Hardware Wiring

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.