One of our favorite musical hackers, [Look Mum No Computer] is getting dangerously close to building a computer. His quest was to create a unique drum machine, inspired by a Soviet auto-dialer that used rope core memory for number storage. Rope memory is the read-only sibling to magnetic core memory, the memory technology used to build some beloved computers back in the 60s and early 70s. Rope core isn’t programmed by magnetizing the ceramic donuts, but by weaving a wire through them. And when [Look Mum] saw the auto-dialer using the technology for a user-programmable interface, naturally, he just had to build a synth sequencer.
The basic technology is to monitor the ferrite ring using a primary winding connected to a comparator. Then run the signal wire through some of the rings, and use a 555 to send an oscillating signal through it. The individual bits, AKA ferrite rings, pick up the signal and trigger the comparator. (Using transformers as bits, what fun!) So for a working sequencer, each ferrite ring controls an instrument. Ring 1 is a kick drum, ring 2 is a snare, etc. Then each wire is a different step, and they get powered sequentially. Wire the bit outputs to your instruments, and then weave your beats. It’s already the most unique sequencer we’ve ever seen, but there’s more.
Since he used really big ferrite cores, there was plenty of room to take beat submissions from his community, so there’s eight different beats “programmed” into this sequencer. And to switch between them? Looks like [Look Mum] is using a step-by-step module from the old phone system. Dial-a-beat!