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Session 3532

A Microcomputer-based Logic Signal Generator and Recorder/Analyzer for a Beginning Digital Electronics Laboratory

J. Sherwood Charlton, Jeffrey J. McFarland, James D. Shuffield University of Arkansas

The Electrical Engineering Program at the University of Arkansas is in the process of integrating laboratories with each required course instead of having a separate sequence of laboratories. This creates some problems with regard to our beginning digital systems course. This course covers binary and complement arithmetic, Boolean algebra, combinational logic, sequential logic, and the various digital IC’S simpler than microprocessors. The course includes the study of many of the TTL, and their CMOS equivalent, digital IC’s including terminal properties and other data sheet information.

The beginning digital systems course is arranged so that it can be taken as a corequisite with the first electric circuits course; portions of the digital course requiring Kirchhoffs laws, Ohm’s law and first-order RC circuits are presented after those topics are covered in electric circuits.

Coming this early in the student’s electrical engineering education, the student has not been exposed to pulse generators, logic analyzers, or even oscilloscopes. Normally under these conditions, a digital trainer would be used. Most digital trainers provide only a clock waveform, a certain number of switches to supply steady logic levels and perhaps a push-button switch as inputs to a test circuit, To record the output(s) of the test circuit, LED’s are provided. While this is adequate for combinational logic circuits it is a poor substitute for studying sequential logic circuits and provides no permanent record.

It was desired to have a extremely user-friendly, programmable, logic-level signal generator with several outputs and the ability to simultaneously record several digital signals. It was also desired to keep this system inexpensive and to have a permanent record of test circuit input/outputs signals.

SOLUTION

Our solution is based on the ready availability of outdated computers and dot-matrix printers. As the computer labs have been upgraded, a surplus of unused computers and printers has occurred. This equipment was destined for storerooms or surplus property ofilces, The system described herein is based on 80286 computers with EGA graphics, but could be adapted to more or less powerfhl platforms. The printers are generic, ink-ribbon, dot-matrix printers.

As can be seen in Figure 1, the students may define up to 8 inputs to his test circuit which is built on a prototyping board. Logic levels of up to 8 points in his circuit maybe recorded and displayed on the computer screen and printed, The interface between the computer and the prototyping board is through a parallel port of the computer, The student uses primarily the cursor keys, the 1 or O key for a TTL 1 or O to

$i!fiiii’ }- 1996 ASEE Annual Conference Proceedings ‘n,,,yyHll’,?

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McFarland, J. J., & Shuffield, J. D., & Charlton, J. S. (1996, June), A Microcomputer Based Logic Signal Generator And Recorder/Analyzer For A Beginning Digital Electronics Laboratory Paper presented at 1996 Annual Conference, Washington, District of Columbia. 10.18260/1-2--6190