docs: add M9N GPS module plan

docs/HARDWARE.md

@@ -235,3 +235,7 @@ Important guardrails:
 - Confirm relay polarity/state behavior.
 - Confirm available GPIO for DS18B20 and any optional OLED/status hardware.
 - Treat the LilyGO board as the controller, not the high-current load path.
+
+## M9N GPS Module
+
+The dashboard enclosure will include an M9N GPS module connected to the ESP32-S3 dashboard over UART. It will provide GPS fix status, satellite count, position, speed, and UTC time. Future work will use GPS time/location for automatic timezone and DST handling.

docs/dashboard-esp32s3.md

@@ -291,3 +291,7 @@ Each temperature sensor supports optional high-temperature alerting:
 - `high_alert`
 
 When enabled and the live sensor temperature exceeds the configured threshold, the Cargo ESP includes `high_alert: true` for that sensor in `/api/v1/status`. The ESP32-S3 dashboard colors the affected grouped temperature tile red if any sensor in that displayed group is in alert.
+
+## M9N GPS Module
+
+The dashboard enclosure will include an M9N GPS module connected to the ESP32-S3 dashboard over UART. It will provide GPS fix status, satellite count, position, speed, and UTC time. Future work will use GPS time/location for automatic timezone and DST handling.

docs/gps-m9n.md

@@ -0,0 +1,52 @@
+# M9N GPS Module Plan
+
+## Role
+
+The M9N GPS module will live in the dashboard enclosure and provide:
+
+- GPS position
+- GPS speed
+- Satellite/fix status
+- UTC time
+- Future automatic timezone/DST support
+- Optional GPS fallback speed display
+
+## Location
+
+Preferred mounting location:
+
+- Inside the top dashboard enclosure
+- Under the windshield
+- Near the ESP32-S3 dashboard display
+
+This should provide a clean enough sky view for normal vehicle GPS use.
+
+## Wiring
+
+Planned connection to dashboard ESP32-S3:
+
+- GPS TX -> ESP32 UART RX
+- GPS RX -> ESP32 UART TX, optional
+- GPS VCC -> 3.3V or 5V depending on module board
+- GPS GND -> dashboard ground
+
+PPS is optional and not required for v1.
+
+## V1 Data Goals
+
+Initial GPS fields:
+
+- Fix valid
+- Satellite count
+- Latitude
+- Longitude
+- Speed
+- UTC time
+
+## Future Features
+
+- Automatic timezone lookup
+- Automatic DST handling
+- Trip logging
+- GPS-based speed fallback
+- GPS diagnostics screen

docs/project-state.md

@@ -358,3 +358,7 @@ Each temperature sensor supports optional high-temperature alerting:
 - `high_alert`
 
 When enabled and the live sensor temperature exceeds the configured threshold, the Cargo ESP includes `high_alert: true` for that sensor in `/api/v1/status`. The ESP32-S3 dashboard colors the affected grouped temperature tile red if any sensor in that displayed group is in alert.
+
+## M9N GPS Module
+
+The dashboard enclosure will include an M9N GPS module connected to the ESP32-S3 dashboard over UART. It will provide GPS fix status, satellite count, position, speed, and UTC time. Future work will use GPS time/location for automatic timezone and DST handling.

docs/roadmap.md

@@ -188,3 +188,7 @@ Next Dashboard Milestones:
 - OBD-II integration
 - CAN integration
 - BNO085/BNO086 off-road attitude display
+
+## M9N GPS Module
+
+The dashboard enclosure will include an M9N GPS module connected to the ESP32-S3 dashboard over UART. It will provide GPS fix status, satellite count, position, speed, and UTC time. Future work will use GPS time/location for automatic timezone and DST handling.