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I have found bunch of information about how to hack an RC car with a PCB; and how to control an Arduino from a receiver. Also how to run a servo from an Arduino, but I'm looking for a way to make an Arduino send signals to a 27 MHz 3 channel receiver, Using three potentiometers to decide servo location.

Is there any information about this somewhere? - I have an old transmitter lying around if needed.

Links, pointers - anything is welcome.

[It does not have to be 27 MHz AM, it is just what I have on the shelve, without investing in new gear]

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    Ironically, your cleanest solutions might be to get a toy using an off-the-shelf 2.4 GHz chipset with a protocol that has been reverse engineered (which is to say, almost anything on 2.4 GHz that has been on the market for more than a few months) and just drive it by hanging an appropriate module for that chipset off the arduino, setting the original TX aside. – Chris Stratton Sep 8 '14 at 18:59
  • SO, what you suggest if i may "clean it up" a bit, is that i go and invest in an X-Bee shield and an RC receiever with 2.4ghz signal. If so - Is there any suggestions on how to make this work, in terms of existing arduino code? – Magic-Mouse Sep 10 '14 at 6:36
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    No, I would not use an XBEE. Take a look on rc sites and see the various 2.4 GHz chips commonly used (most are symmetric in that the same chip is used for transmitter and receiver, regardless if there is or isn't "telemetry" from the model back to the controller). You will probably find that people already have arduino code for driving them. – Chris Stratton Sep 10 '14 at 15:52
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The easiest way would be to open up the transmitter, desolder the potentiometer used for the stick and solder the cables to Arduino's PWM instead. Then use analogWrite() to simulate stick position. If your TX would use that potentiometer with more than 5 V, you'll not able to use full ppm values. A RC or a RCL filter may be needed between PWM output and RC input to "smooth" the PWM into an analog signal. There are a lot of online calculator to find good R, C and L to polish your signal.

This assuming your TX is using potentiometer like stick; if it is a really cheap one, it may be using buttons. If this is the case, then you connect a transistor in parallel with the button, that way you can keep manual button.

Another way is to program your Arduino to look for ppm signal (normally 50 Hz with high starting value with a period from 500 to 2000 µs) and then look for this signal into the Tx PCB; if found cut the trace of the generator and solder your cable from Arduino. I've seen around a lot of libraries outputting ppm (they are used on drones to mix single ppm channel back to PPM to use only one pin from logic board without having to hack standard RX

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    Please explain how one would control the transmitter with the Arduino. That's basically the whole point of this question... – sachleen Sep 8 '14 at 17:53
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    Edited to be more clear. Just emulate potentiometer output with a pwm output. – Lesto Sep 8 '14 at 17:58
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    This is unlikely to work without at least filtering, as both devices are varying over time - the Arduino is not outputting an analog signal but something that averages to one, and the transmitter is not measuring the potentiometer voltage continuously but rather comparing a sawtooth to it or reading it with an ADC about 50 times a second. – Chris Stratton Sep 8 '14 at 18:58
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    @ChrisStratton even if arduino pwm is by default at 200hz, problem you described may rise. Added rc and rcl filter. Also added direct injection of ppm signal – Lesto Sep 8 '14 at 22:39
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    Interesting. You're assuming that the pot is wired into a voltage divider, and suggesting cutting the trace on the output of the voltage divider and feeding that trace with a filtered PWM output from the Arduino instead? – Duncan C Sep 9 '14 at 0:19
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Consider the methods of US patent 9,996,079 (linked URL):

"Radio frequency device detection and intervention": US 20180081354 A1

After reverse engineering the badly written descriptive, you should be able to come up with an Arduino board set.

P.S. Try not to copy the whole patent.

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Many RC TX have a remote connector where you can input the signal and not having to open them.

In any case, 27 MHz RC are a train of pulses, of variable width, from 2 to 20 ms each, one for each channel, flowed by a 20 ms pause.

This can be recreated in a single output pin.

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  • Such a signal may well exist internally, yes. But 27 MHz gear tends to be the extreme low end of the market, and unlikely to expose the signal on a trainer or "buddy box" connector, so some internal probing/investigation/modification would be required. – Chris Stratton Sep 8 '14 at 18:56

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