Help identifying PPM source in TX (For FrSky Hack)

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Help identifying PPM source in TX (For FrSky Hack)

Postby bapgood » Mon Oct 25, 2010 10:02 pm

Is there an easy way to identify the PPM signal coming to the existing module?

I'm looking at doing the hack module on an Airtronics MX-3FHSS surface radio as well as possibly a Spektrum DX2.0 and the a native 2.4 JR9303

Thanks Bradey
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Re: Help identifying PPM source in TX (For FrSky Hack)

Postby kneedrag » Fri Oct 29, 2010 9:21 pm

Do you have an oscilloscope. That is the normal method of tracking the PPM signal down.

The other suppising one that works is Google and doing a search for installing hack modules in xyz transmitter. Someone usually has done it before and documented the process.

If you don't have much luck that way there is a bit of software that you can load which makes your PC's audio port a scope. Don't have the link with me right now. You will just need to rig an audio wire into a probe.
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Re: Help identifying PPM source in TX (For FrSky Hack)

Postby bapgood » Thu Nov 04, 2010 6:06 pm

kneedrag thanks for the reply i got one of the engineers at work to test with an oscilloscope to find it....and yes i struck out with google :)

seems now the issue is ppm frame rate....which the airtronics is to fast....so now im wondering if a simple circuit could be built to take the existing ppm signal and output a usable signal.
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Re: Help identifying PPM source in TX (For FrSky Hack)

Postby Flash1940 » Thu Nov 04, 2010 7:00 pm

Look for the signal down on the trainer jack. When you insert a 1/8" plug in there....the signal should be on the tip with respect to ground. at the same time the power is switched off the onboard rf circuit. Like a DSC cable.....the signal goes down the shielded cable to your RX.

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Re: Help identifying PPM source in TX (For FrSky Hack)

Postby bapgood » Thu Nov 04, 2010 7:18 pm

Flash, thanks and i guess i should have clarified....i was able identify the ppm signal off the pcb as there is no trainer jack on the tx (airtronics surface mx-3fhss)

Bradey
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Re: Help identifying PPM source in TX (For FrSky Hack)

Postby RCModelReviews » Thu Nov 04, 2010 10:17 pm

Unfortunately many surface radios have a higher frame-rate than those designed for RC planes.

This is often because the lower number of channels allows for more frames per second.
RCModelReviews.com, just the facts.
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Re: Help identifying PPM source in TX (For FrSky Hack)

Postby bapgood » Thu Nov 04, 2010 10:27 pm

Bruce,
I was afraid of that :(....the hack module works fine in my spektrum dx2/3.....but the airtronics tx fits a feels a lot better plus it has 18 models vs 4 for the spektrum....so fit, feel, and models is the main reason i want to get it to work.

Do you have ideas for an intermediate circuit to sample the existing ppm signal and generate one that is compatible?

i have googled to death the sanwa chip used hoping to reconfigure the output but i couldn't find a thing.

i will be hooking it back up to the scope and documenting the ppm signal in the next day or so.
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Re: Help identifying PPM source in TX (For FrSky Hack)

Postby palton » Mon Nov 22, 2010 9:01 am

For the ones not owning a scope.

I use another way doing it. I read about it at the forums at arduino.cc (http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1199165055) .

If you happen to own an arduino (http://www.arduino.cc this little microcontroller costs like 30$ ("uno") in somw flavor (there is a huge amount of arduinos and clones) something like that and is attachable via USB directly), it's another way of doing it. Works for common PPM pulses at least.

Just put a few lines of codes into the microcontroller ( as seen in the example according to link, to read the PPM pulse in one pin. Code is downloadable via USB, no programmer needed for the micro controller.

Physically attach two pins to the object that needs to be ppm hacked, receiver, transmitter etc, gnd and the pin receiving the pulse. If pulse needs to be reversed, shifting positive/negative pulse. Then the pin values are replaced for example, HIGH could be replaced with low in the code, then this will shift the read pulse.

Then you can also read the values sent to the PC serial port via USB as well with IDE's serial monitor interface, let the internal onboard LED on the arduino blink as well, if pulse is there etc.

Simple but works pretty well. I have been playing around with it testing both negative and positive pulse on my 9X transmitter with er9x firmware, as it's configurable in the code.

I just thought this could be good to know for someone, if they have a need and missed this possibility. A scope is a scope, but this reads the ppm pulse values as well and could be used for other purposes as well, generating pulse also. Just thought it was worth mentioning as an alternative way...
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Re: Help identifying PPM source in TX (For FrSky Hack)

Postby aesmith » Mon Nov 22, 2010 11:41 am

I've just downloaded and installed a free PC Oscilloscope program, that uses the sound card input as the signal source. Very limited of course, but it is well up to displaying the transmitter's PPM stream, or PWM servo signals. All that would be needed is to divide the voltage down.

http://www.zeitnitz.de/Christian/scope_en
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Re: Help identifying PPM source in TX (For FrSky Hack)

Postby peril » Tue Dec 07, 2010 8:23 pm

With reference to finding the PPM signal on a JR.

I identified the three wires that go to the RF module then measured the voltages in each with a digital volt meter. One wire was the negative lead (ie. no voltage), the middle wire was a low voltage of around 0.5v (PPM Signal), the other was obviously the positive lead @ 10.5v.

Simple but effective.
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