If Not Us, then Who?

ptc board
Solar bike power transfer controller board, configured as a function generator. There are already test points on the board, to which a scope probe can connect. The logic voltage regulator is bypassed, and just brought out to a USB connector. To provide a floating waveform, the whole thing is powered from a USB charger battery (cylinder near top left).

“If not us, then who?”

This is a tag line from one of my favorite movies, Machete.

Recently, I needed a function generator to help test some oscilloscope software I’m working on.  Unwilling to shell out for a formal piece of equipment, I decided to build one out of a PICAXE.  It could have been wired on a solderless breadboard, I suppose.  Or a perf board.  But then I realized that I had 4 more blank fabs of the solar bike power controller, already laid out for a PICAXE.  It seemed a waste to use basically a $20 board to wire up such a simple thing, especially since just the tiniest fraction of the board would actually be used.

But then I thought, “If not for this, then what?”  The extra proto boards were just lying around doing nothing, and I had already decided to make a major revision to the board. At my age, I find myself asking this question a lot – what am I saving it for?

Here are some pictures of the waveforms captured by my software. It’s got a long way to go, but having a function generator handy will accelerate development greatly.

5 mS / div
At a slow sweep rate, the waveform looks like this.
5 uS / div
The waveform was designed to be useful at higher sweep rates, also. Each spike actually has a high-pass RC filter on it, to show features at this sweep rate, which is 1000 times faster than the previous picture.
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