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Simplicity in circuitry was the design direction. Zero mass (firmware only with no physical components) would the ultimate achievement. This instrument doesn't have any front panel controls because the user interacts via an RS-232 terminal program at 9600 baud.

I needed a frequency meter for my experiments in Nondu, Thailand, where I really don't have room for a lot of instruments. I wrote some straight forward code to read the 16 bit counter in the AT90S2313 after period of time, which was determined by running a timing loop. By the way, I tried various approaches using interrupts from the 8 bit timer to set the counting interval, but found timing uncertainty resulted in intolerable jitter in the measurements, to as inelegant as it is, timing loops turned out the be give the best results. The results of the counts are converted to ASCII and sent to the terminal. After finishing the frequency meter, I realized that only half the Flash ROM was used and that I could fit a handy pulse generator program I found on the web into the same chip, but having two instruments in one. The result is a combined counter and frequency meter. The chip flips between the two programs, The only things common between the two programs is some initialization and some of the se-ri-@l port I/O code. The pulse generator firmware is pretty much as originally published, except that I modified it to drive a resistor network so as to allow the pulse output amplitude to be selectable.

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