AirPods Charger Teardown and Reverse Engineering
Freddie Temperton (via Jon Masters):
One thing we noticed when playing with the AirPods is that your phone knows the charge state of the AirPods individually, as well as the case itself. How were they doing this? Our interest was piqued! We also noticed that if you don’t have either AirPod in the charger cradle, the phone is unable to read the charger cradle charge state. It was very unlikely that the case has another Bluetooth radio in it as that seems total overkill and power hungry, so we discussed other options. As there are only 2 contacts between the charger and AirPods, we theorized they must be using a form of powerline communication and hijacking the radio in one of the AirPods to transmit information from the charging cradle to the phone.
[…]
With the first glimpse of the innards, we knew this was a lot more than a simple dumb charger. There’s an ARM Cortex-M0+ in there!
[…]
The little button on the back is actually a whole custom assembly. Two metal contacts are moulded into a piece of plastic to contact with the springs on board, then a SMD switch soldered on. The button that presses down even has a tiny milled metal insert for pushing the button! Very impressive ME work!
