteristics when one of the component values of the Schmitt is changed (as pointed out). =Vi(V) 188 Does transistor Q2 remain in the active region (when conduct- ing) if Ré = 10RC ? Explain. 2 2 The Report At the end of the laboratory period of the experiment, you should hand in a report including the following: (a) (b) (c) (d) The experiment procedure sheets with the tables and waveshapes filled out (expected and measured values). Answers to all the questions asked along the experiment procedure. Give possible reasons for differences you've got between the expected and measured values. Solution to the following design problem. What changes are to be introduced into the Schmitt Trigger circuit in Figure B2 in order to feed an elec- tronic decimal counter that has a high input impedance and requires driving rectangular pulses of 6v swing. Calculate the necessary changes. Explain what modifica- tion has to be carried out in the Schmitt circuit of Figure BZ if the driving source can hardly be loaded. ' 8 .l ’5. I. i APPENDIX C THE SCHMITT TRIGGER--ANALYSIS AND APPLICATIONS 189 WM- 'Illli 190 THE SCHMITT TRIGGER--ANALYSIS AND APPLICATIONS (Manuscript--recorded on tape) Hello. A new approach to experimenting in elec- tronic circuits at the college level will be presented to you through the accomplishment Of the Schmitt Trigger experi- ment. My name is Shlomo Waks and I am develOping a model for electronic circuit laboratory experiments. The purpose is to improve your understanding Of the Operation and appli- cations Of electronic circuits, in this case the Schmitt circuit. By use of a systematic approach, I'll try to make you understand the reasoning of the events which will occur during your experimenting process. This model will provide you with means for self- experimenting and learning using slides, audio-tape, flow charts, the oscilloscope facilities, and most Of all, make you use your own brains to calculate the circuit Operation and then investigate experimentally the validity of your design calculations and expectations. When you feel it's necessary, call the instructor for help, but you are encouraged to try to solve the arising problems first by yourself. Time to start. Please Open your Theory Sheets on page 1. If you would like to know where you are heading, what you are going to achieve--read the Objectives. The posttest you will be given at the end Of the experiment is ‘W’ ”71'0“”...“fu9 ‘ I _ I. . - 191 going to find out if these Objectives have been reached. Please turn Off the tape, and come back as you finish read- ing the objectives. Look at slide #1. All these street and road lights—~are they turned on and Off by a man, or is it done automatically according to the intensity Of ambient light? The answer is that these lights are automatically controlled. In the evening when light intensity drops, the artificial lights are turned on, and at dawn they are turned Off. Slide #2 shows a block diagram of such an arrangement. Please turn off the tape, and come back after reading pages 2 and 3. It turns out that the Schmitt Trigger is an elec- tronic circuit which gives an accurately shaped constant amplitude rectangular pulse output for any input pulse above a predetermined triggering level. Slide #3 shows the Schmitt Operation in terms Of the multishape input voltage and the unique rectangular output waveform. Notice that le and VT2 are triggering voltages that determine (1) the two output voltage levels-~the "high" state V0 and the "low" state VO(O). As we have already seen, the Schmitt is usually a portion of an electronic apparatus like a Radioactive Radiation Counter. What is actually happening inside the Schmitt that enables it to square arbitrary input voltage shapes? Let us see how this circuit functions. Look at the basic Schmitt circuit shown in slide #4. The general 192 notation of the two amplifier stages Al and A2 has been chosen on purpose to show that these may be any kinds of amplifiers--transistors, tubes, field effect transistors, or an integrated circuit Operational amplifier. These two amplifiers have to be inverting stages. This basic Schmitt Trigger is a two-stage amplifier with positive feedback pro- vided by the presence of the emitter resistance R as you E' can see in the basic circuit. Let us analyze one Of the most used versions Of the Schmitt: the transistorized Schmitt Trigger Circuit as it appears on slide #5. In this case, two NPN transistors, Q1 and Q2, are the two active components mentioned before in the basic Schmitt as Al and A2. If the input voltage is zero, that means that the input terminal B1 is assumed to be shorted to ground. The voltage drop on RE reverse biases the emitter base junction of 01’ thus keeping it in the cut Off state. Under these circumstances, transistor Q2 has the proper biasing through RC1, R1, and R2 to maintain conduction. It would be worthwhile to use Thevenin's equiv- alent presentation for the collector circuit of transistor Q1. Slide #6 describes it in detail. Notice the expression of Thevenin's equivalent voltage and resistnace in equa- tion (1). Please turn Off the tape, and come back after reading pages 4 through 10 in the Theory Sheets. Let's see on slide #7 some formulas we have just derived through our analysis: The base current IB2 of Q2; the output voltage VO of the Schmitt in the "low" state, 193 which equals simply the supply voltage VCC minus the voltage drop on the collector resistor RC2 of transistor Q2; and finally the triggering voltage VTl' which is the value Of the input voltage that transfers the Schmitt from its "low" state into its "high" state by driving Ql into conduction and Q2 into cut Off. Slide #8 shows the transfer characteristics and the input and corresponding output waveforms of the Schmitt. Notice the three regions Of the transfer characteristics, which are determined by the value Of the input voltage Vi' l. for V. < VT =‘) V = V (O) = Constant low state, i l O O 2. for VTl < Vi < VT2 %> the linear region, and 3. for Vi < VT2 5) Vo = Vo(l) = VCC = Constant high state. Since there is no current flow through RC2, there is no drop voltage on it and the output voltage equals simply the supply voltage VCC' Notice that we get linear amplification when working in the linear region with a small enough input signal, but when raising the amplitude of the input signal as indicated by the dashed-lined input sinusoid we enter the nonlinear portions Of the transfer characteristic. This causes the clipping Of the output waveform shown in dashed lines on our slide. By adjusting the loop gain, the slope of the trans- fer characteristics in the linear region can be changed. If the loop gain is less than unity, the slope AVO over AVi “.3: *— ‘u ‘m.,, 194 is positive. If the loop gain equals unity, the lepe has an infinite value, which means that we have got enough positive feedback just to start oscillations which results in driving the circuit into a stable state by cutting off one of the transistors. For loop gain that is equal to or greater than unity, the linear portion of the transfer characteristics dis— appears, and now the circuit Operates as a bistable device with two stable states. This is the reason that the Schmitt Trigger belongs to the family Of bistable cir- cuits. The Schmitt is mostly used when Operating with a loop gain greater than unity, so the transfer character- istic has the form as described in slide #9. Notice that the triggering voltage VTl which transfers the state of the Schmitt from low to high is greater than the triggering voltage VT2 that causes the reverse transfer from high to low state. The difference between these two voltages ‘le - VT2 is called the hysteresis voltage (VH) of the Schmitt. Please turn Off the tape, read pages 10 through 13, eand come back to hear me right after that. Since we have already got an expression for VTl, (me should start develOping the equation for VT2——the input inoltage which causes the reverse transition Of the Schmitt :frontthe high state back to the low state. In order to do tfliis, let us have a look at slide #10, which shows the enquivalent circuit of the Schmitt in the "high" state. 195 Now transistor O1 is conducting and 02 is in cut Off. That's why the output voltage, without loading, is now equal to the D.C. supply voltage VCC' We neglect the collector cut Off current. This is illustrated in our equivalent circuit by the opened u collector circuit of transistor Q2. Since the cut Off transistor currents are neglected, the base of transistor Q2 has no loading effect on the collector circuit Of tran- sistor 01' SO the equivalent circuit shown in slide #10 F was derived by using Thevenin's theorem. Look at slide #11 to see the way in which this equivalent circuit was Obtained. Notice that the triangle between the collector of transistor Q1 and base of transistor Q2 denotes the attenuator Opera- tion of the voltage divider R2 . Turn Off the tape and come back after reading pages 13 and 14. By developing equations for VTl and VTZ, we have already proved that there exists a hysteresis in the Schmitt action because we have got the value Of VT2 different from the value of VTl, and the hysteresis voltage is defined as the difference between these two voltages. Let us now see on slide #12 a brief summary of the Schmitt Trigger analysis. You will Obtain a great deal of clarification by careful reading of the worked out example on pages 15 through 22. Turn off the tape and come back after studying the example. 196 Now let us see some of the various types of the Schmitt Trigger circuits. Slide #13 shows a Schmitt Trigger circuit with a high input impedance. This feature is achieved simply by using a field effect transistor for the input stage of the Schmitt with adequate bias arrangements for the FET. In the transistorized Schmitt Trigger, the input terminal is almost clamped to the voltage drop on the com— mon emitter resistor plus VbEl’ when Ql is on. Slide #14 shows an arrangement which prevents the input signal from being clamped. When O1 is in cut Off D is conducting, but 1 when Ql conducts D is being cut Off, thus disconnecting l the input signal from the Schmitt. Therefore, the same signal source may drive other circuits with higher trigger levels. In order to get acquainted with the integrated circuit Operational amplifier Schmitt Trigger, please read pages 24 through 26 of the Theory Sheets. After you finish reading, come back. Let us summarize the analysis of the Operational amplifier Schmitt Trigger. Look at slide #15: by means of R1, R2, and VT we determine the triggering ‘voltages VTl and VT2,as seen from the shown equations, of the feedback and triggering voltages. Take a look at the transfer characteristic. When increasing the input voltage from zero, the green line characteristic holds, but when decreasing the input voltage 197 from values greater than VT the red line characteristic 1 is valid. Let us now see a practical industrial circuit that involves a Schmitt Trigger. Please take a look at slide #16. You can see the complete diagram of a twilight switch picked up from the Electronic Application News journal, Volume 6, #6, edited by Inbelec-—Electronic Components Division of Philips India. For details you may refer to this journal. Looking at our slide #16, the portion with the yellow background shows the Schmitt Trigger. In general, an automatic twilight switch serves to switch artificial lighting on or off, depending upon the intensity of the daylight. An essential requirement of automatic twilight switches is a suitable time delay in their Operation. That is to say, the switch should not be sensitive to transient light variations such as lightening flashes or passing clouds. During a storm at night, for instance, a sudden flash of lightening would switch off street lights con— trolled by an automatic twilight switch--if the switch ciid not incorporate a time delay. In the circuit under <:Onsideration, a time delay Of about 20 seconds is achieved but incorporating the Monostable Multivibrator shown in our slide. The switch Operates in the following manner: CHuanges in ambient light conditions vary the resistance of true L.D.R.--the light dependent resistance. This controls time state Of the Schmitt Trigger, which, through a suitable 198 triggering circuit, controls a one shot multivibrator. The states of the Schmitt Trigger and the monostable are linked to two AND gates and an OR gate, which Operate a relay through its driver. The lamp load is switched on, not directly by the relay, but by a power contactor driven by it. Now let us have an overview of the procedure of the upcoming experiment. LOOk at slide #17. It shows a general flow chart of the suggested model for electronic circuits experiments. It is recommended to read the theoretical analysis and prepare the preliminary work before coming to the lab to experiment with the circuit. The preliminary work is actually a quantitative analysis and calculations of the expected values you are going to measure in the lab during the experimenting. If for some reason you haven't prepared the prelim before coming to work on the experiment, you can complete this after utilizing the audio-tutorial facilities right before beginning your measurements on the circuit. As a matter of fact, you can't start experimenting without doing the prelim work because it includes the computation Of some components you have to connect to the uncompleted <:ircuit in order to carry out the required measurements. As you may see on the flow chart, there are three steps Of measuring and observation; namely, measuring the {D.C. Operation, the A.C. nominal Operation, and Observing time effect of source voltages, component values, 199 environment like temperature, and frequency on the Opera- tion of the circuit. At this stage it is recommended to Observe a detailed application of the circuit under experiment, like that Of the twilight switch in our case. After solving a design problem, completing your report, and taking the posttest, the whole experiment procedure is completed. Let me remind you that a great deal of help can be obtained by following the worked—out example in the Theory Sheets. I wish you good luck and successful experimentation. , A—TF—SW" ». 4A ., .-. - 1.. ‘- .I- . l . APPENDIX D Dl~-Pretest D2--Posttest D3--Attitude Test 200 ‘ I M.S.U. E.E. 201 APPENDIX D1 484 Fall 1972 Name PRETEST Circle the correct answer. 1. In a saturated transistor: 1. The collector-base junction is forward biased and emitter—base junction is reverse biased. 2. The collector—base junction is reverse biased and emitter-base junction is forward biased. 3. Both transistor junctions are forward biased. 4. Both transistor junctions are reverse biased. The collector current Ic in transistor Q (Figure l) is approximately: - lVCC=12v RB Rc=lK 100K B IO Q HFE_6O The base-emitter forward _ voltage may be neglected Figure l l. 12 ma. 2. 5.9 ma. 3. 7.2 ma. 4. 0.012 ma. The base resistor R (Figure l) is shunted by a 2.2K B resistor; as a result transistor Q will be in: 202 l. Saturation 2. Active region 3. Cut Off 4. Impossible to determine (from the givens) The voltage between the collector of transistor Q (Figure l) and ground is: l. 7.2 v 2. 12 v 3. 0.1 v 4. 4.8 v Adding a resistor (4.7KQ) between the base B Of tran— sistor Q and ground will: 1. Increase the collector current Ic. 2. Drive the transistor into saturation. 3. Stabilize the collector current Ic concerning ambient temperature changes. 4. All the above answers are incorrect. The Schmitt Trigger can be considered as a flip—flOp circuit because it: 1. Has never two stable states. 2. Can be designed to have two stable states. 3. May be Operated as a free running multivibrator. 4. Operates as a differential amplifier when the lOOp gain is less than unity. 203 ) Figure 2 'If Vi = 0 (Figure 2) then: 2. Q1 and 02 are in cut off 3. O1 is in conduction and 02 in cut Off 4. O1 is in cut off and Q2 in conduction The circuit in Figure 2 is a: l. Monostable multivibrator 2. A stable multivibrator 3. Schmitt Trigger 4. Two—stage amplifier with negative feedback provided by RE' w-w-fiw 10. 204 The hysteresis voltage in a Schmitt Trigger circuit can be eliminated by: l. Decreasing the loop gain. 2. Increasing the lOOp gain. 3. Raising the supply voltage Vcc' 4. Neither of the above answers is correct. Among the three configurations of a single stage transisterized amplifier (C.E., C.B., C.C.), l. The C.E. has the highest power amplification. 2. The C.C. has the lowest voltage amplification. 3. The C.B. has the lowest input resistance. 4. All the above answers are correct. .t'éumnfl. u. . w- .. D Fall 72 APPENDIX D2 * Name POSTTEST (Schmitt Trigger) C C20—————. Rl=22K 0 A I32 Q2 R Vo Re 80K 2 E m 2 1 RE 3309 4 ‘—l (a) J) VT 7 Vi 1 (b) Figure l.--The Schmitt Trigger circuit (a) and its transfer characteristics (b). *The Retention Test is identical to the posttest. 205 206 Circle the most correct answer. Given the Schmitt circuit in Figure l. l. The role of resistor RE is: . TO provide negative feedback to the circuit. TO eliminate the hysteresis of the Schmitt. To provide positive feedback to the circuit. 3 E3 wal-J . TO provide saturation of transistor Ql whenever it conducts. The hysteresis voltage of the Schmitt (in Figure la) can be adjusted by: l. R Cl 2. RC 2 3. R2 4. Answers 1 and 3 are correct. The triggering voltage (VTl) for the Schmitt in Fig. la is approximately: 1. 3.6V 2. 4.5v 3. Impossible to determine VTl even approximately because RC2 is not given. 4. Neither of the above answers is correct. The triggering voltage VT2 (see Fig. lb) depends on the values Of the following components (refer to Fig. la): 1. RC1, RC2, R1, R2, Rs 2. RC1, R5, R1, R2, RE 3. RC1, Rs, RC2' RE, R1' R2 4. RC I RS, R1, C, 11E, R2 1 207 If vi = 0v, then: 1. O1 is in conduction and O2 in cut off, therefore the output voltage VO=VCC=6V. 2. Both transistors Q1 and Q2 are in cut Off. 3. Both transistors are in their active region provided that the lOOp gain is less than unity. 4. Impossible to calculate VO because RC is not given. 2 Inserting resistor Re in series with El (Fig. la) will: 1. Increase V (see Fig. lb) T . Decrease VT 2 3. Increase V 4 am ““ ' . Decrease VT Given the Schmitt Trigger in Fig. l, which Of the follow- ing modifications would you have introduced in order to meet the requirement Of high input impedance (above 0.5MQ): l. Raise Rs. 2. Replace Ql by a tube and make necessary bias arrangements. 3. Replace Q1 and 02 by tubes and make the necessary bias arrangements. 4. Replace Ql by a field effect transistor and make necessary bias arrangements. If the Schmitt in Fig. l is supposed to maintain the same output swing voltage and the same triggering voltages when loaded at the output by RL, which of the following modifi- cations would you introduce in the circuit? 5d 1. Increase C2 2. Decrease R2 3. Increase 4. Decrease Rc 208 9. Lowering R to 10 percent of its value will result in a E change of the following values: (see Fig. lb) 1. le, sz, and v30) 2. Onl in V(l) and V Y 0 T1 3. Only in Vél) and VT2 4. V , V (l) (0) T1 , V0 and V0 T2 10. The input voltage supplied to the Schmitt is shown in Fig. 2a. Sketch the output voltage in Fig. 2b. v. A 1 v /c\ 1/‘\ T (a) l / U L V 0— T2 0 —s—- t )Lvo V(l) O (0) (b) vO . 0 *=— t Figure 2 APPENDIX D3 M.S.U. E.E. 484 Fall 1972 ATTITUDE TEST Mark your answer in the square under the number Of every question according to the following notation: SA — Strongly Agree D - Disagree A — Agree SD - Strongly Disagree N - Neutral 1. I would like to take some other experiments in the electronic lab using the same method as I have used in experimenting the Schmitt circuit. 2. Calculating ahead the expected values to be measured during the experiment made the experimenting more interesting and understandable. 3. The experiment procedure enabled me to proceed by myself without waiting for the instructor. 4. Switching circuits appear to me more understandable and interesting than they did before this experiment Of the Schmitt Trigger. 5. I spent the experimentation time in the lab mainly following the instructions from the experiment-procedure sheets without understanding exactly what I was doing. 209 a P! ‘ —'u.__ \ .v 9| g Have you any comments concerning the Schmitt Trigger experi- ment? Please write them down. 10. 210 Now, after experimenting with the Schmitt circuit I am confident Of being able to handle the Schmitt Trigger by adapting it to new required conditions or locate any malfunctions in its Operation. I have learned more from the Schmitt Trigger experiment than from any other lab experiment in electronics so far. The flow—charts describing the experiment procedure helped me to proceed by myself during the experiment. The slide-tape presentation Of the Schmitt circuit was helpful. I would like to have some additional slide-tape presentations of the Schmitt Trigger applications. APPENDIX D4 M.S.U. E.E. 484 Sec. Fall 1972 INSTRUCTORS' EVALUATION FORM (Schmitt Trigger Experiment) Instructor's name Number of students in section 1. Number of students that finished the preliminary work before the first session (3 hours) was over: 2. Number Of students that didn't complete the experiment: 3. Have you demonstrated to the whole group the circuit Operation? yes no 4. Were you occupied with students' problems during the eXperiment more than in the usual electronics lab experimenting? yes nO 5. Had the students substantial lack Of some prerequisite material or skills? yes no What are they? 6. Difficulties of the students: 211 W _ inmm «wftwqggy - i J '4. J I _ -> lo. 212 Had you any difficulties in instructing this experiment? yes nO . If yes, what were the difficulties? Have you introduced some necessary remedial material to individual students or to the whole group? yes no If yes, what material? Would you prefer this suggested "Model" Of experimentation instead of the "classical" method of experimentation in electronic circuits? yes no Have you any suggestions to improve this "Model" Of exper— imentation in electronic circuitry? Please write them down. Thank you. ‘w‘fi: "hymn”. I APPENDIX E MEASURED RESULTS OF THE SCHMITT CIRCUIT OPERATION 213 214 MEASURED RESULTS OF THE SCHMITT CIRCUIT OPERATION In the following pictures: Figure Figure Figure Figure Figure Figure Note: 1. When waveform is shown, the horizontal axis denotes time (0.2 in/cm). 2. When transfer characteristics are shown, the horizontal axis denotes input voltage vi (lv/cm). 3. The vertical axis denotes, in all the pictures, output voltage v0 (5 v/cm). E5b. Output waveform (Re1=2809). E7. Transfer characteristics of the Schmitt. E9a. Transfer characteristics of the Schmitt with Re:1.lk0, E9b. Transfer characteristics of the Schmitt with ElOa. Effect of Re on transfer characteristics of the Schmitt with Rel=1.l7kQ. ElOb. Effect of Re on the output waveform of the Schmitt with Rel=l.l7kQ. If not mentioned otherwise, Vcc=l2v, Rc =l.llk. 2 215 Figure E5b. Figure E9b. Figure E7. Figure ElOa. Figure E9a. Figure ElOb. Figure Figure Figure Figure Figure Figure 216 ElOc. Effect of Re on the transfer characteristics Of the Schmitt with Rel=2800. ElOd. Output waveform of the Schmitt with Re1=2809. El3a. Transfer characteristics of the Schmitt with load RL-le connected. El3b. Output waveform of the Schmitt with load Rl=lk9 connected. El4a. Transfer characteristics of the Schmitt with Vcc ~7— volts. El4b. Output waveform of the Schmitt with YgE-Volts. Figure 10c. Figure ElOd. Figure E13a. 217 Figure E13b. Figure El4a. Figure El4b. mzuzur-uu Figure Figure Figure Figure Figure Figure 218 E15. Transfer characteristics Ré=5kQ. El6a. Transfer characteristics Ré =2RC . 2 2 El6b. Transfer characteristics R; =0.5RC . l l El6a. Transfer characteristics Ri=0.5R . l El6d. Transfer characteristics '— R2—0.5R2. El6e. Transfer characteristics Ré=0.lRE. Of of of Of Of Of the the the the the the Schmitt Schmitt Schmitt Schmitt Schmitt Schmitt with with with with with with 219 Figure E15. Figure El6a. Figure E16c. Figure El6d. Figure 16b. Figure E16e. —q‘— APPENDIX F IMPLEMENTING THE MODEL IN THE LABORATORY 220 221 IMPLEMENTING THE MODEL IN THE LABORATORY . ..‘u~, f. g.‘ Q“-. g..§wwv ' 0... .y ‘ Figure F2.-—Utilizing the oscilloscope as a measuring instrument as well as a media means. 222 Figure F3.--Getting the input and output waveshapes of the Schmitt circuit on the oscillOSCOpe screen (the writer is seen on the right).