# Hardware Wiring

## Components (per node)

- ESP32 development board (38-pin DevKit, 19 pins per side)
- INMP441 I2S MEMS microphone circular module (14mm diameter)

## I2S Pin Mapping

| Mic Pin | ESP32 GPIO | Signal              |
|---------|------------|---------------------|
| VDD     | 3.3V       | Power               |
| GND     | GND        | Ground              |
| L/R     | GND        | Channel select (left) |
| WS      | GPIO 25    | Word Select (LRCLK) |
| SD      | GPIO 32    | Serial Data         |
| SCK     | GPIO 33    | Bit Clock           |

## Mic Module Layout

The INMP441 module is a 14mm circular board with a 2x3 pin header:

```
  GND   VDD   SD
   ●     ●     ●
  ( microphone  )
   ●     ●     ●
  LR    WS    SCK
```

- **Column pitch:** 2.54mm
- **Row separation:** 7.62mm
- L/R pin ties to GND for left channel selection

## Carrier PCB

The node carrier board (`pcb/soundspy-node.kicad_pcb`) mounts the ESP32 DevKit and the INMP441 module together in a 30×68mm board with a USB-C notch at the bottom for case passthrough. The PCB has a 3mm hole aligned with the mic's sound port.

KiCad symbol and footprint reference for the INMP441 module (legacy KiCad 4/5 format):
https://github.com/barafael/inmp441-breakout-kicad

See `pcb/mics/inmp441/DESIGN.md` for full pin specs and dimensions.

## Notes

- L/R tied to GND selects the left channel, matching `I2S_CHANNEL_FMT_ONLY_LEFT` in firmware.
- The firmware samples at 44.1 kHz, 32-bit, shifted right by 8 bits to recover the 24-bit value.
- ESP32 DevKit 3.3V rail is sufficient. Do not connect mic VDD to 5V.
- The carrier PCB has a 100nF decoupling cap (C1) on the 3V3 line near the mic connector.