# XIAO ESP32-C6 Sensor Node

This Arduino sketch reads a BNO086 IMU and MAX-M10S GPS and publishes versioned, newline-delimited JSON over the Seeed RS485 expansion board. It produces vehicle telemetry only; Cargo remains the controller and `/api/v1` authority.

| Function | XIAO pin |
| --- | --- |
| RS485 DE / TX / RX | D2 / D4 / D5 |
| BNO086 SDA / SCL | D7 / D8 |
| GPS TX to XIAO RX | D9 |
| GPS RX from XIAO TX | D10 |

Power both sensors from 3.3V with shared ground. Required Arduino libraries are Adafruit BNO08x, TinyGPSPlus, and ArduinoJson 6.x. Enable **USB CDC On Boot** for diagnostics. GPS uses hardware UART0 at the verified 38400 baud; RS485 uses hardware UART1.

The BNO086 uses the verified `0x4B` I2C address on D7/D8. If initialization fails, verify 3.3V/GND, SDA/SCL wiring, and the breakout's PS0/PS1 configuration.
Firmware retries the fixed address during power-up and periodically retries afterward, so a slow BNO086 power-up does not require cycling the XIAO. If the BNO086 resets at runtime, rotation-vector reporting is enabled again automatically.

The node sends `sensor_status` at 115200 baud every 200 ms. See `docs/SENSOR_NODE_PROTOCOL.md`. The initial firmware is transmit-only; add a dashboard receiver after bench-testing the node, RS485 polarity, and sensor axes.

During bring-up, `USB_TELEMETRY_ENABLED` mirrors each RS485 JSON frame to the Arduino Serial Monitor at 115200 baud. Set it to `0` in `sensor_node_config.h` when continuous USB output is no longer wanted.