S.BUS Gamepad

Description

Ever wanted to use a FrSky Taranis wirelessly with PC simulators like FPVFreerider or RC-AirSim? This project will help you do so. The idea was to use a Teensy 2.0 USB controller and pair it with a FrSky XM receiver. The Teensy on one side will provide a USB HID gamepad to the host computer while on the other it will read the S.BUS protocol off the receiver using the Universal Asynchronous Receiver Transmitter (UART). To read the S.BUS signal an inverter in form of a simple transistor will be needed between the Teensy and the receiver. For more details please see the docs directory.

Update: If you would like to use an ExpressLRS receiver instead of the FrSky XM receiver then please check out these instructions.

Hardware

• Teensy 2.0
  • available here: PJRC, Teensy 2.0
• FrSky XM Receiver
  • available here: FrSky, XM Receiver
• A transistor & resistor to invert the S.BUS signal for the Teensy
  • available here: Reichelt, 2N7000, 10K Resistor

Software

• AVR 8-bit gcc toolchain
  • available here: Microchip, gcc toolchains
• HalfKey Loader teensy_loader_cli
  • available here: PJRC, teensy_loader_cli
• Dean Camera's excellent Lightweight USB Framework for AVRs (LUFA)
  • available here: Four Walled Cubicle, LUFA

Build

• clone or download the firmware
• edit the Makefile and change the LUFA_PATH to wherever you installed LUFA
• make sure the avr-gcc and teensy_loader_cli are in your path
• execute make to build the hex file
• press and release the tiny Teensy pushbutton to activate the HalfKey bootloader
• execute make teensy to download the hex file to the attached Teensy

If you don't want to build the software yourself just download the Gamepad.hex.teensy file and load it onto the Teensy using: teensy_loader_cli --mcu=atmega32u4 -w -v Gamepad.hex.teensy

Alternative Build

Here are a few tips for adjusting the build to an Arduino Micro (original or clone). You will need avrdude to program the Micro.

• edit the Makefile and change the BOARD variable from TEENSY to MICRO
• execute make avrdude AVRDUDE_PROGRAMMER=avr109 AVRDUDE_PORT=<serial port> to download the hex file to the attached Micro

Replace <serial port> with the device name the Micro is connected to on your computer after resetting. Depending on the bootloader installed on your Micro you might have to change AVRDUDE_PROGRAMMER value from avr109 to arduino. If you don't want to build the software yourself just download the Gamepad.hex.micro file and load it onto the Micro using: avrdude -p atmega32u4 -P <serial port> -c avr109 -U flash:w:Gamepad.hex.micro

Usage

Create a new model for the S.BUS gamepad on your transmitter. Make sure that you enable at least 4 channels (e.g. ailerons, elevator, throttle and rudder) for the receiver. Bind the receiver like you normally would. Use software like HTML5 Gamepad Tester to test the S.BUS gamepad. Once you have confirmed operation start your favorite simulator and enjoy.

Date: 2024-05-20