Kerry Wong writes:
I was quite intrigued by the S-Pen that came with my Samsung Galaxy Note 4. According to the specifications listed on Samsung’s site, the S-Pen supplied with Samsung Galaxy Note 4 he S-Pen supports 11 bits (2048 levels) of pressure levels and can be detected at a 15 mm hovering distance from the phone surface.
Kristofer at Android Authority had done a teardown of the S-Pen a couple of years ago (it was an older model, but the principal should be largely the same). And as we know the S-Pen works similar to an RFID which is passively powered from the electromagnetic field generated by the phone. I thought it would be interesting to dig a bit deeper to see what the communication patterns look like.
Because the S-Pen is powered by the RF field via inductance coupling, we can use a pickup coil to detect the signals passed between the pen and the pone without having to take apart either. To do this, I dissembled a small speaker and used the voice coil as the pickup device.