nema 23 is a part of Eurorack sequencer module. Eurorack has taken over the synthesizer community and hundreds of people are building their own Eurorack modules. Michael Forrest designed and built his own Eurorack sequencer module, which does not use strange things like capacitors and chips to store signals.Instead, he did it with nema 23 and some ingenious engineering.
The basic idea of Eurorack sequencers is to store a series of values in some way and play them over and over again. Connect this sequence to a clock and you can get the same sound pattern from the synthesizer. This can be achieved through a circular buffer, using a bunch of FETs and caps in the analog domain, or, in this case, sticking to a piece of paper on nema 23.
The key of this structure is the stepper motor with 96 steps per rotation. This is important because the module is controlled by clock pulses from the sequencer.
Because 96 can be divided by 8 and 16, this means that the sequencer will play in 4/4 of the time.
The built electronic device is very simple. Arduino receives clock pulses and sends step signals to H-driver. It’s very simple, very interesting, and it’s installed on a suitable eurorack-sized panel. nema 23 rotates a paper disc, which is read out by a photoresistor and an LED.