OpenPuck

OpenPuck

Opensource firmware for NRF52840 Pro Micro that copycats the Steam Controller 2 Puck and adds an Xbox and Switch mode.

[!WARNING] Every part of this project HEAVILY used LLMs. Everything from discovery of the protocol to writing the arduino sketch and running various automated benchmarks invovled Claude and Codex. This readme is the only organic, single origin, ethically sourced and humanely slaughtered assemblage of words in this project. I have done my best to review the code and I invite anyone concerned about the stability or security of this project to do the same.*

The Steam Controller 2

Released in 2026, the Steam Controller 2 represents the peak (IMO) of controller design. Trackpads, gyro, 4 back buttons, all with the flexibility of Steam Input brings the amazing flexiblity of the Steam Deck's controls to gaming PCs in general.

The "puck" is what the controller uses for wireless communication with the host device. It can handle 4 controllers paired to it at the same time and can run at a very low latency with all 4 connected. While the controller has a bluetooth mode too it has over twice the latency so the puck is truly where it's at.

The Problem

There are two fundamental problems with the controller:

1. The puck is not (yet) available for purchase separately from the controller so if you want a replacement or a second one (a single controller can pair to two) you're out of luck.

2. Steam Input isn't just a nicety, it's a requirement. This means that the controller is basically useless unless you have Steam running (outside of certain contexts that I personally consider niche). If, for example, you have gamepass and want to play FH6 through Gamepass you're gonna be in for a bad time and you'll probalby need specialized software running on your computer in order to make the controller work with it.

What this project does

Video Intro

OpenPuck uses a Pro Micro NRF52840 ($8 on Amazon, possibly cheaper elsewhere) which uses a radio similar to the one being used by the controller and the puck. Once the arduino sketch is uploaded it emulates the puck over USB to Steam by default and allows pairing the controller normally (almost, the lizard mode for when Steam is off might not be 1:1). Latency has been measured to be within 1ms of the official puck.

At any point you can hold all 4 back buttons and press X to switch over to *Xbox mode which maps all canonical inputs to their expected counterparts (plus L4 -> LB, L5 -> L3, etc which are configurable). In this mode the right trackpad acts as a mouse but at present this only works in Android and SteamOS.

Similarly you can hold all 4 back buttons and press Y to switch (teehee) over to a Switch mode. This emulates a pro controller full with gyro and haptics. There's other modes as well:

Button combo (configurable)	Mode	Comment
back-4 + A	Steam	Steam Controller Mode
back-4 + B	Lizard	Lizard mode, even if Steam is open
back-4 + X	Xbox	Xbox 360 Controller
back-4 + Y	Swith Pro	Switch Controller + Gyro + Haptics
WebUSB panel → mode 4	Hori Pad	Switch mode with no gyro or haptics
WebUSB panel → mode 5	DualSense + Gyro + Trackpad	PC only
WebUSB panel → mode 6	DS4/HIDGYRO + Gyro + Trackpad	PC only

I'm also adding various QOL items as I go as well. For example having to hold the Steam button for like 6 seconds feels like an eternity. If Steam is open you can do Steam +Y for a shutdown. I'm adding Steam + Y for 2 seconds as a shutdown chort in ALL modes now.

Note: to use the Switch mode on a real Switch you'll need to enable the pro controller wired communication option.

A note on the Lizard mode:

The Lizard mode behaves similarly to how the controller behaves when Steam is closed, but this will work even when Steam is open. This has a few advantages the biggest one being that you can use inputs when a high privilege application is in the foreground (like the Task Manager, when using Steam if you wanna be able to do that Steam must be run as admin).

Additionally it has some shortcuts that might be useful: Steam + L5/R5 will do volume control, RB is Alt so you can RB + Select to move through windows, LB is Ctrl and Steam + L4 ls Ctrl + Alt + Delete.

How to install/use it

You will need to flash OpenPuck.ino onto a compatible microcontroller. See build instructions document for more details.

Pairing

Both OpenPuck and the controller need to be hooked up to the same machine with a data capable USB C cable at the same time and Steam must be running. Steam should in most cases automatically pop up a menu to pair the controller. If not, you can go to Settings -> Controllers and press "Add Controller".

If you want to use the second slot for OpenPuck, you'll need to first turn the controller off and then hold LB + A + Steam to turn the controller back on (the chime when the controller comes on in this mode sounds different). Then connect the USB C cable and continue to pair.

Switching slots requires turning the controller off (Steam + Y if steam is running, Steam + Y held for 2 seconds if Steam isn't running or if you're in a different mode, or just hold the Steam button for an eternity until the controller shuts off) and then you hold RB for slot 1 and LB for slot 2 while holding A and Steam to turn the controller back on.

Configuration

A webusb based configuration UI is available here. It allows Switching the mode manually and changing the back button mapping for other modes among other things. This will likely only work in Chrome and Edge and needs the pro micro to be connected via USB to the same computer for it to function. Note that it might not work in all modes on all machines but should always work in the Steam Controller mode (which you can revert to with back-4 + A).

3D Printed Cases

• jaki-gh has contributed a 3D printable housing with OpenPuck written on it alongside a Steam logo. You can find that here.
• StonnedModder built a case meant to accomodate a USB C to USB A adapter which you can find here.
• Another plain case for these pro micros can be found here.

Future work

• Find a way to make Xinput mode and mouse work together on all platforms
• Multi-controller support is now working in Steam/Lizard mode (up to 4 controllers, see the U CDC command for a per-slot status dump). Non-puck modes (Xbox, Switch, PS5, DS4) remain single-controller by design — the user can pair one controller and use the appropriate mode.
• Design the charging portion (and make it short proof)

Contributions

The firmware is split into small, single-responsibility modules under OpenPuck/ (one file per emulated controller, plus the RF, config, and host-interface layers). Start with ARCHITECTURE.md for the map of how it all fits together and how to add a new USB personality.

I have tested this software fairly extensively but I have limited resources. I only have one controller so I've been unable to do full end-to-end multi-controller hardware testing — the per-slot session address, per-slot USB fanout, and per-slot haptic demux are in place and the design is sound, but the U CDC command exists specifically so anyone with a second controller can verify the per-slot state at a glance. Please submit issues with any issues you find. PRs also welcome of course.

Acknowledgements

• Valve for putting out the amazing controller
• Whoever wrote the drivers for SDL / Linux
• Alan for not scalping and selling me this controller for $120
• https://github.com/knflrpn/2wiCC for the Switch Pro controller mode help
• Massive thanks to u/Careful_Tune4744 for latency testing as well as testing and giving feedback on the Switch Pro mode
• Thanks to Lawstorant from a mutual discord server for constructive criticism of the repo's state

* Another note on LLM use

I want nothing more than for there to be a fully human coded alternative to OpenPuck that's on par with or better in every way. I would love to stop working on OpenPuck.

If someone builds an alternative that matches this criteria I would happily change the name of this project and archive this repo.