OKAY so this this the Square Panda spelling thing. The idea is that this interfaces with tablet apps for little kids to spell words, and it can detect what they spelled on it. I'm gonna tear it down.
I'm gonna try adjusting the visibility for this thread after this so you should only see this one post.
The top part doubles as a storage unit for the letters and as a platform for the tablet.
Interestingly the letters don't seem to be magnetic... I figured this would be using hall effect sensors or something similar
main chip and antenna on the upper left, a small chip + some passives for each letter, and a button in the top-right.
It calls itself an SP-0042 Sensor PCBA, revision 12P5, from 2017.
So each of the chips for the letters are MC74HC4051 analog multiplexers/demultiplexers.
and our main chip is an nRF51822: That's a BLE/2.4ghz SoC from Nordic Semiconductors.
It's a 16mhz Cortex-M0 chip, 256/128 kilobytes of flash, 32/16 kilobytes of RAM.
There's an unpopulated 4-pin connector nearby. I wonder if this is for USB (in another model) or if it's for programming?
So the letters have a little grey sticker on the back of them. I can't detect any magnets under them, so I guess I gotta remove it.
So here's the fun part:
You know what's in the letters?
Nothing. Just air. No NFC chips, no magnets.
So what I think is actually happening is that these stickers are conductive, and this thing is capacitive.
