Saturday 20 May 2023

Smart Port Telemetry, INAV and F4

FrSKY receivers with S-Port capability can send telemetry data back to the transmitter. The data can come from FrSKY S-Port telemetry sensors but also from flight control boards (FCBs).

SBUS and Smart Port are inverted signals, compared to normal convention for flight control boards and receivers. Flight control boards need to un-invert these inputs to be usable.

F7 boards have inverters on all UARTs which can be enabled in the configurator, so SBUS and SmartPort inputs can be connected to any UART.

F4 boards only have one UART inverter (for SBUS), usually on the Rx2 pin. But we need an inverted Tx pin for the Smart Port input.

So this is where Soft Serial comes in. Soft Serial creates a software defined UART which can be inverted.

By enabling Soft Serial or "CPU based serial ports" Tx2 becomes available as an inverted pin for Smart Port connection.

The steps below show how:

1. Enable "Enable CPU based serial ports" and "Telemetry output" in the INAV configuration page

2. Choose "SmartPort" in the Telemetry column for SOFTSERIAL1 in the Ports page

3. Choose SBUS, OFF, AUTO or OFF in the Receiver page

4. On the F4 board connect SBUS to the SBUS pin and SmartPort into the TX2 pin

5. "Discover new" sensors on your transmitter, and you should see all the extra FC telemetry appearing.

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