Beta test new servo input firmware for ArduPilot MEGA













The PPM Encoder team has been working on a new servo input to ppm firmware for the PhoneDrone board and any future boards using the ATmega32u2 chip.

Since there has been reports of problems with the old APM firmware (PPM encoder problem, loosing CH3 again with new APM board) when used together with receivers that has synchronous changes on multiple servo channels. So Olivier ADLER and me decided to back port the new atmega32u2 firmware to the ATmega328p chip used in APM boards.

We now feel that the new and hopefully improved firmware is ready for public beta testing. Source code and compiled firmware are available in the official APM repository (Unified ArduCoder). Please read the readme.txt carefully before usage and report any problems.

Future updates for the new firmware will have PPM pass-trough for receivers with PPM output and also possibly native support for Spektrum satellite receivers.

Happy flying!

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3D Robotics
Comment by Chris Anderson on July 31, 2011 at 12:24pm
Thanks for posting this! For all those who would like to use the new code, you'll need to load it with an AVR programmer. Instructions are here:

Comment by Andrew Tridgell on July 31, 2011 at 1:54pm

Thanks John! I've been interested in switching to PPM to make my cabling simpler. Do you know if this will work with the FrSky CPPM receivers, like the D4FR?

Also, if I flash this firmware onto my APM, will I still be able to use 8 separate PWM cables if I use a receiver that doesn't do PPM?

Comment by John Arne Birkeland on July 31, 2011 at 2:28pm

The PPM pass-trough functions is not available yet, but the plan is for the PPM pass-trough to be activated if channel 2&3 inputs are shorted together with a jumper. So you will have normal 8 channel PWM and when you insert the jumper you get the PPM pass-trough mode.

Since the PPM function will be a pass-trough of the PPM signal, actual PPM decoding is performed by the main APM code. I do not think APM has CPPM support yet.

Comment by hazy on August 4, 2011 at 7:39pm
I notice that there are only one hex file "Encoder-PPM.hex" in the svn repository. Is that file compatible with both Atmega328p and Atmega32u2?

Comment by John Arne Birkeland on August 5, 2011 at 4:45pm

The <Unified ArduCoder> project is a replacement for original APM servo firmware, and will only work with the 328p. The 32u2 also has to run the Arduino USB-To-Serial code (LUFA) so a common project for both is not feasible. But the underlying core library with servo input and ppm generation support both chips.


Comment by John Arne Birkeland on August 5, 2011 at 4:52pm

PPM passtrough added:

If your receiver has a PPM sum signal output, it is now possible to pass on the PPM signal from servo channel 1 to the PPM pin. To enable PPM passtrough, short the servo input channel 2 & 3 signal pins together using a jumper strap.

Please note that the PPM sum signal must be compatible with the APM autopilot PPM decoder (8 channel standard PPM) since the ppm signal is not decoded in the PPM encoder and passed straight trough to the autopilot.


Comment by Björn Pettersson on August 20, 2011 at 3:17am

I'm all new to this, but I'll try the ppm passtrough on a jeti rsat when I get my hardware :) Seems it will send 8ch ppm in direct mode if the Tx module detects 8 channels. Mpx royal pro 9 here so no problems with that.

Comment by Ravi on August 28, 2011 at 11:12pm

Hi john, i am able to get PPM output from a pin on Futaba 7C 8channel receiver. is the PPM sum signal compatible with the APM2.22 PPM decoder or i have to decode it. actually i am more of an aircraft engineer and less of a electronic engineer. the sihnal is coming from a Futaba 7C Tx onto a 8 channel Futaba Rx. thanx for modifying the APM code so that a direct single wire PPM signal can be input instead of 5 PWM channels to APM. great job!

Comment by Olivier ADLER on September 9, 2011 at 4:30pm


Bjorn, Jeti Rsat is working without problem, i testet it in 8 channel direct mode.


Ravi, i answered to your question about ppm in my meet the developers profile here :

Comment by Alfred Riopel on October 4, 2011 at 1:05pm

Is it possible to use the JR/Spektrum Satalite receivers for the PPM sum input? If not, any plans to implement it?


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