fluxharmonium
The fluxharmonium is a digitally controlled, electromechanical synthesizer built from the guts of a Hammond Organ. It is inspired by both the mechanism of the Hammond organ itself as well as the Hammond’s predecessor, the Telharmonium. The Telharmonium, designed an built by Thaddeus Cahill at the turn of the 20th century, is considered the first electromechanical musical instrument as well as the first synthesizer.
The sound of the synthesizer is created by the Hammond Organ’s Tonewheel Generator. This is a large metal construction that houses 91 spinning metal discs. Each metal disc has the profile of a sine wave cut into its edge and spins at a constant speed next to an electromagnetic pickup. Since these wheels create simple waveforms, they can be mixed together to create more complex timbres following the principals of additive synthesis. An organ player would do this with various switches and sliders. The fluxharmonium will allow for more complex mixing of these frequencies using its control system.
The control system is designed around a Tiny RP2040 microcontroller running CircuitPython. The microcontroller accepts MIDI over USB so it can be controlled by standard keyboard controllers or through any software or hardware controller that outputs MIDI data. Incoming MIDI notes trigger individual envelope generators for each tone wheel. The envelopes control digital to analog converters (DAC) which in turn control voltage control amplifiers (VCA) that let the sound of the tone wheel through.
16 tones worth of DACs/VCAs are grouped together on a single “ensemble” voice control card. This makes the design easy to use for other similar instrument designs. The fluxharmonium uses 6 ensemble control cards.
CircuitPython libraries created for this instrument available in the CircuitPython Community Bundle. The first of these is a controller for the LTC166x DAC ICs.
creativecontrol_CircuitPython_LTC166X - GitHub Repo
creativecontrol_CircuitPython_LTC166X - Documentation
creativecontrol_CircuitPython_LTC166X - Daisy-chained DACs Tutorial
