Environmental Noise Meter (ESP32-C3 Slave + ESP32-S2/S3 Master)

This repository contains an I2C distributed noise monitoring setup:

• src/: ESP32-C3 firmware acting as I2C slave and acoustic processing node.
• examples/: ESP32-S2/ESP32-S3 firmware acting as I2C master/reader.

Features

• ADC sampling and DSP processing for acoustic indicators.
• I2C slave protocol compatible with current and legacy masters.
• Structured payload (SensorData) for robust host integration.
• Basic long-term indicators (Ld, Le, Ln, Lden) when device time is available.

Hardware Wiring

1) Sensor Node (ESP32-C3, I2C slave)

Signal	ESP32-C3 Pin
MIC OUT (MAX4466)	GPIO 4
I2C SDA	GPIO 8
I2C SCL	GPIO 10

2) Master Node

For ESP32-S2 default example mapping:

Signal	ESP32-S2 Pin
I2C SDA	GPIO 8
I2C SCL	GPIO 9

For XIAO ESP32-S3 default example mapping:

Signal	ESP32-S3 Pin
I2C SDA	GPIO 5
I2C SCL	GPIO 6

Important:

• Use common GND between boards.
• Use 3.3V logic.
• Add pull-up resistors (typically 4.7k to 3.3V on SDA/SCL) if your boards do not include them.

I2C Protocol

• Slave address: 0x08

Commands (1 byte):

Command	Value	Response
GET_STATUS	0x20	1 byte (1 mic OK, 0 mic error)
GET_STATUS legacy	0x00	Same as above (backward compatibility)
GET_DATA	0x01	Full SensorData struct
GET_DB legacy	0x10	4-byte float
GET_RAW_MV legacy	0x30	4-byte uint32
GET_LMAX legacy	0x40	4-byte float
GET_L10 legacy	0x60	4-byte float
GET_L90 legacy	0x70	4-byte float

Notes:

• Command 0x09 is reserved for identify response and also accepted as legacy "set time" when sent with 4 additional bytes.
• Master example polls every 5 seconds by default.

Build and Flash (PlatformIO)

Slave (ESP32-C3):

• Open repository root in VSCode/PlatformIO.
• Build/upload environment: lolin_c3_mini.

Master examples:

• Open examples/ in VSCode/PlatformIO.
• Build/upload environment: seeed_xiao_esp32s3 or lolin_s2_mini.

Calibration

• Constants in src/main.cpp: CALIBRATION_DB (e.g. 94.0), CALIBRATION_RMS_MV (measured with calibrator).
• Procedure and MAX4466 setup (wiring, potentiometer gain, ISO 1996-2 / Decreto 213/2012): docs/CALIBRACION.md.
• Calibration firmware (standalone, Serial output of RMS mV and LAeq): run the example in examples/calibration/ (env lolin_c3_mini), then use the stable RMS (mV) value as CALIBRATION_RMS_MV in the main firmware.

License

GPL-3.0. See LICENSE.