gps manipulations tailored to sim7600h hat

pi/backend/README.md

@@ -178,6 +178,19 @@ The Pi's internal pull-down (~50kΩ) will overpower high-value external resistor
 
 Physical switches/connectors need debouncing. Current implementation requires 15 consecutive identical readings (~750ms at 20Hz) before accepting a state change. Tune `required_consecutive` in `gpio_service.py` as needed.
 
+## Utilities
+
+Standalone tools live in `pi/utils/` (not part of the backend service):
+
+| Tool | Description |
+|------|-------------|
+| `at_terminal.py` | Interactive AT command terminal for SIM7600 (pyserial). Default port: `/dev/ttyUSB2` |
+
+```bash
+python pi/utils/at_terminal.py              # default /dev/ttyUSB2
+python pi/utils/at_terminal.py /dev/ttyUSB3 # specify port
+```
+
 ## Deploy
 
 TODO: Add to `scripts/deploy.py` as second target + systemd service.