Pixmob Smart Lightup Bracelet Teardown

I recently had the chance to attend game 1 of the NBA finals in Oakland's Oracle Arena.
It was an amazing experience that landed me an all access pass to the Arena for games 1 and 2. The purpose of my visit was to test out my day job's product in the environment. Being that the product involves RF communication, it was a complete flustercluck of frequency chaos. I arrived early and got a chance to meet with the NBAs contractor for 'RF Coordination'. The head honcho explained to us how they try to regulate all the frequencies in the arena so people can freely communicate as they need. This includes event staff, ESPN folk, food people, ushers, and anyone else with a walkie. He mentioned that the 2.4 GHz and 5 GHz ranges were free range since they are near impossible to regulate, which makes sense. He also mentioned that reps from companies like ATT and T-Mobile were there checking their licensed spectrum to make sure no one encroached on their airwaves. All really cool stuff, but I digress since the purpose of this is to tear apart the bracelets given out.

Upon walking into the arena, I noticed that every seat had the 'Strength In Numbers' shirts along with bracelets masking taped to each seat. There was obviously some magic to these bracelets; they couldn't just be silicon bands with plastic tops. 

After getting my initial work done, I settled down in the media section and waited for the game to start. John Legend came out to sing the national anthem, the lights went down in the arena, and all the bracelets started lighting up. Not only were they lighting up, but the the colors were coordinated by section where some were red and some were blue. It was an amazing sight. 

Throughout the game, the bracelets would again light up. Also, clapping your hands seemed to set off the lights on the bracelet. When I had a few minutes break between running around and working, I used LightBlue to sniff the BLE in the area since I considered the light-up coordination was done via a BLE mesh network. Could it be that Pixmob was able to manufacture these bracelets with BLE at such a low price that they can be giveaways? Upon scanning, I found hundreds and hundreds of unnamed BLE devices around me. Red herring?? Also, is it possible Pixmob also threw in cheap accelerometers for the hand clapping detection? 

 Fast forward to the next day after work and I am home with this bracelet that still lights up when I clap. It's ready to be opened up. 


Two CR2032 batteries to power the device.


First thing I notice when cracking it open is the RGB in the center. Pretty standard lil' dude. Then I notice, no RF. So there is no BLE? Instead there is an IR reader. Could all the color coordination by section be done by IR? I guess so!

On the sides, we see 2 more RGB LEDs completing the complement of 3 RGB LEDs on the device.

I then noticed SW1 (the white cylinder). It's too small for pictures, but there are 2 leads coming out of it. One is a thick lead connecting to metal on the outside perimeter of the cylinder and one is a tiny thin wire in the center. Ahh!! The ol' spring contact trick! Inside SW1, the thin wire goes to a spring floating in the center. When the user shakes the bracelet, the spring in the middle makes contact with the metal on the perimeter which allows the microcontroller to know 'hey, time to light up these RGBs!' 

Speaking of microcontroller, what powers this guy? Seems that it is a MC81F4204 by a company called Abov. The MCU is a CMOS based 8-bit MCU with 4k of flash and 192 bytes of RAM. It has a 12-bit ADC and other basic features. The part doesn't seem to pop up on Octopart. Wonder how cheap they are in quantity. You can also see solder pads around the MCU. The geek in me hopes they are pads for a scalloped RF module incase you want to get real fancy with the board, but it's probably just for a larger IC along with programming headers (J1).

Overall, a cool little device with some nicely done DFM to bring down cost. 
Hopefully I can grab more when I'm at game 2 so I can hack em together and see what I can manage. 

Go Warriors!

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