Hacking Pixmob Bands And Finding A Toolchain

The Pixmob band is an LED wrist strap, of the type often used at big concerts or other public events. Many have tinkered with the device, but as of yet, nobody was running custom code. It wouldn’t be easy, but [JinGen Lim] got down to work.

The wristbands are given out to concertgoers to create synchronized light shows in the crowd.

A teardown of a 2016 device revealed it consisted of an RGB LED, an IR sensor, a small EEPROM and a coin cell, which were all common parts. Unfortunately, the ABOV MC81F4204 microcontroller was a little more obscure. It’s a part that’s quite hard to find, and uses a proprietary programmer and an ancient IDE.

Searches online proved fruitless, and a working programmer remained outside [JinGen]’s grasp. Undeterred, he decided to simply walk into the company’s Korean headquarters and ask for help. As the part was end-of-life, they were unable to supply a programming device, but happily provided documentation for the chip that wasn’t publicly available. With this in hand, it was possible for [JinGen] to build his own programmer instead.

Booting up a copy of the ABOV IDE, with his newly-built programmer in hand, it was relatively easy to get the chip running custom code. Going the extra mile, [JinGen] even hacked the Arduino IDE to be partially compatible with the platform! A silicon error in the MC81F4204 design bricks the chips after only a few flash rewrites, so its never going to be the most useful platform, but it works nonetheless.

The Pixmob hardware has continued to evolve, and it’s unlikely modern units still use the same chip. Despite this, it’s a great example of what can be achieved by a little sleuthing and asking the right people the right questions. Others have attempted to hack similar products before, found at Disneyland and Coldplay concerts. You won’t catch this author at either, but if you’ve hacked something similar, be sure to reach out on the tip line!

 

13 thoughts on “Hacking Pixmob Bands And Finding A Toolchain

  1. Do they have some kind of spatial triangulation, so they can adress each pixmob separately based on it’s location. For example to make “waves” of light propagating through crowd? What technology do they use for this? Guess it’s not GPS.

    1. With IR, if you had speedy enough IR projector, you could project very precise patterns on crowd. Or small IR laser with galvo… With enough power for that ir blasters, could ruin most of smartphone recordings.

    2. They should use that trick the guy used on his Christmas tree – blink them one at a time, and register positions using a camera. Then you can “project” animation onto the crowd.
      May require periodic resyncing since people will be moving around a bit.

    3. They work by controlling the projection area of the IR command. Want everyone to flash blue? Beacon the “blue” command on the bright Omni IR transmitter. Want to paint a red stripe up the middle? Enable only the center column of pixels on your command projector, and project the “red” command. Sorry, no links – but I think I found this info just googling.

    1. “Actually visiting the headquarters is a whole new level of dedication.”

      Walking to South Korea to visit the company requires a “level of dedication” beyond most of us!
      B^)

      1. I would say it all depends on where you live and where your other travels take you. If you are in the area cause you live there or on other business, what the heck. It is no big deal. Now if you fly there from the US, just to show up on their doorstep to beg for documentation on an obsolete device, I would say you have mush for brains. But that is just me.

  2. “A silicon error in the MC81F4204 design bricks the chips after only a few flash rewrites…”

    This probably explains why a device from an obscure manufacturer was chosen to be used in a giveaway on-time use device. The pixmob designer probably got the entire production run for a token amount.

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