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Does this coding look familiar to anyone? RC transmitter

Discussion in 'Radio and Wireless' started by HANKMARS, Mar 19, 2020.

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    Jul 28, 2019
    The "carrier" waveform is a square wave at 14Hz. The embedded coded waveform is a variable pulse width square wave running at 300Hz. 1.1.JPG DSCF2525 (2).JPG DSCF2527 (2).JPG DSCF2531 (2).JPG


    Jul 28, 2019
    The transmitter in this case is from a Chamberlain (Sears) garage door opener from around 1980. When a signal was sent from this transmitter, what I found on the receiver board was a little "burp" on the output of the op-amp that resided on the receiver board. The output voltage would stutter for about a half second then jump to 1.5 volt above its quiescence level for another half second. This was enough of a signal to condition and update the logic circuit in the gate opener unit that I constructed. I am still curious as to what the "official" signal was out of the receiver circuit and how it was differentiated from the other possible 143 signals.
  3. nimiq


    Jun 30, 2019
    Hello Hankmars

    The waveform reminds me of my old radio control model digital proportional transmitter modulation - the wider low period was used for synchronising. Each pulse after was passed to a servo. Each high pulse width was varied through the transmitter joysticks (varied between 1 to 2ms) and set the servo position ie the elevator, motor, rudder position etc. Repetition rate was around 50Hz. This describes in better detail:
    Are there any IC's identifiable in say the receiver - maybe searching on their part number will bring up useful datasheets.
    Hope there's a clue somewhere for you, happy hunting
    HANKMARS likes this.


    Jul 28, 2019
    I did take some IC numbers from what appeared to be a Tx and Rx set. One each located on their respective board. I think it was the Tx component data sheet that I found, or it may have merely a chip for sale. A little vague on the memory.
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