python backend arduino service

pi/backend/README.md

@@ -1,6 +1,6 @@
 # Backend
 
-Python GPS service for Smart Serow. Connects to `gpsd`, buffers positions, exposes HTTP API.
+Python GPS and Arduino telemetry service for Smart Serow. Connects to `gpsd` and Arduino serial, buffers data, exposes HTTP API.
 
 ## Setup
 
@@ -28,9 +28,11 @@ uv run flask --app main run --host 0.0.0.0 --port 5000 --reload
 
 | Endpoint | Description |
 |----------|-------------|
-| `GET /health` | Health check, shows gpsd connection status |
+| `GET /health` | Health check, shows gpsd and Arduino connection status |
 | `GET /gps` | Latest GPS fix (lat, lon, alt, speed, track) |
-| `GET /gps/history` | Last 100 buffered positions |
+| `GET /gps/history` | Last 100 buffered GPS positions |
+| `GET /arduino` | Latest Arduino telemetry (voltage, rpm, eng_temp, gear) |
+| `GET /arduino/history` | Last 100 buffered Arduino readings |
 
 ## Test from SSH
 
@@ -38,6 +40,8 @@ uv run flask --app main run --host 0.0.0.0 --port 5000 --reload
 curl http://localhost:5000/health
 curl http://localhost:5000/gps
 curl http://localhost:5000/gps/history | jq
+curl http://localhost:5000/arduino
+curl http://localhost:5000/arduino/history | jq
 ```
 
 ## gpsd Setup (Pi)
@@ -62,9 +66,48 @@ gpsmon
 cgps -s
 ```
 
+## Arduino Setup (Pi)
+
+The Arduino Nano connects via USB serial (typically `/dev/ttyUSB0` or `/dev/ttyACM0`).
+
+```bash
+# Check available ports
+ls /dev/tty*
+
+# May need dialout group for serial access
+sudo usermod -aG dialout $USER
+# Then log out and back in
+```
+
+### Arduino Protocol
+
+**Production format (JSON at 115200 baud):**
+```json
+{"v":12.45,"rpm":4500,"eng":85,"gear":3}
+```
+
+**Legacy text format (also supported):**
+```
+V_bat: 12.45V
+RPM: 4500
+ENG: 85C
+```
+
+The parser tries JSON first, falls back to regex for legacy format.
+
+### Configuring the Port
+
+Edit `main.py` to change the default port:
+```python
+arduino = ArduinoService(port="/dev/ttyACM0", baudrate=115200)
+```
+
 ## Stub Mode
 
-If `gpsdclient` isn't installed or gpsd isn't running, the service generates fake GPS data for UI testing.
+- **GPS**: If `gpsdclient` isn't installed or gpsd isn't running, generates fake GPS data
+- **Arduino**: If `pyserial` isn't installed or serial port unavailable, generates fake telemetry
+
+Both services run in stub mode for UI testing without hardware.
 
 ## Deploy