“Hacking the PixMob infrared protocol to enable control of PixMob wristbands at home.
PixMob bracelets are LED wristbands distributed to every member of the audience at large events which all light up in sync to create massive, distributed light shows. The wristbands react to infrared commands from various types of fixed and moving transmitters. The wristbands have been used by various sports teams (including during the Super Bowl) and touring bands such as Coldplay, Shawn Mendes, Taylor Swift, Bad Bunny, The Weeknd, and Lady Gaga, to produce light shows that take advantage of the line-of-sight nature of IR light/”signals” to make light effects that vary by physical location in an event venue. After the event, bracelets are sometimes collected for reuse/recycling, but often attendees are left to take home the inactive bracelets.
Some prior work has been done to “reactivate” the PixMob bracelets after the conclusion of the event they were used in, to limited levels of success. Certain old models of PixMob bracelets can be put into a permanent motion-sensitive mode by soldering or unsoldering a pad on the PCB, but this doesn’t allow the bracelet to be controlled in sync with other bracelets wirelessly. Another project was able to upload custom firmware onto a PixMob bracelet board, but this requires taking apart the bracelet and having specialized equipment, and no IR-controlled lighting custom firmware has been released. One person has posted a video online wherein they demonstrate being able to turn their bracelet a couple different colors by pressing buttons on a TV remote (coincidentally generating “valid” codes), but the make and model of the TV remote were not specified and (as far as I’m aware) no reports of reproduction have been made.
This project set out to actually reverse-engineer the production PixMob bracelet IR protocol so that PixMob devices can be controlled via IR at home, just as they are during an event.
Hardware Notes:
We tested with six different versions of PixMob bracelets manufactured between 2014 and 2021 from various events including Portland Trail Blazers games, Superbowl LIV, and concerts of Taylor Swift, Coldplay, and The Weeknd. Each bracelet has an IR receiver and RGB LEDs along with pseudo random number generation capabilities and persistent memory. Some models also contain a motion sensor for motion-activated effects. Feel free to open an issue if you want more specific hardware information or teardown photos. A public FCC filing for one of the models of IR transmitters used at PixMob-equipped events confirms that they work on 940nm infrared light. There is some evidence that the bracelets enter a sleep mode when not in use for a while.
Methods:
A Flipper Zero device was used at a Coldplay “Music of the Spheres” concert and a Weeknd “After Hours Til Dawn” concert to record some of the IR commands sent to the PixMob bracelets worn by the audience. The Flipper device was then later used to re-transmit each of the recorded signals to PixMob bracelets of various generations, and their reactions were observed. Of over 100 recorded signals, only 3 caused immediate responses on the PixMob bracelets outside of the event. It is inferred that the majority of the codes are used to transmit “programming” information to the bracelets, to inform how they will react to late cue signals.”