FPV UART Setup on Any Flight Controller
The rule that saves hours
Props off. Verify the exact flight-controller pinout. Never guess a power pad.
1. What a UART is
A UART is a numbered pair of transmit and receive pads. T1/R1 or TX1/RX1 is UART1; T3/R3 is UART3. TX transmits and RX receives, so signal wires cross. Ground is shared and peripheral power must match its required voltage.
2. Make a port map before soldering
| Example | Device | Wiring | Ports job |
|---|---|---|---|
| UART1 | ELRS | TX↔RX pair | Serial RX |
| UART2 | GPS | GPS TX→FC RX | Sensor: GPS |
| UART3 | Digital VTX | TX↔RX | MSP/DisplayPort |
| UART4 | Analog VTX | FC TX→control | SmartAudio/Tramp |
3. Betaflight Ports tab
Use the row matching the pads you wired. Configure ports first, Save and Reboot, then enable the matching feature elsewhere.
4. ExpressLRS example
- Ports: Serial RX on the connected UART.
- Receiver: Serial (via UART), provider CRSF.
- Telemetry enabled; RSSI ADC disabled.
serialrx_inverted = OFFserialrx_halfduplex = OFF
5. GPS, VTX and telemetry
GPS
GPS TX to FC RX is the minimum. Select GPS under Sensor Input and enable GPS. AUTO baud is a good starting point.
SmartAudio / Tramp
Normally FC TX goes to the VTX control wire. Select the correct protocol under Peripherals, then configure the VTX table.
Digital video OSD
HD systems commonly use MSP plus DisplayPort. Follow the exact air-unit and FC documentation.
6. Troubleshooting
- Bound but no receiver movement: check crossed wires, UART row, CRSF provider and uninverted pads.
- GPS icon stays off: verify GPS TX reaches the selected FC RX, GPS Sensor Input and feature are enabled, then test outdoors.
- Settings reset: remove conflicting assignments, especially MSP plus Serial RX.
- Device powers but has no data: power proves only power—recheck signal pads and ground.
- No spare UART: reserve SoftSerial for low-bandwidth uses.
Final bench test
- Props off and inspect soldering.
- Reopen Ports after Save and Reboot.
- Verify receiver channels and failsafe.
- Verify GPS outdoors.
- Verify OSD and VTX control with antenna installed.
- Power-cycle USB and battery separately.
Official references
Betaflight Ports Tab · Serial Guide · ELRS Wiring
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