The Kastle by Bastl
The geniuses over at Bastl in the Czech Republic have outdone themselves again. This time they have created a mini modular synth that runs on only 3 AA batteries not only that you can build it all by yourself with their easy to use kit all for under $100.
Due to its unique digital Lo-Fi sound it can be used to create melodies or insane sci-fi sounds. The Kastle can be used alone or can be implemented into other modular gear.
The oscillator section has 3 sound parameters: pitch, timbre and waveshape – all with voltage control and with 3 different synthesis modes.
It has a main output and a square wave output. Both can be used independently or combined.
The 3 synthesis modes are phase distortion, phase modulation (also known as FM) and track & hold modulation. Each mode utilizes two oscillators.
The Pitch controls the main oscillator, the Timbre sets the pitch of the modulating oscillator and the waveshape depends on the synthesis mode. The waveshape also controls the pulse width of the square wave output from the main oscillator.
Kastle is an open source DIY project which runs on two Attiny 85 chips that can be reprogrammed with an Arduino (google: “programming Attiny 85 with Arduino”).
One chip is dedicated to sound generation while the other handles modulation. Several firmwares for the Attiny chips are available.
Instructions, materials and much more is available here.