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Old Aug 27, 2010, 09:34 AM
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Question
PPM to TX problem with arduino generated PPM

Hi there, I opened a thread in the radios subforum, maybe I should have put this thread here..

I can control my simcable with the generated PPM-signal, but my transmitter won't read it correct.
since the manual tells that a trainer/pupil connection should be possible, i thought the signal that comes from the transmitter should accept the same signal on the input pins... but no success so far.

maybe someone with experience in connecting transmitters can see what's going wrong.

this link goes to the thread in the radios subforum..
http://www.rcgroups.com/forums/showthread.php?t=1298090

too bad, if it's only possible with another transmitter like spektrum dx7 or similar.. more costs for transmitter and also some receivers, some linear servos and gyros.. several 100 bucks I guess.


thanks!
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Old Aug 27, 2010, 04:25 PM
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Have a look at my Arduino to RC Tx implementations. Works fine with Futaba. Might give you some ideas.

http://www.ianjohnston.com/index.php...bbies&Itemid=8

&

http://www.ianjohnston.com/index.php...bbies&Itemid=8

Ian.
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Old Aug 27, 2010, 04:48 PM
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It took me a long time to discover that a Futaba transmitter fed with a ppm signal on the trainer port is quite fussy about the pulse widths and will drop out of trainer mode if they are too long or too short.

Peter
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Old Aug 27, 2010, 05:48 PM
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thanks for the replies!

Ian, I see you're using Interrupts for the frame timing, I will try this approach.. I tried the easy way first, as with constant timings I hoped there would be not too much difference, but I already recognized the calculations take their time too, maybe too much or just not constant enough..
it's late now, but I'll give it a try tomorrow ..and look for other things in both of your links..

Peter, I hope and guess my transmitter is not complete out of trainer mode, since the servos show at least shuttering.. might be I am wrong, so I will try to let the microcontroller increase the pulse widths step by step.. maybe every 5 seconds, hopefully this will show if there is a specific pulse width that will work.

Thanks so far!
I will report the outcome..

Dave
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Old Aug 27, 2010, 07:11 PM
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Quote:
Originally Posted by IanJ View Post
Have a look at my Arduino to RC Tx implementations. Works fine with Futaba. Might give you some ideas.

Here & here.

Ian.
Bit of a shame to have to redo the whole transmitter, so to speak, but it does show that they are quite overpriced, I guess.

Your solution does potentially open up lots of opportunities to multiplex controls over similar channels, e.g. you thought you had a 6 channel system but with some clever use of bits you could now have (throttle), (aerolon), (elevator), (rudder), (altitude hold on/off + gps position hold on/off + gps come home on/off + gps next waypoint on/off + parachute deploy on/off), (camera pitch 16 steps + camera shutter interval 2 steps + camera shutter) which still is using 6 channels but now is transmitting 12 controls Of course your Quadrokopter flight controler source code needs some modification to have a channel mapping AND masking table to be able to assign the relevant bits of channel 5 to their related 5 controls, and those of channel 6 to its 3 controls.

Would be even nicer is you could selectively add information to channels on the master through the trainer port, but I think surgery remains the only options to do that as done in the "Sexpander" ATTiny13 solution by someone in the Mikrokopter community.
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Old Aug 28, 2010, 06:51 AM
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Quote:
Originally Posted by Arthur P. View Post
Would be even nicer is you could selectively add information to channels on the master
Side note - I am working on an Arduino based PPM mapper. It's at testing stage now.

2 PPM stream inputs.
1 PPM stream output.
Ability to choose how many outputs and control over PPM timing.
Ability to pick and choose which channels (in any order) are sent to the output stream.
Servo timing input (read servo timing) 2 channles can be mapped in.
Servo drive output (pick any 2 channels to drive servo's directly)
PPM stretcher.
Invert PPM output.
AC coupled PPM input stream option.
etc etc etc......other stuff I might have forgotten!
All configuration done through a Java app on a PC.

Ian.
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Old Aug 29, 2010, 04:19 PM
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ok.. I tried the interrupts and the pluse width..

timing gets better with timer interrupts, but no success at all
I scanned pulse widths from 200 to 500..
I think it had least shuttering around 300.. but the problem must still be somewhere else..

I measured voltages on all pins of my transmitter with nothing connected and no buttons pressed..

I hope it works to insert attachments directly as picture..


from pin 1 to 5 it's 0.3 Volt
from pin 1 to 2 it's 3.0 Volt
from pin 2 to 5 it's 3.3 Volt

if I connect my arduino signal to 1+2 the power bar goes down to 1 red LED.. if I connect it to 2+5 it remains at the same level as with nothing connected.. maybe I need to give some power into the trainer port? ..but how and which pins..

the manual says the PPM signal comes from 1+2 and should go to 3+4.. I guess, there is only a thick line going from between 1+2 to 3+4.. when I connect 1+2 to the simcable it works and I can use the transmitter as gamepad.

when I record the signal that comes from the transmitter, it shows a PPM signal, as you can see in attachment 2..

Full Size: http://www.sendspace.com/file/k42gce


frame length should be 29,5 ms.. right?
everywhere else I read it should be 20 - 22.5 ms..

thats how far I could get this weekend.. I hope you have any idea what's going wrong..


Thanks,
Dave
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Old Aug 29, 2010, 04:37 PM
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moved to previous post
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Old Aug 29, 2010, 06:38 PM
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tomorrow I'll scan and attach the page of the manual about the trainer cable and I will record my generated signal, so you can compare the original to the generated one.

If I can get a good camera tomorrow, I will also attach some photos of the inside of the transmitter.. maybe it is possible to connect the wire directly to the rf unit, maybe with switch that filters/overrides the original signal.. although I think there should be a possibility to use the trainer port. I sent an email to Nine Eagles and asked where I could get an original trainer cable, no answer yet, maybe I'll have to ask a dealer that sells those Nine Eagles products..
I couldn't find one anywhere on the internet, the simcable is for esky transmitters and I had to change the wires to make it work.
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Old Sep 01, 2010, 09:03 AM
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im still having problems with mine generating a 100% compatible pulse train with a spektrum dm8... i set the project aside for a bit and ordered a JR module to see if it has anything to do with the inverted signal. i'll give mine another go as soon at the goods arrive!
-sj
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Old Sep 01, 2010, 06:44 PM
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I am going to write some code for the arduino that allows to change any signal parameter easily from a graphical interface running on pc..
It should be easier to find the correct settings if I could adjust them by simple clicking, instead of having to upload new code for every change.
Goal would be to have code that hopefully will work with any transmitter.
..this will take some time, there's other things to do, too..

I found a dealer who is selling Nine Eagles trainer cables..
I will get one and check which pins should be connected.
Might be I'll have to put in a resistor, although I thought it works on rising / falling not on voltage levels.
The voltage coming from the arduinoboard is 5V and as described above the transmitter produces a 3V signal between pins 1+2
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Old Sep 02, 2010, 08:36 AM
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i think thats the same as a s-video connector!

the timing thing is usually a set it one time and forget it ordeal. not really worthy of developing a menu for imo.

btw, i got mine sorted! arduino generated ppm seems to be working fine with the spektrum dm9 for JR at 22ms.
-sj
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Old Sep 04, 2010, 12:52 PM
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it is an s-video connector, true.. but I am pretty sure, a simple s-video cable won't work. I want to order an original cable so that I can check how it should be wired.

You're right, a menu is not neccessary, but I do hope it will help me to find the correct timings, the ideas are already in my head.. just need to find some time to develop the interface, the menu itself won't be too much work.

Will the transmitter sync itself to the incoming PPM signal, or are there any sync pulses that the arduino should sync to?
I tried so many timings and none of them worked. Maybe I should record the signal again.
The shuttering occurs only until I push the trainer switch, then it stops.
How does a trainer connection work usually?

I bind one transmitter to the heli, that will be the pupil tx, correct?
then I connect the cable to both transmitters and the pupil keeps control until the trainer pushes it's trainer switch? ..or will the pupil push the switch?

I am not sure about this, since pushing the switch and controlling the sticks at the same time is quite tricky, in this case a real switch that doesn't need to be pushed would be much more comfortable.. the manual says for trainer control the switch has to be held..
But as mentioned, when I connect my generated signal to the tx, servos start to shutter, as soon as I push the trainer switch, shuttering stops and the tx looses binding to the heli, after releasing the switch they bind again..

Could this mean, that the trainer uses it's own HF-module and the trainer cable won't be used to transfer the PPM signal? In this case the PPM signal would only be usable for the simulator cable.
But in this case I don't understand why the servo start shuttering..

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Old Sep 04, 2010, 01:27 PM
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I recorded the signal again.. it looks like they don't use a standard PPM signal.

the long sync pulse is ALWAYS 21 ms. Both with min and max positions.
This is different to everything I read about PPM signals until now. I'll put this into my code and try again, strange..
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Old Sep 04, 2010, 03:14 PM
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..no success

the PPM signal that comes from the transmitter is between 1+2 and also 1+3.
Even between 1+4 there is a slight signal that has 5 pulses and a long break between. It comes nowhere near the voltage of the others, but it is cleary not normal noise. maybe some crosstalk..

I assume when I connect my signal to the tx it interferes with the transmitters own signal, therefore the shuttering.
I rechecked which pins I have to connect, to make the servos shutter, it's 1+3. When I connect to 3+4 there is no reaction.

Any ideas why there is 0.3V between 5+1 ? when the trainer switch is pushed it goes down to 0.0V..

I think this is going to be much more than only generating a PPM-signal that could be connected to an input port. Maybe the transmitters checks by the 0.3V if another transmitter is connected, especially the same (or at least really compatible).
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