Honor impedance from TRRS jack (a.k.a. make FF/rewind buttons in headset cable remote controls work)
asked 2014-08-05 16:27:18 +0200
It seems jolla/sailfish honors control input from the TRRS headset jack in general. However with my Sennheiser cable remote control I'm only able to resume/pause music / accept a call respectively, however the rewind/forward buttons do nothing. I guess that's due to it's nature, that the working control sequence (play/pause / accept call) is far more easy to implement (just shorts the microphone) and therewith easy to detect. According reverse-engineering of those headsets, shorting it through a 220-ohm or 600-ohm resistor acts as a rewind/fastforward button which I guess just isn't implemented by Jolla. My question now is: Is that a hardware limitation or is it possible to detect those impedance changes in software?
Some further reading about the nature of cable remote controls: http://shaddack.twibright.com/projects/reveng_RemoteControlHeadphones/