Expression pedals are the organist’s primary tool for controlling dynamics and swell box openings. Unlike traditional potentiometer-based pedal controllers that degrade over time, PIPE 2C uses analog hall-effect sensors — solid-state magnetic sensors that detect pedal position without any physical contact between moving parts.
This means zero mechanical wear, consistent response over the lifetime of the instrument, and smooth, continuous control with no scratchy signals or dead spots.
Video Tour
Key Features
- Hall-effect sensing — No mechanical contacts, no potentiometers, no degradation
- 3 pedal inputs per module — Support for swell, choir, and crescendo expression simultaneously
- High resolution — Smooth, continuous analog sensing via ADS1115 16-bit ADC
- I2C chainable — Expand with additional modules for organs requiring more than 4 expression channels
- Solderless assembly — Plug-in connections throughout
Typical Expression Layout
| Input | Function | Common Use |
|---|---|---|
| 1 | Swell expression | Controls swell box louvers |
| 2 | Choir expression | Controls choir/positiv division |
| 3 | Crescendo pedal | Adds stops progressively |
Schematic
PCB Layout
Bill of Materials
| Component | Designator | Quantity | Description |
|---|---|---|---|
| AH49ENTR-G1 | U1, U2, U3 | 3 | Analog hall-effect sensor (SOT-23) |
| ADS1115IDGSR | U5 | 1 | 16-bit ADC with I2C (MSOP-10) |
| KH-2.54FH90-1X4P | U6 | 1 | 4-pin right-angle female header |
| PZ254R-11-04P | H3 | 1 | 4-pin male header |
| 4.7kΩ | R1, R4 | 2 | I2C pull-up resistors (0805) |
How It Works
Each of the three inputs uses an AH49E analog hall-effect sensor. A small magnet is attached to the pedal mechanism; as the pedal moves, the magnet’s distance from the sensor changes, producing a proportional analog voltage. Because the sensor never touches the magnet, there is nothing to wear out and no contact to corrode—the response stays perfectly smooth for the life of the instrument.
The three analog voltages feed an ADS1115, a 16-bit ADC with an I2C interface. That resolution—65,536 steps—covers the full 128-step MIDI expression range many times over, so pedal motion translates into buttery-smooth crescendos with no visible stepping. The digitised values travel to the host over the same 4-wire I2C bus that links the rest of the console, and the module carries on-board pull-up resistors so the bus stays solid. Everything is plug-in: no soldering anywhere in the signal path.
Role in Your Organ
Expression pedals are how an organist shapes dynamics in real time—opening and closing the swell-box louvers, driving the choir/positiv division, and advancing the crescendo pedal that adds stops progressively toward full organ. One module handles all three at once; chain a second module for instruments that need more than three expression channels.
Open Source
Full schematics, PCB layout, and BOM available on OSHWLab: