Electronic Instrumentation at the Liberal Arts College Curtis R. Keedy Chemistry Department, Lewis and Clark College, Portland, OR 97219 John C. Abele Physics Department, Lewis and Clark College, Portland, OR 97219 Modern electronic instruments in the physical and biological sciences incorporate integrated circuits to such a great extent that understandine their oneration in terms of fundamental electrical circui& is neariy impossible. Several authors have noted the impact of this "electronics revolution" on teaching electronic instrumentation.'-3 In order for the science student to understand the operation of the instrument s h e is using, a familiarity with the operation of components-diodes, transistors, integrated circuits, and (in some cases) microprocessorcis needed. T o he able to use and to connect these elements meaningfully, the student needs to know about the input, output, and control properties of these components and whether the element is a discrete device or an integrated one. I t is difficult togive this kind of background to the student in a college or university with both limited instructional eouinment funds and limited staff time. o u r solutirk to these problems has been to combine the offerings in electronic instrumentation in the chemistry and physics departments into a tean-taught course that is offered for two, 10-week terms. The first term deals with analog electronics including transducers, operational amplifiers, filters. etc.. and the second term emphasizes digital electronics and &icr&mputers. Besides gaining a n understanding of the various asvects of modern instrumentation, it is also important that the students l a able to apply what they have learned. l'u this end, a two-week laboratory projwt at the end of r x h term enables students to apply some of the techniques and knowledre they have learned ru build instrument systems of their own choice. Course Description The two courses have been designed primarily for chemistry and vhvsics maiors in that a backeround of general vhvsics, . . . including electrical circuits, and two terms of calculus is exvected. Some natural science and hiolom also take the -- maiors " course sequence. There is no required background in computer vroerammine: however. most chemistry and vhvsics students have taken aileast onesuch course and know f;owto operate the terminals associated with the central college computer system. Tables 1 and 2 give the course outline; for thk two terms. The pairing of lahoratory and lectures evidences the strong lahoratory orientation of the course. That is, the primary purpose of the lecture is to prepare the students for the week's lahoratory and to round out their lahoratory experience. There are three hours of lecture and one four-hour laboratory per week. We currently have two lahoratory sections with a maximum of 12 students in each section. Prior to enterim the lahoratorv each week. the students are given a short lectire specifi~all~discussin~ the nature of the laboratorv. l "..nitfalls of which to he aware. and ~ o t e n t i ahazards. Some integrated circuits are delicate and are easily
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'
Journal of Chemical Education
Lecture
Lab
1.
Getting Started: Ohm's Law! input-Output Resistance
1.1 Measurement: I,V,R/Meters .2 Kirchhoff's LawsISeries and
Parallel Resistance .3 Non-ohmic devicesldicdesl 2. ffi lnsbumsnts (TERC)
3. AC Instrumems (TERC)
Iamp~lLED's Voltage dividerlLoading1DC Power supplies CVICC .2 Oscilloscapes .3 AC Waveforms 3.1 Counter-Timer .2 Amplifiergain1Vacuum tubes1 TransistorsIVoltage and Current amplification .3 Amplifier transfer function1 2.1
linearity/Saturation(clipping)/
4.
AmplifierConcepts (TERC)
4.1
.2 .3
EfficiencylOlfsetllnput& Output resistance Amplifier dynamic properties1 Bcde plotISiew ratelnoisel Practical amps Amplifier typeslcment to voltage ampldifferentialamp Power amp1Operational AmplifierlTran~i~tOrS Examination
5.
Spciai Uses of OP AMPS
5.1 .2 Transducers/Typss/Effects .3 Transducersltransferfunction1
6.
D.C. Transducers(TERC)
6.1 Tran~ducer~llnterfacing/Loading/
Working CurveslPower curve
Amplifing .2 Gapacitan&elResistor~lInd~~orsl
RC discharge
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Presented at the 185th American Chemical Society National Meeting Seanle, WA, March 1983. Hargis, Larry G., and Evilia, Ronald F., J. CHEM. EDUC.,59, 414 (1982). Diefenderfer, A. James, "Principles of Elestonic Insbumentation," 2nd ed., W. B. Saunders Co., Philadelphia, 1979, Preface to 2nd ed. Richard J. Higgins, "Electronics with Digital and Analog Integrated Circuits," Prentice-Hall, Englewood Cliffs. NJ 1983. 144
Table 1. Course Outline tor Term 1
.3 7.1 .2
8.
Noise SourcesIFiltering
OiadesIRectifierslRC filters1RL filters DC power supplylRipple1Zener diodes Noise sourceslFiltering (active1
passive) -3 Noise 8.1 Examination .2 AC hansducers1Project
Proposal .3 Transistor Wry 9.1 AC circuitslPhase1impedance .2 (continued)
Bridges AC-DC Summary Proiect Reports .2 icontinued) .3 (continued) Final Examination (written)(Turn In written Project Report at Final) .3
10.1
damaged if wired improperly. The power supplies should he turned on before connectine to breadboarded circuits to avoid transient voltage spikes i h i c h could cause damage to the circuit components. 120 V AC line voltage and high voltages are avoided. Analog Electronic lnslrumeniation The first-term course deals with analog circuits and the measurement of voltage, current, and impedance. Students
Table 2. Course Outline tor Term 2 Lab
lecture
Part 1 1.1 Analog versus digitallbinary1 1. Digital Pulses (Technibooks) (TTL levels, clocks. counters) TTL/outboards .2 7490 decade counted555-clack .3 Logic gatesltruth tebles/Baolean aioebra
Table 3. Student Term ProJecis-Term 1 1. Measurement of human muscle potential using a high input impedance. high gain, electronic filtering system. 2. A direct reading dicde thermometer for temperatures in the 0-10O0C range. 3. A simple curve-hacer for determining characteristics of dicdes and tran~lstorsand an explanation of the use of the Tektronix 576 CuWe hacer. 4. Various special purpose opamp circuits. 5. A simple high impedance detection device for gaseous flame ionization. 6. The characterization of various photo detectors. 7. A thermlstor-based heater canboi system. 8. Various ways to measure the speed of sound in air. 9. DisC~ssionof me theory of operation and a demonstration of a lock-in amplifier detecting adim. oscillating LED with photocell In the presenu, of bright fluorescent room lights. 10. A strobe flash hequency counter. 11. A frequency Mded remote measuring device.
systems part 2 3.1 Debouncers/flipflopsIcounters 3. Inno to Micros (TERC) (runningprewrinen programs .2 MonostableslSchmin triggers on KIM-1) .3 555 revisited/comparators 4. Inno to Micros (continued) 4.1 Examination .2 Organization at a microldatal (connecting to transducers) addressing/control/memo'yI working on their projrcts. Kxamples of the projects performed pr~ce~~~r/regi~ters/al~lb~slPiA by iitudents over the lnst two vears are r i v e n in Table 3. The .3 lntro to KIM programming instructors provide guidance;n the choice of these projects assemblylop codes because students tend to -pick . proiects . that are too grandiose part 3 for the available time. 5.1 110 expansion/application 5. Microcomputer Programming (AAPT) (entering programs and PAIPB Dlgital Electronic lnstrumentatlon .2 Display deviceslscapelX-T single stepping) recorder The second term of the course can he broken down into .3 Subroutines three parts: (1) digital pulses and digital logic; (2) micro6.1 (continued) 6. Writing and Running Simple computer organization; and (3) assembly language proInputlOutput Programs .2 Transducers/A/D/D/A/speedl erammine and interfacine to exneriments. resolution In part-(I), the studenis hecoke familiar with digital elec.3 KIMIDRAMIOSi/VAX tronics by studying TTL digital pulses generated by clocks development syst (555 IC timer), and dehounced pulsers, using 7490 decade 7. Writing Programs Using 7.1 Programming with style counters and seven-seetnent LED'S to count the nulses. These Subroutines (editing on VAX) .2 ASCIIIRS 232120 ma interfacing .3 lntenupts/special addressing experiments are selected from Technihooks ( " ~ u ~ b o oI"k).5 8. Running down-loaded programs 8.1 Possible projects (your Following this introduction to binary systems, digital logic is (wk 7) Writing Subroutines, choice-many suggestions) studied by looking at logic gates (AND, OR, NOR, XOR, etc.), .2 Officehour project discussions Burning EPROM Boolean aleehra, and truth tables. In the laboratorv a two-hit .3 Turn in project proposal binary ad& is constructed from logic gates, 9. Projects 9.1 In part (2), a study is made of a representative single-board .2 Office hourllaboratory microcomputer, the KIM-I.6The organization, data, memory .3 Consulting.. . . addressing, and microprocessor functions are discussed. In 10.1 Project repods in class to. Projects the laboratory, one week is spent learning how to operate the .2 (continued) .3 (continued) computer, place data into memory locations via the keyboard (Wrinen Project Repans turned in at Final) and use the I10 ports to place data into the computer and get
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become familiar with volt-ohm meters, digital multimeters, and oscilloscopes. Also, they learn how these instruments may affect the measurement (i.e., the significance of input and output impedance). Voltage regulators and operational amplifiers packaged as integrated circuits are incorporated into student-constructed circuits. For making connections to these IC's, solderless breadhoards are used. Operational amplifiers are studied in detail and are used as voltage followers, inverting and non-inverting amplifiers, and integrators and differentiators. In addition, the application of operational am~lifiersfor non-linear functions and current-to-voltaee co&ersion are discussed. Since the direction of this coursek toward application, transducers are treated as devices that allow physical parameters to he converted into electrical signals. Several types of both active and passive transducers are studied in the laboratory. Thermistors, thermocouples, reversed biased diodes, and photocells are used. Transducer working curves and &ohle&s of loading are investigated. Diodes, rectifiers (half-wave and full-wave), and filters are used in constructing a DC power supply from an AC source. Finally, hand-pass filters are studied as a method of obtaining a signal from a noisy source. A number of the laboratories are modules that are obtained from the Technical Education Research Centers.' Finally, a student-selected project is performed during the last two weeks of the course. The laboratow.is open - four hours per day during that time so students can spend extra time
data from the computer. During the next week, the students run nrewritten Droprams (which are burned into EPROMS (~r&ahle-~ro&ammable-kead-only-~emory)) to carry out various exneriments. These exneriments include usine the computer as a time-counter to determine the period of a ~ e n d u l u m as . a wave-form eenerator with the o u t ~ u dist played on the oicilluscope, and as a tmnsienr recorder in whirh a short-term sirnd ran be ca~ruredand disnlaved re~etitivclv on a oscillosc&e. These functions are used to show the ve;. satility and utility of a microcomputer as a laboratory instrument. In part (3), the students begin writing and running their own programs on the microcomputer. They are led into assembly language programming gradually by entering prewritten programs and stepping through the program to see the effect on data registers and memory locations as each step of the program is executed. They are also given a set of prewritten subroutines on EPROM to do simple input and output operations that they may use in writing their programs. As the students become more proficient in using the computer system, the programs requested get more complexuntil the last 8 Eliot Street. Cambridge, MA 02138, (617) 547-3890. Supplier: E & L Instruments, Inc., 6 1 First Street, Derby, CT 06418, (203) 736-8774. KIM-I/SYM/AIM products from: Perry Peripherals, P.O.BOX 924, Miller Place. NY 11764, (516) 744-6462.
Volume 62
Number 2
February 1965
145
Table 4. Student Term Prolects-Term 2 1. Home-bulk analog-tdigitaiconverter. 2. Monitoring the discharge of a banery. 3. .. A temoerature ~.~ controller usino a non-linear. variable wise width ~
7 -
~~~
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~
feedback undw sonware control. 4. Sening up an Ohio Scientific Inst. computer as a generalgurpose laboratory instrument that communicates with the campus computer. 5. Measuring the integrated daily solar intendw. 6. Interfacing a Cary UV-visible spectmphotometer. 7. Making a digilal clock from 7400 chips and a 555 timer. 8. Measurement of the temperature fluctuationsof a 'Yonstant"
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tamneratwe ~. - - room.
9. 10. 11. 12. 13.
14. 15
16 17.
~
~~
Conslrunoan of a sman scalar lo measure radioacuve half- ife. Meas.rement of the ime oependence of the pernod of a damped "simple" pendulum. Understanding and using a UART. Using a large array of phototransistors and a KIM1 microcomputer to build a position and time table b r a car on an air track. A microcomputer-basedaudio oscillatw with analog hardware control of amplitude and frequency. Interfacinga microcomputer to a gas chromatograph and writing same 01 me m a y s r sonware Develop ng a dfgltal clock uslng a 4 M - t microcomputer Learnmg lo use an L S I / l l microcomputer in the laooralonl me design and construction of a hybrid programable microcomputercontrolled wave form generator.
nroeram thev write is essentially the transient recorder they h e ; in part"@). Finallv. students devise and execute projects that incorporate the materials they have learned into system of their own interest. Examples of the projects which have been performed during the fast two ye& i r e given in Table 4. A diamam of the computer system is given in Figure 1.The KIM-] &icroromputer has a (iju2 micr"processor (the same as the Commodore. Apple, SYM, AIM, and OSI computersl. to ~the KIM and has a A mirroinstrument ~ - - ~ ~ hoard7 - ~ ~ is - attached - - ~ ~ ~ digital-to-analog converter, a comparator, an op-amp, 1K of RAM, and a socket for 2 K of EPROM. This system allows analog data to he digitized (with software) and gives more memorv for storine nroerams . .. and data The KIM cost is about 4180 and the mirro.instrurnent hoard (kit form) cost is about Sl2U. There are six of these stations in the inhomtorv. Each station also has a power supply (f12 V a t 100 mA, 5 v a t 1A) that costs about $50.8 In order to facilitate student access to the KIM computers nnd gi\.e more time to write programs, these stations have been linked to the campus romputer system WAX 11/780) where there are 3U or more rerminals available to students. Figure 2 gives a diagram of the setup. The assembly language programs arr written and srured on the VhX system. When the Htudent is in the laboratory and ready to run a program, s h e can get the program from VAX through an Ohio Scientific (OSI) computer (8PDF-48K, dual floppy disk, $3,500). The OSI computer will then assemble the program, check for errors. and store it on a flonnv disk. The Dromam can then he transferred to the KIM &&ory via an RS-532 line from the OSI comnuter svstem. Facilities are also available for burninastudent programs into EPROM.
a
~~~~
~
SC SY AN,
AN,
Figure 1. Diagram of the computer system ORiGiNAL
SYSTEM
ENHANCED
DEVELOPMENT SYSTEM tarmlnals
..
~
T
T
~
EACH INDIVIDUALLY PROGRAMMED IN MACHINE CODE
.,
Discusston
Students have been very quick to apply the techniques learned in these courses to other laboratory courses where microcomputer control, data gathering, and data processing are involved. Kinetic studies on the UV-visible spectrophotometer and peak integration from a gas chromatograph have been done in subsequent chemistry courses.
'Supplier: Cambridge Development Laboratory, 36 Pleasant St.,
Watertown, MA 02172, (617) 890-8076. Supplier: Power One, Inc., Power One Drive, Camariilo, CA 93010, (805) 484-2806.
Barnall. Dennis, "Analog and Digital Electronics for Scientific Application," Breton Publishers. North Scituate. MA, 1982. 146
Journal of Chemical Education
KIM
KIM KIM
KIM KIM KIM -
SINGLE BOARD /I-COMPUTERS WITH A/D CONVERTERS
Figure 2. Set-up fw linking stations to campus computer system. Since students tend to pick projects that are too ambitious, they should consult carefully with the instructors prior t o beginning projects. Unless reasonable end points are established, student enthusiasm can turn to frustration. The project should he broken down into modules and each module tested before the modules are out toeether and tested as a svstem. An unanticipated beiefit cake irom having chemis;ry and nhvsics students in the same class. \Ye feel that as a result the &dents have gained respect for each other and can better appreciate the approaches the others use in solving laboratory problems. Further, they can see that there is not any real difference in abilities between them. Acknowledgment
The development of these courses has been sponsored, in part, by an NSF-CAUSE grant. We would also like to express our gratitude to William Moseley who helped develop and test much of the VAX-OSI-KIM Software. A recent textbookg closely follows the outline of this course.
