Connecting an RC Receiver on Linux

This topic shows how to setup a PX4 Linux-based autopilot to connect and use a supported RC receiver on any serial port.

For RC types other than S.Bus, you can just connect the receiver directly to the serial ports, or to USB via a USB to TTY serial cable (e.g. like PL2302 USB to Serial TTL converter).

:::note For an S.Bus receiver (or encoder - e.g. from Futaba, RadioLink, etc.) you will usually need to connect the receiver and device via a signal inverter circuit, but otherwise the setup is the same. :::

Then Start the PX4 RC Driver on the device, as shown below.

Starting the Driver

To start the RC driver on a particular UART (e.g. in this case /dev/ttyS2):

rc_input start -d /dev/ttyS2

For other driver usage information see: rc_input.

Signal Inverter Circuit (S.Bus only)

S.Bus is an inverted UART communication signal.

While some serial ports/flight controllers can read an inverted UART signal, most require a signal inverter circuit between the receiver and serial port to un-invert the signal.

:::tip This circuit is also required to read S.Bus remote control signals through the serial port or USB-to-TTY serial converter. :::

This section shows how to create an appropriate circuit.

Required Components

• 1x NPN transistor (e.g. NPN S9014 TO92)

• 1x 10K resistor

• 1x 1K resistor

:::note Any type/model of transistor can be used because the current drain is very low. :::

Circuit Diagram/Connections

Connect the components as described below (and shown in the circuit diagram):

• S.Bus signal → 1K resistor → NPN transistor base

• NPN transistor emit → GND

• 3.3VCC → 10K resistor → NPN transistor collection → USB-to-TTY rxd

• 5.0VCC → S.Bus VCC

• GND → S.Bus GND

Signal inverter circuit diagram

The image below shows the connections on a breadboard.

Signal inverter breadboard