When microcomputer-based controllers first became available in
automobiles, General Motors made a set of diagnostic codes available
through a connector under the dash. Although most, if not all,
manufacturers now produce these codes in a standardized manner,
originally they did not.
The coded numbers in GM cars were transmitted as a series of
voltage pulses. The dealerships had specialized equipment to read
these codes to aid in the diagnoses of engine problems, but home
auto mechanics did not. I received a call from an individual who
wanted to develop a simple handheld instrument that deciphered the
coded pulses and displayed the result. He asked if I would build one
prototype for him as a feasibility model.
The job was simple. I designed a simple logic circuit using 4000
series CMOS because the device was powered by 12 volts. My client
had a prototype enclosure that resembled a small calculator, and I
built the prototype so it would fit into his enclosure.
This is an example of a simple job that required no more than two
days of work.
