PPM Polarity
Posted: 18 Apr 2018, 10:49
Hi All
I'm trying to finish off the documentation for a proportional encoder project that I've written and there is one thing that I'm not certain of, the correct description of the PPM polarity.
In the below screen-shot from my logic analyser of two ppm streams, the top one is typical of a Futaba and the bottom one typical of a JR transmitter. I've always called the top one negative polarity as it is mainly at ground and the bottom one positive polarity, but there are conflicting descriptions on the web.
To get a Spektrum DM9 module to work in a FrSky Tx you have to choose + polarity (and 400uS pulse), that would suggest the above description is correct. But if I put the waveforms into a Phil_G ppm monitor it says the opposite!! And Phil is not wrong very often.
I've got all the modules that I've tested to work OK (FrSky, OrangeRx, Spektrum, Corona, Multi-protocol, Futaba 35MHz and 2.4GHz and JR 35MHz), so I haven't a problem with the programming or the hardware, it's just I don't want someone saying I've got my descriptions wrong.
Thanks
Mike
I'm trying to finish off the documentation for a proportional encoder project that I've written and there is one thing that I'm not certain of, the correct description of the PPM polarity.
In the below screen-shot from my logic analyser of two ppm streams, the top one is typical of a Futaba and the bottom one typical of a JR transmitter. I've always called the top one negative polarity as it is mainly at ground and the bottom one positive polarity, but there are conflicting descriptions on the web.
To get a Spektrum DM9 module to work in a FrSky Tx you have to choose + polarity (and 400uS pulse), that would suggest the above description is correct. But if I put the waveforms into a Phil_G ppm monitor it says the opposite!! And Phil is not wrong very often.
I've got all the modules that I've tested to work OK (FrSky, OrangeRx, Spektrum, Corona, Multi-protocol, Futaba 35MHz and 2.4GHz and JR 35MHz), so I haven't a problem with the programming or the hardware, it's just I don't want someone saying I've got my descriptions wrong.
Thanks
Mike