Building DACs and playing potatoes

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I had a class last year with a a simple programming project. We were asked to program TI's MSP432 running energia (the arduino IDE for their ARM Cortex processors) to play various note when a push button was pressed. They let us use the tone libraries to output a square wave at a set frequency. The programming was very simple, too simple.

We spiced up the project by first replacing the push buttons with potatoes. Using a voltage divider and the human body we used capacitive touch to sense when the potateos were being touched.

We wanted to play axel F which requires a sawtooth wave. We built a simple DAC using a resistor ladder, the tricky part was getting the MSP432 to flip the pins on and off quickly. We couldn't finish the project using the Energia Pinwrite command, it was much too slow to work with a resistor ladder. Instead we had to program the registers directly.
Notice my 200 year old oscilloscope in the back, only one channel works. This is what a college budget looks like.

I had to "tune" the program by ear. I didn't feel like working out the proper frequencies on account of the time constraint. You'll hear how off it is in the video.


these are the cheap ebay resistors from china with a high tolerance, but they did the job.

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