Single-Layer PCB Design for PICO
0:59
Evaluating system specifications.
A split-board guitar instrument with an external drum/control surface, an internal compute/audio core built around PICO plus a Raspberry Pi 4 Model B 4GB, optional distributed comms via a CAN Bus HAT, balanced audio through an XLR Connector, and power from a 1S Li-ion Battery Pack.
Board Partition Board 1 - External control boardDiagram
Table
| Function | Lives here | Notes |
|---|---|---|
| Drum sequencer controls | Yes | Active mainly in drum-edit mode |
| Capacitive touch modules | Yes | Keep local to reduce noise pickup |
| UI LEDs | Yes | Keep with user controls |
| Audio circuitry | No | Keep off this board |
| Main processing | No | No Raspberry Pi 4 Model B 4GB here |
Table
| Function | Lives here | Notes |
|---|---|---|
| PICO | Yes | Real-time control coprocessor |
| Raspberry Pi 4 Model B 4GB | Yes | Main synth, storage, sequencing, UI state |
| CAN Bus HAT | Yes | Attach on the Pi side |
| Power conversion | Yes | Battery, charge, 5 V, 3.3 V |
| Audio output stage | Yes | Keep close to XLR Connector |
| Rotary encoder with push | Wired here | Direct to PICO |
Table
| Signal Group | Qty | Notes |
|---|---|---|
| 3.3 V | 1 | Logic power |
| GND | 2 | Use at least two returns |
| SDA / SCL or equivalent control bus | 2 | Preferred if modules support it |
| Interrupt / attention | 1 | Optional but useful |
| LED power or spare GPIO | 1-2 | Optional |
Table
| Block | Recommendation |
|---|---|
| Audio source | Software/audio engine on Raspberry Pi 4 Model B 4GB |
| Output conditioning | Dedicated analog/balanced driver stage |
| Connector | XLR Connector on core board edge |
| Placement | Keep close to analog stage, far from touch/control routing |
Recommended rails
| Rail | Source | Powers |
|---|---|---|
| Battery | 1S Li-ion Battery Pack | Raw energy source |
| 5 V | Boost/regulation from battery path | Raspberry Pi 4 Model B 4GB, CAN Bus HAT, audio support as needed |
| 3.3 V | Regulated logic rail | PICO, control board logic, sensors/modules |
Functional Modes
| Mode | Active Elements |
|---|---|
| Boot | PICO alive first if possible, Pi starting |
| Drum edit | External control board + PICO + Pi sequencer logic |
| Synth/play mode | Pi audio engine + rotary control + selected UI |
| CAN mode | Pi + CAN Bus HAT + external node comms |
| Storage access | Pi-local storage only |
Key Design Decisions
| Decision | Why |
|---|---|
| Keep touch controls on a separate exterior board | Better isolation and simpler mechanics |
| Put rotary control on PICO | Better real-time handling |
| Let Pi own storage | Eliminates unnecessary third storage board |
| Keep audio and XLR Connector on core board | Better analog integrity |
| Keep CAN on Pi side | Simplifies system ownership |
Main Risks
| Risk | Why it matters |
|---|---|
| 5 V power integrity | Pi stability depends on it |
| Ground noise into XLR path | Can ruin output quality |
| Long noisy control runs | Can hurt touch reliability |
| Too many raw inter-board signals | Makes wiring fragile and noisy |
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