I recently went to a concert that used RF based PixMob wristbands. These are given to the attendees, and allow light effects to play across the entire arena, with each person being a single RGB pixel. Very cool effect in my opinion.
We were told multiple times that the wristbands are assigned to each seat, and would not know if you moved. This is different than the IR based ones used in Taylor Swift’s recent tour for example. RF wristbands are controlled from a central location, with a single “shoebox sized” transmitter (from PixMob website). IR wristbands are controlled through focused IR beams blasted from above, allowing specific areas to be hit and light up. So IR bands don’t care if you move or not.
Since the RF ones are assigned to a seat, and are receive only, they very likely have a unique ID held inside each one. A calibration procedure, where a camera is pointed down at the arena after placing the bands at each seat, would learn the location of the bands and store those locations in a database with the unique IDs. This process likely works similar to the Twinkly light string calibration process, where all of the lights are precisely flickered on and off based on their IDs, and the video from the camera above is used to see which pixels are on when certain IDs are told to light up.
In my attempts to get the wristband to light up again, here is what I’ve found. I have not yet successfully lit the LEDs via radio control, but will definitely post again if I’m successful.
For the CEMENT V1.1 PixMob circuit:
RF Frequency in use is 915 Mhz, based on the 26.1522 MHz crystal on board.
Radio IC is a CMT2210LH receiver, using OOK demodulation
SOT23-5 chip marked AK19T is likely an I2C EEPROM
Unmarked chip is a microcontroller, directly driving the LEDs with pins 5,6,7
My next step is to attempt reading from the EEPROM to determine the unique ID, then I will try sending commands that include it to see what happens.
EDIT: Found this awesome github of reverse engineering efforts, including several RF recordings from concerts! I’ve successfully used the recorded codes from here to get my RF wristband to light up.
Will follow up later with another post and possibly a full project.