Mini synth I built based on the Atari Punk Console. Instead of two 555's or a 556 this uses one 555 and a 4013 D-type flip flop. It has two momentary pitch shifters (up + down) three pots controlling different frequencies, a three way switch for different sounds, and a volume pot. The output is standard 1/4 inch.
It's surprising how much I could fit into such a small space. I considered using LDR's but decided against it as this would prevent me from playing it in the dark.
Second half of the video the synth is running through Autotune playing C minor scales. You can also target the Autotune notes via MIDI keyboard and use the mini synth as a sound source.