The controls are connected to two Arduino Pro Micro microcontrollers that communicate via the I2C communications protocol, one microcontroller handles the sequencing and the other functions as a synthesizer using the Mozzi library. There are three layers of control, one for each voice. For an overview see Beat Machine v 0.3 Guide. Low-cost tactile switches are used to enter step-sequences and to access the various layers of control. A ring of programmable LEDs (light emitting diodes) indicates sequence pattern and layer information so the user can see where steps have been programmed to sound and which synthesizer voice these correspond to. The first voice is optimized for a bass drum-like tone (noise source has high frequency rolled off), the second voice is optimized for a high-hat like tone (noise source has low frequencies rolled off), the third voice is full-range and is intended to approximate a snare drum. Each synthesizer voice is made up of two oscillator elements that can be blended together or sounded in isolation using the balance control, the first is a sine waveshape and the second can either be a sawtooth waveshape or a noise source. When using sine and saw these can be detuned by up to an octave and then pitch-fall and the attack/release amplitude controls can be used to sculpt the overall sonic character of each voice. Pitch, volume, and distortion controls are also available. See also:

• Andrew R. Brown, John R. Ferguson; Beat Machine: Embracing the Creative Limitations and Opportunities of Low-Cost Computers. Leonardo Music Journal 2020; 30 8–13. doi: https://doi.org/10.1162/lmj_a_01087
• Andrew R. Brown, John R. Ferguson; Enhancing DIY musical instruments with custom circuit boards. Proceedings of the 11th Workshop on Ubiquitous Music
• For a more informal discussion see ‘Professor Andrew Brown and Dr John Ferguson discuss DIY Electronics and Post-digital Practice in the context of their “Beat Machine” project’: https://www.youtube.com/watch?v=X4lFmh8l_Gs