Something I’m excited about these days is rhythmically interfacing incompatible musical components like my analog modular synthesizer with a Casio SK1 Keyboard and a Barbie Karaoke machine. One tool that has helped me do this is the 8 step, 4 channel sequencer pictured above. The sequencer is based on a 555 timer and the 4017 decade counter. It’s got a low part count and is easy to build. Mounting all of the switches was by far the most difficult/expensive part but beside that it’s easy/cheap.
The schematic below is what I used for the sequencer (click to enlarge). I’m sure there’s room for improvement, but this has worked so far. 
I’ve rebuilt this circuit a few times for different projects. In some cases it is better to remove the 4016 IC and use relays. Or sometimes you can just use transistors as switches. Here’s a schematic sent to me by SUBBS (click to enlarge). He’s adapted the sequencer design to function as a multi channel, rhythmic tone generator. Looks pretty cool.
Here’s a Speak&Spell with a built in 8 step, 1 channel sequencer based on the schematic above. Lots of possibilities.
More:
