USB joystick adapter for RC receivers with PWM output. It can be used for VRC Pro or other simulators. Tested on Fedora Linux and Steam Deck.
This is heavily based on the excellent work of Nicholas Regitz: https://kekse23.de/2017.02.22/778/diy-rc-usb-adapter-fuer-vrc-pro/
In comparison with the original code the following changes were made:
- Initial auto calibration support,
- EEPROM storage of the calibration,
- code refactor, joystick events are now sent at once, not individually for each axis, which may improve real-time performance.
Wire the dongle to the RC receiver which is paired with the transmitter.
For cars the channel 1 is usually steering, channel 2 is throttle/break. Channel 2 is usually also used for powering of the receiver.
For aircrafts/drones the mapping is usually AETR (Aileron, Elevator, Throttle, Rudder), i.e. the channel 1 is usually roll, channel 2 pitch, channel 3 throttle, and channel 4 yaw.
Connect the dongle to the USB port. Shortly, after the connection to the USB port the TX LED (usually the blue LED), will start blinking fast. Then you have cca. 10 seconds for moving of all channel controls through the limit positions (calibration). When the LED stops blinking the joystick will start function normally. If you did the calibration, it is saved to the EEPROM.
If you didn't touch the controls during the 10 seconds calibration interval, the calibration is restored from the EEPROM.
So the typical usage is:
- connect the dongle to the USB port, wait cca. 14 seconds (4 + 10) until the blue LED stops blinking, enjoy your game
- if you want to (re)calibrate, (re)plug the dongle to the USB port, wait cca. 4 seconds until the blue LED starts blinking fast, then you have cca. 10 seconds interval for calibration, move the controls of the channels you are interested in through the limit positions. After 10 seconds, the LED stops blinking and the calibration is saved to the EEPROM, enjoy your game.
I used Arduino Pro Micro from Aliexpress, the 3.3 V / 16 MHz version with the ATmega 32U4. It seems there are two versions, 3.3 V and 5 V. Both versions works. For the 3.3 V version you need to close (solder bridge) the J1 jumper (near the USB connector and the TX0 pin). It will bypass the 3.3 V internal regulator and it will run on the 5V directly from the USB port. For the 5 V version bypassing the regulator is optional, but recommended, because you will get 5 V instead of the cca. 4.8 V due to the voltage drop on the internal regulator.
Channels wiring for the Arduino Pro Micro board from Aliexpress:
| PCB marking | ATmega 32U4 marking | Channel |
|---|---|---|
| 3 | PD0 | 1 |
| 2 | PD1 | 2 |
| RXI | PD2 | 4 |
| TX0 | PD3 | 3 |
Connect VCC and GND only for the channel 2. For the rest of channels leave it unconnected. I guess this is to lower signal noise floor and to prevent possible shorts if the receiver is really badly wired (normally, reversing the servo connector is safe, because VCC is in the middle and PWM output can usually withstand 5V/GND without problem).
For some reason currently unknown to me, the Arduino boards have the port D marked differently from the datasheet, so I used the wiring table above.
Good 3D printed case design: https://www.thingiverse.com/thing:4543077
It seems it's designed for the 33 mm long boards, which are probably boards with the USB micro connector. I used board with the USB-C connector which is 35 mm long, so I had to enlarge the longer side of the case by 2.6 mm for a perfect fit.
It's probably for 2 channels dongles, to accomodate wires for 4 channels I had to enlarge the height of both lids 0.5 mm each, i.e. the 1 mm total enlargement. I also had to file a cable hole a bit for 4 channels to fit.
Finally I drilled two mini holes (1 mm) for the RX/TX LEDs.
It would be better to modify the 3D design, but unfortunately, there is only STL file available and I didn't have a time to mod it or redesign it from the scratch.
You will need the Joystick library from the: https://github.com/MHeironimus/ArduinoJoystickLibrary
Put it to your Arduino libraries directory.
In the project set the board to "Arduino Micro".
Jaroslav Škarvada jskarvad@redhat.com 2025/04/20, refactor, added auto calibration, EEPROM support
kekse23.de RCUSB4 v1.1 Copyright (c) 2020, Nicholas Regitz
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