shawn
0ae2ca6e8e
Custom I2S HAT for Pi Multi-FX Pedal — full hardware package: - KiCad project: schematic (kicad_sch), PCB layout (kicad_pcb), project file - Custom DT overlay: pcm1808-pcm5102-overlay.dts (no upstream overlay exists for PCM1808) - docs/hardware-bom.md: BOM (9.25 HAT + 1.75 with enclosure), wiring diagram, PCB design notes - docs/config-audio.md: DT overlay build, ALSA config, JACK integration, troubleshooting - scripts/install_hat.sh: One-command install + test suite (6 tests) - hardware/gerber/: JLCPCB fab instructions and assembly notes Circuit: Guitar input → TL072 preamp (gain ~20dB) → PCM1808 ADC → RPi I2S → PCM5102 DAC → RC filter → output jack I2S: BCLK/GPIO18, LRCLK/GPIO19, DIN/GPIO20, DOUT/GPIO21 Stacking header passes all 40 GPIO pins for footswitches/LEDs/display
96 lines
3.3 KiB
Markdown
96 lines
3.3 KiB
Markdown
# PCM1808+PCM5102 I2S HAT — JLCPCB Fabrication Package
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> This directory contains the fabrication files for the Pi Multi-FX Pedal I2S HAT.
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> Board dimensions: 65×56mm, 2-layer, 1.6mm FR4
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> Target fab: JLCPCB (but compatible with any PCB fab)
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---
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## Files
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| File | Description |
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|------|-------------|
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| `jlcpcb-bom.csv` | Bill of Materials for JLCPCB assembly |
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| `jlcpcb-cpl.csv` | Component placement / centroid file |
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| `fabrication-readme.md` | This file — fab notes and instructions |
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### Gerber Generation
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Gerber files must be exported from KiCad (not committed as generated binary files):
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```bash
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# Using KiCad 8.0 CLI:
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kicad-cli pcb export gerbers \
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--layers "F.Cu,B.Cu,F.Paste,B.Paste,F.SilkS,B.SilkS,F.Mask,B.Mask,Edge.Cuts" \
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--output hardware/gerber/ \
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hardware/pi-multifx-hat.kicad_pcb
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# Generate NC drill file:
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kicad-cli pcb export drill \
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--output hardware/gerber/ \
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hardware/pi-multifx-hat.kicad_pcb
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# Generate placement file for PCBA:
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kicad-cli pcb export position \
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--format csv \
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--units mm \
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--output hardware/gerber/jlcpcb-cpl.csv \
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hardware/pi-multifx-hat.kicad_pcb
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```
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### JLCPCB Order Specs
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| Parameter | Value |
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|-----------|-------|
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| **PCB Qty** | 5 (minimum) |
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| **PCB Layers** | 2 |
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| **PCB Thickness** | 1.6mm |
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| **PCB Material** | FR4 |
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| **PCB Color** | Green (ENIG for audio grade, HASL ok) |
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| **Surface Finish** | ENIG (gold) — preferred for audio signal integrity |
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| **PCB Dimensions** | 65×56mm |
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| **Min Track** | 0.254mm (10mil) |
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| **Min Hole** | 0.3mm |
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| **Impedance** | Not critical (audio frequencies) |
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| **PCBA** | Top side only (bottom is GND pour) |
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| **RoHS** | Yes |
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### Design Notes for Fab
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1. **Edge plating**: Request edge plating on mounting holes for EMI shielding (connect to GND)
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2. **Copper pour**: GND flood fill both layers — no thermal relief needed on audio circuit
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3. **Via tenting**: Tent all vias (prevents solder wicking during wave soldering)
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4. **Silkscreen reference designators**: Use JEDEC standard ref des (U1-U4, C1-C10, R1-R6, J1-J3)
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5. **Mounting holes**: 3.2mm non-plated through holes at 4 corners (standard 1590B footprint)
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6. **ENIG preferred over HASL**: Lower noise floor for audio circuits
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### PCBA (Assembled Board) Parts
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For JLCPCB assembly (PCBA service), the following parts must be in their extended/global parts catalog:
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| Part | JLCPCB Part? | Alternative |
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|------|:------------:|-------------|
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| PCM1808 (TSSOP-14) | Yes (C469019) | — |
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| PCM5102A (TSSOP-20) | Yes (C965928) | PCM5102APA |
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| TL072 (SOP-8) | Yes (C8290) | TL072CDR |
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| AMS1117-3.3 (SOT-223) | Yes (C6078) | — |
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| 0805 caps (100nF) | Yes (C52923) | — |
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| 0805 resistors | Yes | — |
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Components NOT in JLCPCB assembly catalog (must be hand-soldered or requested separately):
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- Electrolytic capacitors (10µF radial) — verify JLCPCB has SMD alternatives
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- 6.35mm audio jacks (panel-mount)
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- 2×20 female stacking header
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- M2.5 standoffs and screws
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### Case Fit
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The PCB is 65×56mm, designed to fit a **1590B diecast aluminum enclosure** (internal dimensions ~107×55×25mm usable). Mounting hole centers at 3.175mm from edges.
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### Test Points
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Consider adding test points on next revision:
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- TP1: 3.3V rail
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- TP2: 5V rail
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- TP3: Preamp output (before DC blocking cap)
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- TP4: PCM1808 DOUT (verify I2S data with scope) |