DIY TX module from other transmitter..?

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DIY TX module from other transmitter..?

Postby John_Edward » Thu Jan 26, 2012 10:36 am

So, as I have bought a few RTF sets, I now have couple IR transmitters, an FM transmitter, and two 2.4GHz transmitters.
I also have a TGY9X with the internal DIY FrSky module.
It would be great if I could ditch all the crappy TXs and use my TGY9X to control everything, but as most of the models are micro or mini in size with integrated RXs, changing the RX to for example the V8R4 is not possible.
With some models it might be possible to use the SuperMicro 2.4GHz module and RXs, but that is an expensive solution I really don't want to do.

So the only feasible way is to keep the model intact, and control the original RX with my TGY9X.
Of course, one could just rig a bunch of servos to move the transmitter sticks, but I'm kinda thinking about a more sophisticated way ;)

I'm sacrificing my Syma S110's IR RX first, as the model itself is crap, but the TXs PCB is tiny (S107G for the win!):
3CH mode 4 - Throttle on Left Y, Elevator on right Y, Rudder on right X.
Power: 6xAA = 7.2v to 9v, fed to a 5V regulator
All of the controls are 4.7K potentiometers, with throttle being from 0 to 4.7k, Ele and Rud are 0 Left/Backwards, 2,3k middle, 4.7k Right/Forward.

So, this here is the first idea
:
TGY9X ))) V8R4--[x]--TX ))) RX
The [x] here is simple in idea, a circuit that takes the servo PWM data and changes that to a "simulated potentiometer", a DC signal between 0 and 5v.
This is then fed straight in to the pins the TX had its potentiometer.
Pretty easy to do with an Arduino, but I'm not sure how fast it would be.
Using the FrSky RX will make it simpler, as it has dedicated channels, so I don't have to play with the PPM signal from the transmitter.
It could be possible to go through the trainer port, read the PPM data and convert that straight to the IR controls, but the IR data isn't the worlds simplest thing to replicate, so maybe someday.

Now, this is what I thought up one sleepless night.
Someone might have, and probably has, done this much better, if so, information would be nice :)
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Re: DIY TX module from other transmitter..?

Postby chrisjunkie » Thu Jan 26, 2012 9:11 pm

Could you not just hook them up via the trainer port to the original remotes? Bit of a bulky solution but easy to do :-)
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Re: DIY TX module from other transmitter..?

Postby ergocentric » Fri Jan 27, 2012 7:08 pm

John_Edward wrote:the controls are 4.7K potentiometers, with throttle being from 0 to 4.7k, Ele and Rud are 0 Left/Backwards, 2,3k middle, 4.7k Right/Forward.


1. I find it unlikely that you would use the full stroke of the pot (270°) for a control, so more like 1.5k min to 3k max (90°)
2. have you looked at electronic potentiometers with a microcontroller like an arduino to decode the t9x?

Image
http://electroschematics.com/803/digital-potentiometer/
http://electroschematics.com/3035/elect ... r-circuit/

if you can reverse engineer the IR tx design, maybe all you need is an adjustable voltage derived from your servo (or trainer port) signal
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Re: DIY TX module from other transmitter..?

Postby ergocentric » Fri Jan 27, 2012 7:16 pm

note digital pots have very few steps (usually only 32) so your controls will not be smooth, and with all the chicanery you may be noticing a lag in the controls
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Re: DIY TX module from other transmitter..?

Postby Old Crock » Sun Jan 29, 2012 12:25 pm

If you Google around a bit, you will see that you can get Quad Digital Pots with 256 positions.
I used one long ago to make an interface from a Tx to the Joystick port on a PC for the FMS simulator. Worked like a bomb.
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Re: DIY TX module from other transmitter..?

Postby John_Edward » Wed Feb 01, 2012 2:07 am

Well, a little status report with this project:
I got sidetracked when I got stuck with the potentiometer problem (expensive and crappy availability here) and went with a fully custom made transmitter for this particular heli.
So, Using my arduino as a Logic Analyzer,I spend a night decoding the IR signal my little 3CH heli used and got pretty far, but then I stumbled across IRrc and IRheli.
It has all of the dirty work done already, so I could concentrate on the hardware.

The result, is in my opinion, quite nice!
A fully stand-alone, Arduino powered IR transmitter module that fits in the old Turnigy 9X TX module shell.
The IR LED bar is still a prototype, but it is already much more powerful than the one in the old transmitter.

The arduino reads the PPM signal coming from the controller, translates those to the protocol used by the heli with IRheli, and then transmits them.
It still has a few problems, like the fact that I don't do any safety checks.
So even tough ER9X doesn't allow the 2.4GHz module to transmit if I start the controller with full thrust, the PPM signal is still there for my trigger happy arduino ;)
The original controller refuses the start transmitting if the throttle isn't off when it is turned on, and even if it is, it requires you to set the thrust to 100 and then back to 0.
I'll have to document, polish and add some safety to this a little more, and then I'm going to release the plans and such.

And the cost of parts was really low.
The only part that really costs anything is the 'standalone arduino', ie. Atmega328, a 16MHz crystal, 5V regulator and some caps.
Other than that, there is just one BC547 and a 880ohm resistor for driving the IR leds.
So , if you already have an Arduino board, it just takes some time and under 10€ in parts, most of which you can scavenge from the IR original transmitter!


And yes, my M3 heli (Syma S107G rebrand) is really, really nice to fly now <3
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