Eight-position hall-effect sensor arrays for pedalboard note detection. Chain four modules for a complete 32-pedal AGO specification pedalboard.
Video Tour
Overview
The pedalboard is the foundation of organ playing, and reliable note detection is critical. PIPE 2C’s pedalboard sensor modules use HX3144 hall-effect digital switches—contactless magnetic sensing technology—to detect which pedal keys are depressed, with state read through a PCA9555 16-bit I2C I/O expander.
Each module provides 8 sensor positions. Chain 4 modules to cover a complete 32-pedal AGO (American Guild of Organists) specification pedalboard, the standard for concert and church instruments.
Key Features
- 8 HX3144 hall-effect sensors per module — One per pedal key
- PCA9555 I/O expander — Reads all 8 sensor states via I2C
- Contactless detection — No mechanical switches to wear out or bounce
- DIP switch addressing — EU-03KS 3-position DIP switch for I2C address selection
- 4 modules = 32 pedals — Full AGO specification coverage
- I2C chainable — Standard 4-wire connectors between modules
Schematic
PCB Layout
Bill of Materials
| Component | Designator | Quantity | Description |
|---|---|---|---|
| HX3144ESO | U2, U6–U12 | 8 | Digital hall-effect switch (SOT-23) |
| PCA9555PW,118 | U5 | 1 | 16-bit I2C I/O expander (TSSOP-24) |
| EU-03KS | U4 | 1 | 3-position DIP switch for address select |
| 10kΩ | R6, R16, R17, R18 | 4 | Pull-up resistors (0805) |
| 4.7kΩ | R1, R4 | 2 | I2C pull-up resistors (0805) |
Pedalboard Coverage
| Modules | Pedals | Standard |
|---|---|---|
| 2 | 16 | Small portative / practice |
| 3 | 24 | European flat pedalboard |
| 4 | 32 | Full AGO specification |
| 4+ | 32+ | Extended range instruments |
Hall-Effect vs. Mechanical Switches
| Characteristic | Mechanical Switch | Hall-Effect Sensor |
|---|---|---|
| Lifespan | ~100,000 cycles | Unlimited (no contact) |
| Bounce | Requires debouncing | No bounce |
| Consistency | Degrades over time | Constant |
| Maintenance | Periodic replacement | None |
| Response time | Variable | Consistent |
Mounting
Small magnets (typically 3mm × 1mm disc magnets) are affixed to the underside of each pedal key. The sensor PCB is mounted on the pedalboard frame beneath the keys, positioned so that each magnet passes over its corresponding hall-effect sensor when the key is depressed.
Open Source
Full schematics, PCB layout, and BOM available on OSHWLab: