Hardware Specification: Nodes

Target Hardware: Seeed Studio XIAO ESP32-S3 Role: Audio Playback, Light Sync, and Network Telemetry Node Total Units: 16

1. Pinout Mapping (The "Split-Brain" Layout)

This layout segregates the SPI Storage bus (Right Side) from the I2S/Action bus (Left Side) to minimize interference and simplify wiring.

Component	Function	XIAO Pin	ESP32 GPIO	Direction	Connection / Notes
Audio Amp	I2S Bit Clock (BCLK)	D0	1	Output	To MAX98357A BCLK
Audio Amp	I2S Word Select (LRC)	D1	2	Output	To MAX98357A LRC
Audio Amp	I2S Data (DIN)	D2	3	Output	To MAX98357A DIN
NeoPixel	LED Data	D3	4	Output	To WS2812B DIN (via 470Ω Resistor)
Battery	Voltage Sense	D4	5	Input (ADC)	Center of Voltage Divider (100kΩ / 100kΩ)
Button	Rescue / Config	D5	6	Input	Tactile Button to GND (Internal Pullup)
Status LED	Diagnostic Light	D6	43	Output	Red LED via 220Ω Resistor to GND
SD Card	Chip Select (CS)	D7	44	Output	To SD Module CS
SD Card	SPI Clock (SCK)	D8	7	Output	To SD Module SCK
SD Card	SPI MISO	D9	8	Input	To SD Module MISO
SD Card	SPI MOSI	D10	9	Output	To SD Module MOSI

2. Component Wiring Details

A. Power Architecture

• Battery: 3.7V LiPo connected to BAT+ / BAT- pads on the underside of the XIAO.
• Charging: Handled natively via the XIAO USB-C port.
• 5V Rail: The 5V pin on the XIAO header acts as the main power rail for peripherals (Outputs Battery Voltage when on battery, 5V when on USB).

B. Audio (MAX98357A)

• VCC: Connect to XIAO 5V pin.
• GND: Connect to Common GND.
• GAIN: Leave Floating (9dB) or connect to GND via 100kΩ resistor (12dB).
• SD_MODE: Connect to VCC via 100kΩ resistor (Force ON).

C. NeoPixels (WS2812B)

• VCC: Connect to BAT+ pad (or XIAO 5V pin). Do not power from 3V3.
• GND: Common GND.
• Data: D3 (GPIO 4).
• Note: If flickering occurs on battery power, add a 1N4001 diode in series with the NeoPixel VCC to drop the voltage slightly for logic level compatibility.

D. Inputs & Safety

• Rescue Button (D5): Must use INPUT_PULLUP in code. Logic: LOW = Pressed.
• Battery Monitor (D4):
  • Circuit: Voltage Divider.
  • R1: 100kΩ (Between BAT+ and D4).
  • R2: 100kΩ (Between D4 and GND).
  • Math: Voltage = (AnalogRead * 3.3 / 4095) * 2.

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3. Firmware Configuration Block

Copy and paste this block into the config.h or main.cpp file for the Agent.

// ==========================================
// HARDWARE PIN DEFINITIONS (XIAO ESP32-S3)
// Architecture: Split-Brain (SPI Right, I2S Left)
// ==========================================

// --- STORAGE (SD Card via SPI) ---
#define SD_CS_PIN       44  // D7
#define SD_SCK_PIN      7   // D8
#define SD_MISO_PIN     8   // D9
#define SD_MOSI_PIN     9   // D10

// --- AUDIO (MAX98357A via I2S) ---
#define I2S_BCLK_PIN    1   // D0
#define I2S_LRC_PIN     2   // D1
#define I2S_DIN_PIN     3   // D2

// --- VISUALS (WS2812B) ---
#define LED_PIN         4   // D3
#define NUM_LEDS        16  // Update with actual count

// --- UTILITIES ---
#define BAT_SENSE_PIN   5   // D4 (100k/100k Divider)
#define RESCUE_BTN_PIN  6   // D5 (Active LOW)
#define STATUS_LED_PIN  43  // D6 (Active HIGH)

// --- CONFIGURATION CONSTANTS ---
#define RESCUE_HOLD_TIME_MS 3000  // Hold button 3s to enter AP Mode
#define BATTERY_CALIBRATION 2.0   // Multiplier for voltage divider