This weeks project is a simple 4-step sequencer based around a 4017 decade counter chip. The basic schematic is based on this circuit, using a 555 timer as a clock source:
I changed it a bit by having the 4017 outputs drive transistors that switch current to the pitch pots (instead of turning on LEDS). Also, I triggered the chips RESET on step 4 instead of using all ten steps.
The sound is generated by a toy piano that I hacked up. Each of the four steps in the sequencer is routed through a 100K pot that varies the resistance to the piano and triggers different notes. I also threw in a touch point for garbling up the sound.
Here it is in action: