smart-serow/arduino/README.md

# Arduino

Sensor interface running on Arduino Nano, communicating with Pi via UART.

## Sketches

| Folder | Purpose |
|--------|---------|
| `main/` | Primary telemetry sketch |

## Current Capabilities

- Battery voltage monitoring (voltage divider on A0)
- WT61 IMU/gyro via AltSoftSerial (9-axis: accel, gyro, euler angles)
- Duplex UART to Pi at 115200 baud, 10Hz telemetry output
- Simple text-based protocol for easy debugging

## Dependencies

Install via Arduino Library Manager:
- **AltSoftSerial** by Paul Stoffregen - for WT61 IMU serial

## Pin Assignments

| Pin | Function |
|-----|----------|
| A0 | Battery voltage (via divider) |
| D0 (RX) | Pi UART RX ← Arduino TX |
| D1 (TX) | Pi UART TX → Arduino RX |
| D8 | WT61 IMU RX (AltSoftSerial) |
| D9 | WT61 IMU TX (unused, AltSoftSerial fixed pin) |
| D13 | Status LED (heartbeat) |

## Hardware

- **MCU**: Arduino Nano (ATmega328P)
- **Pi Connection**: UART at 115200 baud (TX→RX, RX→TX, common GND)
- **IMU**: WT61 module at 9600 baud, 20Hz output
- **Voltage sensing**: Resistor divider (100k/47k) scaled for 0-20V input

## Protocol

TSV (tab-separated), null-terminated frames at 10Hz. See [PROTOCOL.md](PROTOCOL.md) for full specification.

## Planned

- RPM sensing (pulse counting from ignition coil)
- Gear position indicator  
  
### Not planned

- Engine temperature (thermocouple/NTC)  
  *Borderline do not want to do, simple but not really useful*
- Turn signal / high beam status  
  *No need to do something the dash already does*