2.4ghz: How to read 7 channels with one wire (NOT PPM) with Spektrum modules...



Since i got my new 2.4ghz spektrum radio (I FALL IN LOVE) i always wonder how the daughter receiver send data to the mother, maybe PPM? mmhh not! With a little help of an oscilloscope i started to reverse engineer the protocol used, well i saw only steady digital signal with lows of 8.6 useconds, that responded to the movements of my radio, so i quickly realize that is some kind of serial communication, and i did the calculations (1000000us/8.6us=116279bps) and i thought that maybe the serial speed was 115200bps. So i attached my FTDI cable and start analyzing the data, and i got this:



Spektrum daughter board is sending 16 bytes of information using a serial com. running at 115200bps. As you see in the picture above, the two first bytes are the preamble or sync bytes (0x03, 0x01). The data comes in integers that response precisely in the order is labeled in the picture...

So Paparazzi users this is a way to switch 2.4ghz (only in American), the back of my Specktrum radio says: "NOT FOR USE IN EU", uuh!

I hope somebody can do something usefully with it, enjoy!

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Tags: spektrum

Comment by Kenny on February 11, 2011 at 5:18pm
Well reports are that the Spektrum satellite rxs bind and function with the orange main rxs, so it follows that it would be the same. These must be kind of new. If I had seen them when I ordered my orange rxs last year, I would have bought some to try.
Comment by Gerd Verreycken on July 19, 2011 at 9:21am
I have managed to decode a AR8000 satellite receiver (DX8 into Arduino mega 2560). I am thinking to use an inversed version of the same protocol and send serial data into the master receiver and use it as a 8ch servo controller. By binding the master on a diffrent channel and not use that channel....Thanks Jordi for the great idea!
Comment by Gerd Verreycken on July 19, 2011 at 9:29am
My personal opinion is that the orange DSM RX'es are only good for foamy parkflyers. Most of the rangetest I have compared the range and diversity of the AR500 AR6100 AR6200 AR7010 AR8000 4CH orange 6CH orange and 6CH orange with sat. Range of the orange was allmost as good as the spektrums but they recovered very slowly from signal losses. They all froze for about 10 seconds when experiencing first range issues.... I have reserved the oranges for indoor and shockflyer use only.
Comment by John Fressinet on August 9, 2012 at 5:39am

Hi ! this is more a question than a comment.

Some one uses the Spektrum satellite receiver on the APM2 ?

The channels are not active in Mission Planner.

Comment by Joe on August 11, 2013 at 6:40am

Jordi must have fallen out of love since there is NO support for Spektrum serial in APM 2.5 instead we have PWM to PPM converter and back to numbers when S.BUS OR Spektrum would be far more reliable than PPM, not kidding, why has that not been addressed ?

If the code exists for PX4 why isn't it available for APM 2.5 ?

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