TxTroller

TxTroller

A Radio Receiver-to-USB HID Gamepad Adapter.

Build Photos

Demo Video

Click to open in YouTube

What is this?

This is a simple adapter that will allow older-style Radio transmitter / receiver combos to be used as video-game controllers using the USB HID Gamepad device class.

Watch me crash quads using TxTroller: youtube video link

Hardware

For the initial stages, this is being developed for the Radiolink R8EF receiver, which is an 8-channel receiver operating on the 2.4GHz frequency band.

As for the transmitter that will be the actual gamepad, It will be the Radiolink T8FB transmitter, which is a 2.4GHz 8 Channels RC Remote Transmitter.

The microcontroller that will be responsible for translating the SBUS signals from the receiver to the USB device class is the XIAO RP2040 due to it's small footprint and easy-to-use C/C++ SDK.

PCB

The PCB has been designed using KiCAD 9.0. It is a 2 layer PCB with both top and bottom having thick signal traces and a ground fill.

PCB Schematics:

PCB layout:

PCB Preview:

3D Case

The case has been designed in Fusion 360, with the .f3z available in the /CAD directory, along with the exported .step files of the top and bottom parts of the case in /CAD/exports.

The case looks like this:

The case has side extrusions for friction-fitting the top and bottom part of the case together.

Firmware

Originally modified from raspberrypi/pico-examples/tree/master/usb/device/dev_hid_composite .

Checkout the Firmware directory to view more information on button mappings, firmware compiling / flashing and testing the data received from the receiver.

Ordering, BOM & 3d Printing

The PCB contains no SMD components or any other component that cannot be soldered using a normal soldering iron, hence no PCBA is required.

The PCB gerber .zip file is available in PCB/exports/.

BOM Table

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Note that the PCB states 150ohm resistor but we have only added 100ohm, this is because we can arrange 3 100 ohm resistors in such a way that the effective resistance becomes 150ohms (2parallel+1series).

As for the 3d prints, the following files need to be printed separately:

• CAD/exports/TxTroller_lid.step
• CAD/exports/TxTroller_bottom.step

Since they are designed to be friction fitted, no screws or heatset-inserts are needed.

Assembly Instructions

1. Get the PCB manufactured via any PCB fab (I used lioncircuits.com/)
2. Solder the transistor, LED, resistors, headers and then finally the MCU. (This order is preferred so as to not let other components get damaged due to less space)
3. Flash the firmware, connect your receiver and test whether the device is working fine.
4. Get the case 3d printed, set the PCB inside the bottom part of the case, close it via the lid.
5. If the case is loose, use a rubber band to firmly hold it in place. Connect the receiver and place it beneath the bottom part of the case.
6. Again use something like a rubber badn to hold the receiver firmly in place.
7. Build finished!

Credits

• https://github.com/controllercustom/dinput_tinyusb
• https://www.thingiverse.com/thing:6989033
• https://www.reddit.com/r/embedded/comments/1m6d1ei/gamepad_using_tinyusb_on_raspberry_pi_pico/
• https://github.com/gdsports/gamepad_tinyusb
• https://github.com/raspberrypi/pico-examples/tree/master/usb/device/dev_hid_composite

Thank You! 😼💖