The main circuit board is now largely built and working. It contains the Teensy and its audio add-on board, four shift registers to facilitate communication with the modules, and eight 12-pin female headers for the modules to connect to. Each module also contains four shift registers, as well as a number of sockets and potentiometers.

In total, the main circuit can handle up to 64 potentiometers (eight per module) and 64 sockets (again, eight per module). The Teensy also receives an eight-bit ID code from each module, so that it knows which module is mounted in which slot.

The wiring and soldering has been tedious but successful, with the only mistakes coming when I attempted to watch YouTube videos at the same time. It would make a lot of sense to use printed circuit boards rather than stripboard for this project in future, but the constantly evolving nature of the design means stripboard is still the most suitable method for this version. Also, I've never made a printed circuit board before, and it looks complicated...

The only unforeseen issue so far was that the Teensy didn't fit underneath the modules, so I had to move it to a separate circuit board. There is a "master" module in the synth, which always needs to be present, so I moved that to sit permanently at the far end and cut away part of its circuit board so that it could fit next to the Teensy. This still left me with room for seven removable modules.

As well as the main circuit board, I've now built three modules: the "master" module (containing the main output stage and future access to things like the keyboard notes), an oscillator, and a white noise source. These are all working fine, and the focus is now on creating lots more modules as quickly as possible. Here are some of the modules I want to try to have done by the Hackaday Prize deadline:

• Master (done)
• Noise / sample and hold (done)
• Oscillator (done)
• Amplifier
• Low-frequency oscillator
• Envelope generator
• Resonant filter
• Mixer
• Bit-crusher / distortion
• Delay / reverb
• Wavetable oscillator

The synth is already producing some distractingly interesting sounds - I'll post a video soon.