To be able to play a bit on the synthesiser, I made a simple keyboard out of some old scrap I had in the junk bin. The construction is very simple: a potentiometer as voltage divider between rail and ground and a push button between output and wiper. Each button is tuned with the potentiometer and output is connected to the VCO. I made a full octave, starting with C, which gives 12 buttons and 12 potentiometers. Its was a bit boring to assemble, but works great.