I needed a rotary encoder — I pulled a cheap one out of one of those “49 boards for Arduino” kits you see around. Not the finest encoder in the land, I’m sure, but it should do the job.

At the heart of the device is a AD9833 waveform generator; with the Arduino, rotary encoder, and 16×2 LCD providing an interface to control it over SPI. Unfortunately, the AD9833 doesn’t have ...