Multiplexed PWM signal from Futaba rx?

[andrewbirkett]

Has anyone ever cracked open a Futaba receiver to get at the raw multiplexed PWM signal? I'm putting an Atmega microcontroller in an RC plane, and I'd really like have a single PWM line coming out of the receiver into the microcontroller, and then I'll do the decoding into individual channels myself. I've seen various papers and sites alluding to people who've done this, but I've not seen any concrete examples. I only got a 6-channel receiver recently, and it'd be nice to know that I wasn't the first person to open up the receiver and start prodding around with my oscilloscope! Thanks for any advice. :-)

[AnthonyRC]

I think that you're looking for a PPM signal, not a PWM signal.

Never done it with a Futaba, but I have the magic point for a 6 channel Hitec electron if you are interested.

[Bob Blackburn]

The raw ppm data will be present on one of the legs of the ic that is connected to the signal pins of the servo connectors.
This is the "decoder chip"
There are various decoder chips used in different receivers but the raw ppm still has to go in on one of the pins.

If you are still not sure then there is a thread somewhere about taking the signal from each servo output and reconstructing the ppm.

I never understood why they wanted to do that.

[vintage1]

If it uses a 3361 or equivalent, the standard practice is 'audio out' is pin 9, that gets squared off by a discrete transistor, and then applied to the clock input of the shift register decoder.

[andrewbirkett]

Thanks for the replies. I went ahead and cracked open the receiver tonight and have identified the signals I need. I've put some photos and explanation up at ...

http://www.nobugs.org/engineer/uav/futaba-rx.html

[deh6]

I have a R127DF where I bring the serial signal out to servo position #7. It requires one trace cut and one wire.

With the rcvr top facing down, and the servo pins on the right (the bottom triplet of pins is servo #7), cut the trace going to the leftmost pin (signal pin for servo #7. Add a jumper wire from the pin to the bottom end of the 4.7K resistor (marked 472) located on the lower left side of the pc board.

I feed the rcvr power from the 5v reg power on the micro (Freescale 9S12E128) and input the serial line to an input capture on in the micro. Works just fine.

[vintage1]

Thanks for the replies. I went ahead and cracked open the receiver tonight and have identified the signals I need. I've put some photos and explanation up at ...

http://www.nobugs.org/engineer/uav/futaba-rx.html

Ultimately you can remove the decoder board and get what you need from the signals going to it.

Then repalce it with your PIC decder...and voila! A really good futaba..