Attempting to decode RF PixMob wristband (Cement v1.1 Waveband)

electronicsknowledge, future

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.

Stay tuned!

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.

Future: Remote Control Roomba Cam over WiFi!


Currently in the works… A remote control Roomba, with a pan/tilt camera mount and possibly a simple arm to hit handicapped buttons (to enter doors). Project goal: Use websocket protocol to communicate between a computer and Arduino microcontroller, using an Android phone as the USB/WiFi link.

Using javascript on an HTML page, the computer will send out commands depending on keys pressed on keyboard. The Android phone will take these commands and send them through USB On The Go (OTG) to the Arduino, which will finally control the Roomba through its serial port.  The Arduino can also connect to pretty much anything else, such as lights, motors, or sensors. The video feed is simply IP Camera app running on the Android phone in the background. Nothing super new here, but a fun challenge for me to get my feet wet in internet connectivity. 🙂 Stay tuned! I hope to be done before April 2016