Looking for someone with a scope and access to the OrangeRX DSM2 "compatible" receiver, who can figure out which pin, if any, has a direct PPM signal that can be tapped on these ?

If you have a scope and are willing, I will consider shipping a receiver to you.  But I guess you will need a DSM2 TX to test this in action ?

Rajesh, Ismail... others who do circuit stuff for a living ?

Anwar,

I have the equipment but I don't think its worth the effort shipping the receiver. If you have a multimeter you could figure it yourself.

Depending on the brand, most receivers have center pin as either GND or Power. So you need to check the pins on either side of the center pin. Have the multimeter to measure voltage. Touch the meter's black on the center pin and touch the red on the left pin. If you see a solid 5V (or the battery voltage) then the right pin is signal. If the voltage measured is less than the 5V (or the battery voltage) or if keeps moving up and down then its obvious that the left pin is signal.. Similarly repeat the same for the right pin and confirm your findings.

If I were you I would just connect a cheap servo either way and find it out.

-Ismail

Err, I guess I did not explain myself well The other one is too simple, and that would be PWM only, not PPM, right ?

What I wanted is the combined/encoded PPM signal of all channels !  I really missed out the word "encoded"

What I am looking for is what is shown in this page for various receivers :

http://paparazzi.enac.fr/wiki/RC_Receivers_and_Radios

Basically, to figure out which MCU/chip pin has the full encoded PPM signal.

Oh.. I see your point. Sorry, I missed it.

Do you have the receiver open? and do you have access to the chip ID numbers? I think the manufacturers probably scratched up the chip IDs.

I opened one up, and there are two chips. I will post the details after I find my magnifying glasses.

Also, seeing the MCU legs which are SMT, not sure it would be possible to tap out without significant soldering skills. Came across the following post on HK forums.

http://www.hobbyking.com/hobbyking/forum/forum_posts.asp?TID=14646&PID=112068

Do you think this second post makes sense ?  I am not sure I can see how this works, although this seems to be an easy way out. 

Of course there are PPM encoders available, and I have one, but this is for someone else who needs this multiple times, if I can get this to work.

Anwar,
You have to trace the radio circuit output that enter the mcu.
Please look at http://www.rcindia.org/radios-and-receivers/inside-esky-transmtter/msg48542/#msg48542

The three wire (Red Black and white) generally feeds the Tx Module. the third wire other than red and black is the signal. This has to be measured with respect to Black.

You can open up the receiver, Look for the low pass filter (to remove carrier from signal). It may be build in micro-controller (uc) itself. Or on the other hand you have to trace out the demodulated signal output track that goes in to uc.

I prefer to trace from the transmitter end. Inside the transmitter, you can check the signal in the transmitter module (Coded). Without oscilloscope, you can see the result by recording the signal using a simulator hack cable or feed the signal to sound port (Ground and Signal) of computer through 1k/10k resistance voltage divider. Just record through Goldwave and you can see the waveform.

You may use audacity, but I prefer goldwave. It's the best to observe encoded digital data. Please don't couple through capacitor.

If Oscilloscope is available, life will be easier. At <8K Pico-scopes(Computer required) are available. <15K Digital Oscilloscopes available and <35k, 300MHz Storage Scopes are available.

Oscilloscope software are available that can convert Computer to OSC using inexpensive electronics components. Please check. Once you get the bits pattern, from Tx, you can compare the comparative signal of Tx & Rx in two channel of Oscilloscope. as Tx Data = Rx Data

Thanks

Kalyan - Thanks, but tracing it on the TX side does not help me at all.  This is needed on the aircraft (quad, tri etc) side, so it has to be on the receiver side.

On the receiver side, it should be coming out of the MCU, since this is a 2.4Ghz system. The 2.4Ghz signal must be going into the MCU (after some preprocessing, and either the various channels come out as PWM, or if we are lucky, a combined/encoded PPM signal will come out of one of the MCU pins. 

I believe this is a problem that has been cracked already if you use satellite receivers. Some quadrotor controllers I have seen decode the satellite data stream themselves, no need to convert it to serial ppm. There should also be code available to convert to ppm stream if required. A google search throws up lots of results on these. I'm not a spektrum user and haven't looked into any of these in detail, but know there is enough info readily available on the net.

Here's one of the google results.
http://code.google.com/p/uavp-mods/issues/detail?id=4

Hey Anwar,
If you could explain (in plain speak) exactly why this information is requested, maybe we could learn a few things. Right now, its going way above my head.

regards
Pankaj

Interesting... never thought of that.  The satellites are double the cost of the 6ch receivers themselves though   and that does not make any sense !

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=13418

Basically, if you want to feed 4 or 5 channels of control inputs from your receiver to a MCU (say an Arduino), then you will have to use that many pins on the arduino, which reduces the number of usable pins for other stuff.  So instead of feeding in 5 separate PWM (servo type) signals, you feed the encoded PPM signal which has all the channels in a single wire, there by using up only one pin on the Arduino, freeing up the other pins for other tasks (usually outputs to various devices, like speed controllers on quads, hex rotors etc).  That is the basic thought process behind this.

Yes, that post makes perfect sense and it is a clever way of doing it. There is only one thing that concerns me but I assume it should be fine.

If there are any inter-channel delay between the channels, then that delay time is also added to the final output pulse time from the diode network. However, given that the inter-channel delay is constant the overall operation should be proportional.

The diode network should work on both positve and negative shift receivers. The MCU should trigger on edges from this network to decode the channel data.

-Ismail

That makes life so much easier ! 

So what are the parts that would be needed to get this done ? 

It would be great if you can post a rough ("drawn on tissue paper"!) schematic of the same.

Attache a pic of what I have in mind. Please refer the original post about the channel order. It may vary for each brand. The circuit is a simple diode OR gate.

Let me try this out first.

Hi anwar,
i'd like to hack serial signal from orange rx for a video gimbal application, did you find a working solution?

Of course the Rx is to be powered up. The diode adder is the best idea.
Surely it will work.

I had tested it, and it seems to work.  The issue was that since this is only a 6ch receiver, and we are skipping alternate channels, one could only get 3 workable channels out, which was not enough for what we were attempting.  Another minor issue is that one would need to use PMIXes move the stick information from the channel that corresponds to a stick movement to the alternate channel we are using on the PPM tap. 

Should work on a 7 channel receiver, if you want 4 channels output.

thx,
i think i'll stay with 1 channel / 1 arduino in...