DSM2/DSMX Remote Receiver Protocol

I’ve been playing around with my transmitter a lot recently as flying season is starting up again and the darn thing isn’t working well.  Likewise, the receiver I’ve just installed in the Pulsar refuses to bind to my radio.  So a big fail all round by Spektrum, which has lead me to seek alternative solutions.

The AR8000 Receiver with a remote receiver attached

I’ve seen a few forum threads discussing the serial protocol used by Spektrum’s remote receivers and it seems pretty straight forward to collect the data from them; bypassing the main receiver completely.  Unfortunately the only decent write up of the details that I could find was a bit out of date, and only covered the 7 channel case.  So here is what I’ve learnt from poking this device with an oscilloscope and a logic analyser for a few hours. (more…)