PPM Decoding Techniques

[charles0198]

Lets dedicate this thread to the PPM decoding techniques and methods only, and restricted to hobbiest (No commerically selling guys!).

Since I am interested in this project using PIC I have found 2 such projects only. One is by Bruce Abbott (http://homepages.paradise.net.nz/bhabbott/decoder/rxdec6.asm) and the other is Rustre's multiservo decoding code(http://216.239.39.104/translate_c?hl=en&u=http://mathieu.agopian.free.fr/prog_pic/servoter/&prev=/search%3Fq%3Dhttp://mathieu.agopian.free.fr/prog_pic/servoter/%26hl%3Den%26lr%3D%26sa%3DG). Both these codes are very good but have limitations.
Bruce Abbott's code it doesn't have a very high resolution but has DSP to overcome glitches.
Rustre's code have interrupt driven decoding only with 40MHz clock but no DSP included.

[MZanders]

You can also do it in hardware using FPGA's or perhaps a CPLD. This way you put this (perhaps vital) function in a more robust carrier and it's a lot faster, too. Interfacing with a µC or DSP could be done through a simple SPI interface. Also a lot less processing overhead so you can put more computing power in the PIC or whatever you'll use.

Also think of where you want to go with the decoded information.
1. PPM > µC > PWM for intelligent servo control (= RX brain update)?
2. PPM > µC > PPM for TX brain update?
3. PPM > µC > EIA232 for PC interface (ie FMS interface)?
or a combination of the above? (2+3 seems interesting)

I've been looking at the above and am trying to squeeze it in a CPLD. But it won't be for immediate implementation.

Cheers,
Maarten