Mudras

Hand-controlled CV sequencer firmware for mudras.ino.

Overview

Mudras is a gestural sequencer for modular and CV-based instruments. It uses a VL53L0X time-of-flight sensor to track hand position, converts that motion into either quantized pitch CV or smooth linear control voltage, and records/playbacks sequences in sync with an external gate or clock.

The name comes from mudras — hand gestures used in classical Indian dance and yoga. Like their namesake, each hand position produces a distinct musical expression.

Features

• Hand-position control with a VL53L0X distance sensor
• External clock/gate input for step advancement
• Record and playback modes selected with a button
• Variable loop lengths from 2 to 64 steps
• 7 quantized musical scales plus 1 linear CV mode
• 12-bit DAC CV output on PA4

Hardware Connections

Mudras Uses a STM32G431, but it will work and this code is compatible with any STM32 Chip that has a built in DAC

Pin	Function
D4	Record/play button input (INPUT_PULLUP, active low)
D5	External gate/trigger input, falling-edge interrupt
PA0	Loop length knob
PA1	Scale selection knob
PA4	12-bit DAC CV output
SDA/SCL	I2C connection to VL53L0X sensor

How It Works

Clocking

• An external trigger on D5 advances the sequencer.
• The interrupt service routine only sets a flag.
• Step advance, record, and playback logic are handled in the main loop.

Recording and Playback

• Hold the D4 button to record.
• Release the D4 button to play back the stored sequence.
• Entering record mode from playback resets recording to step 0.

Sensor Mapping

The distance sensor is read continuously:

• In scale modes, hand distance is mapped to a note index.
• In linear mode, hand distance is mapped directly to the full 12-bit DAC range.

Scale Modes

The scale knob selects one of 8 modes:

Mode	Behavior
0	Major
1	Dorian
2	Minor Pentatonic
3	Harmonic Minor
4	Diminished
5	Whole Tone
6	Chromatic
7	Linear CV (no quantization)

Loop Lengths

The loop length knob selects one of these sequence lengths:

• 2 steps
• 3 steps
• 4 steps
• 8 steps
• 16 steps
• 32 steps
• 64 steps

Signal Path

Scale Modes

1. Hand distance is mapped to a scale index.
2. The scale table converts that index to a note.
3. The note is converted to volts using 1V/octave.
4. Voltage is converted to a 12-bit DAC value.
5. The DAC outputs CV on PA4.

Linear Mode

1. Hand distance is mapped directly to 0-4095.
2. The raw DAC value is recorded or played back.
3. The DAC outputs smooth unquantized CV on PA4.

Dependencies

This sketch depends on:

• Wire
• Adafruit_VL53L0X
• ResponsiveAnalogRead

Firmware Notes

• DAC output uses 12-bit resolution.
• I2C is configured for 400 kHz.
• The sequencer stores up to 64 steps in memory.
• The external gate input is expected to be level-shifted/protected before reaching D5.
• The step counter starts at -1 so that the first incoming gate increments it to step 0 before any playback or recording happens.

Glossary for Beginners

If you are new to modular synthesis, these terms appear throughout the code and documentation:

• CV (Control Voltage): An analog voltage signal used to control a parameter — such as pitch or filter cutoff — in modular synthesizers. Mudras outputs CV on pin PA4.
• 1V/Octave: The standard relationship between voltage and pitch in modular synths. Each 1-volt increase raises the pitch by one octave (12 semitones). This is how midi_note_to_volts() works in the firmware.
• Gate / Trigger: A short voltage pulse used to clock or advance sequencers. Mudras receives a gate on D5 to step forward.
• Sequencer: A device that stores and replays a series of notes or CV values in order, synchronized to a clock.
• Quantization: Snapping a continuous value (like hand position) to the nearest note in a musical scale. Scale modes 0–6 do this; Linear mode (7) does not.
• DAC (Digital-to-Analog Converter): Hardware that converts a number (0–4095 in 12-bit) into an analog voltage. The STM32G431's built-in DAC on PA4 is used here.
• Time-of-Flight sensor: The VL53L0X measures distance by timing how long a laser pulse takes to bounce off your hand and return.

Usage Summary

1. Power the module and connect the VL53L0X sensor.
2. Feed an external clock or gate into D5.
3. Set loop length with the knob on PA0.
4. Choose a scale or linear mode with the knob on PA1.
5. Hold D4 and move your hand over the sensor to record steps.
6. Release D4 to play the sequence back.

File

• Main firmware: mudras.ino