I bought a Teensy 4.1 with the intention of learning new levels of audio electronics, and while this synth project is not entirely complete, as with all such projects, it is complete enough to talk about. I was really excited to try the PJRC audio system design tool, which is great! The PJRC libraries quickly became intuitive.
And it almost goes without saying that this device, like its pedecessors, is made of many recycled materials: wood, wires, black plastic panel, and potentiometers are all from salvage. I also bought a few other handy go-alongs, including:
- my fave, the MPR121 capacitive breakout board (under $3) which can best be understood via a thorough Adafruit tutorial;
- a tiny OLED display (under $5), made useful by the Tiny4kOLED library; and,
- an inexpensive I2S DAC, which took a moment to understand, but ended up being quite simple in this particular (Teensyduino) context.
As the nodes below suggest, the core of this synthesizer is a frequency-modulated sine wave, sent through a filter and an envelope. Translated to hardware, the recycled Rheem organ keys play predefined frequencies (~C4 through ~B4), but a modulating waveform is always messing with these frequencies, as controlled by a simple potentiometer.
Several more pots control a filter, which is itself modulated by a waveform! Separate physical controls for lowpass, bandpass, and highpass outputs increase the sense of infinite possibilites. I also control "room size" of a reverb effect and the "attack" phase of an envelope, along with a master volume control. I am contemplating more features, such as the ability to swap waveform types with a rotary encoder, and options for control voltage outputs.
Here's a demo of the Smoo (a word based on my niece saying "smooky" to mean "spooky"), plugged into a heavily reverberating DIY amplifier in my 'lab':
Finally, here are some fruits of these hilarious 'labors,' including audio files, more pictures and videos, and the code as of this writing.