Radio control remote reverse engineer

Discussion in 'The Projects Forum' started by tazit, Apr 2, 2009.

  1. tazit

    Thread Starter New Member

    Apr 2, 2009
    I have bought an used rc remote wich should work at 27Mhz. I want to use it for a robot I am planning to build.

    Firstly I want to see if the remote works and if so how the signal is modulated. How could I do this? (I was thinking about connecting the antenna of the to an oscilloscope but I'm not sure this would work)

    Any ideeas sugestions are greatly appreciated.
    Thank you!
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    What did the remote normally control?

    Control type:
    "Analog" = Variable position aka "proportional.
    "Digital" = on or off. Not referring to PCM Digital control.

    How many functions does it have? Exmple, for a car, 4 channel: steering - analog, throttle -usually analog, brake - digital, reverse- usually analog.

    For an airplane: 6 Channels: Ailerons, Elevator, Rudder, Throttle (Primary 4), Flaps & Landing Gear - Digital (although variable flaps are common also)

    The $10 R/C Cars are usually all "digital", so easier to modify. Chop off the wires that normally go to the motors after measuring the outputs, and do whatever voltage level shifting and smoothing needs to be done to function in new application.
  3. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    To find its modulation pattern you need a spectrum analyzer.. Oscilloscope based analysis is not easy on RF... I was on such plans some time back but couldnt build the appropriate reciever circuit and was finally compelled to use its original reciever chip and components.. You can hack into motor wires as stated in the previous post and will get abt 5v for high..
  4. DickCappels


    Aug 21, 2008
    Yes, you can connect the antenna to an oscilloscope, and you may well learn something about the signal if you scope has sufficient bandwidth.

    As a precaution, use a 10X probe, just in case the voltage at the point you connect the probe is high -you wouldn't want to hurt the scope's input stage. And besides, you may need the 10X probe to get sufficient bandwidth.

    A few months ago, did something similar with a 330 Mhz remote control transmitter, so I made a diode detector and captured the pulse train coming out of that.

    You can use a circuit like the one below to detect the signal. The R and C will give you about 100 kHz bandwidth for the detected signal, but will drop to about 50 kHz with a 10X probe connected to the output.

    If you don't have a radio frequency choke, you can use a resistor instead, with a significant loss in sensitivity. Or, you can omit the choke and the antenna and connect the ground to the negative battery terminal in the transmitter and the anode directly to the antenna (assuming its a low power transmitter). Again, use a 10X probe to protect your scope.