Apple II Modular Synth Control
Some time ago, Joshua Coleman Makes built a modular synth rack based on a 555 square wave generator as one of the modules, along with an Arduino-based VDCO, or Voltage Controlled Digital Core Multimode Oscillator. More info on the Arduino bit can be found here on GitHub, but the short story is that between these two modules – and whatever else he hooks up – the rack is able to generate a wide variety of sounds.
The “whatever else” in this case is an Apple II computer that pipes in analog voltages with the help of a DAC pack originally meant for model trains. This DAC, which is quite hefty by today’s standards, regulates voltages via an 8-bit input from the computer for modification of the unit’s sounds output. Coleman wrote two BASIC programs on the Apple II to facilitate music making, including one that plays “Mary Had a Little Lamb,” and another that turns the Apple keyboard itself into a musical input.
The video below goes over the build concept in more detail, and it’s fun to see a DIY modular synth setup controlled by this type of vintage equipment. Given the size of the DAC unit – and what one likely cost at the time compared to inexpensive chips of today – it’s interesting to consider what hackers of yesteryear had to go through to create awesome electronic effects!