[Atdiy and Whisker] aka [The Tymkrs] have created a MIDI controlled 8 note modular synthesizer. (YouTube link). The project was designed to highlight some of the modules they have available at their Tindie Store. Essentially, the synthesizer is 8 classic Atari Punk Console (APC) tone generators. Each APC is made up of two 555 chips, rather than the 556 used in the original design. The APCs are tuned to a Pentatonic scale, with the 8 notes covering 1.5 octaves. [Whisker] added a single potentiometer which controls all 8 of the monostable oscillators at once. Tweaking this knob gives the synth that classic Atari Punk Console sound we’ve all come to know and love.
The 8 APC outputs are routed to once side of an AND gate. The other side of the AND gate is connected to a 74hc595 shift register. A Parallax Propeller processor converts MIDI note data into a serial stream that can be daisy chained across several ‘595 shift registers. The outputs of the 8 and gates are mixed to a single combined output, which goes out to [The Tymkrs] studio amplifier.
Like many [Tymkrs] videos, this one ends with a MIDI driven jam session, outlining how the circuit would sound in a song. Click past the break to see it all in action!