Optical Touch Mini Synth
Listen to Sample
Optical Touch Mini Synth
A seven voice string, drum, and tone digital synthesizer with 7 touch pads and an optical proximity sensor.
The optical proximity sensor does effects bending.
Three control dials select the pitch, instrument, and distortion effect.
The technology is STM32 DMA DAC signal generation and an active filter, producing 16 bit single channel (mono) sound.
The software is Arduino compatible and available for download below.
Design Documents
| Schematic Diagram | schematic_j210_optical_touch_mini_synth.pdf |
| Bill of Materials | bom_j210_optical_touch_mini_synth.pdf |
| PCB Gerbers | gerbers_j210_optical_touch_mini_synth.zip |
| 3D Models | optical_theremin_mechanical.zip |
| Source Code | code_j210_optical_touch_mini_synth.zip (original release) code_j623_optical_touch_mini_synth.zip (current release) |
Specifications
| Power Requirement | 5.0V 500mA USB micro jack |
| Output | Audio line level, 3.5mm stereo jack Requires powered speakers or amplifier. |
Setup
Connect 5V USB power source and 3.5mm stereo audio cables.
The audio output is the same on both left and right channels.
Controls
Click for bigger image
 Touch pads | Play the instrument |
 Pitch | Sets the frequency range for the touch pads |
 Wave | Selects the instrument: tone, string, drum |
 Effect | Selects the instrument variant |
 Proximity sensor | Varies an instrument parameter |
Instruments (Wave knob)
| Tone | A sine wave tone with an envelope.
The Effect knob selects the ADSR envelope. The Optical sensor varies the tone frequency. There are 3 scales, selected with the Wave knob: - Heptatonic (C,D,E,F,G,A,B) - Pentatonic minor (C,E♭,F,G,B♭,C+1,E♭+1) - Pentatonic major (C,D,E,G,A,C+1,D+1) |
| String | A string instrument.
The Effect knob selects the base string decay. The Optical sensor varies the string decay. There are 3 scales, selected with the Wave knob: - Heptatonic (C,D,E,F,G,A,B) - Pentatonic minor (C,E♭,F,G,B♭,C+1,E♭+1) - Pentatonic major (C,D,E,G,A,C+1,D+1) |
| Sound Effects | Five basic sound effects.
- Pew Pew - Bell - Drip - Drop - Space gun The Effect knob selects the sound effect group. The Optical sensor varies one of the sound effect parameters. |
Indicators
| CLK | Normally on, indicates the audio bit clock is running |
| DMA | Gets brighter as DMA load level increases |
| ERR | Audio processing overload - this won't happen unless you modify the instrument code |