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Old Feb 25, 2007, 10:41 AM
Vefa is offline
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How to hack R/C receiver GWS RD8SL


Does anyone know how to read signals coming from all of the channels from one point on the circuit of the GWS RD8SL receiver?
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Old Feb 25, 2007, 10:59 AM
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Sure, at the antena's amp. Thats pretty much the last place all the signals are going to be at a single point. Of course, thats an unprocessed signal that won't be worth much.

What is it you are trying to do?
Old Feb 25, 2007, 11:33 AM
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I am trying to read all the signals thru a microcontroller so that I can record stick history of a pilot. I found a point. However, when I touch it with my oscilloscope's probe the servo that I connected to channel 1 was driven to its end position. It was a very clean signal and it seemed like pwm signals of all the channels.
Old Feb 25, 2007, 12:25 PM
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Sounds like you have already found the problem, then. pulling off the signal on the back side of the amplifiers is likely to destabilize them, and/or corrupt the data to the reciever's cpu. Were you using an O scope probe ment for high freq?

Anything you do to the reciever, including probing it is going to effect both it's resistance and impedance, so to get a clean usable signal, you'll need to retune the amplifiers and issolate the recording circut, or it will feed back on the amps and the data and cause errors and drifts, like having that servo drive it's self.


You might have better luck taking the individual signals and recording them after the CPU. The output is much less sensitive, and wouldn't run the risk of causeing the plane to crash by destabilizing the antena or frequency filter.
Old Feb 26, 2007, 03:26 AM
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Vefa,

The PPM signal you're looking for is the only direct connection between the radio (the FM demodulator section) and channel demultiplexer (the second chip, close to the channel pins).

As for why your scope affects the signal, there are two possible explanations:
1) you're not looking at the proper PPM signal
2) your scope probe has huge input capacitance (as a 1:1 probe typically has, well above 100pF). In that case, use an attenuating (10:1) probe, whose capacitance is below 15-20pF

Serban
Old Feb 26, 2007, 05:32 AM
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Receivers are $20. Why would you need to use the same one that is controlling the plane? Anyway, The recording equipment must be too heavy to fly. A second receiver on the same channel would read almost the exact same signal, definately the same control inputs. Splitting the signal should not be an issue.
Old Feb 26, 2007, 06:02 AM
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I would move this to DIY electronics.

What you want to do is trivial, but I don't know the exact pins to hit on the board.

You should be able to pick up the composite data off the clock pin of the output decoder chip.

If you can ID what exact chip it is, look up its specs and find out which pin is the clock.


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