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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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  1. HANKMARS

    HANKMARS

    75
    9
    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
     
  2. HANKMARS

    HANKMARS

    75
    9
    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

    nimiq

    8
    2
    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:
    https://en.wikipedia.org/wiki/Radio-controlled_model
    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
    Roger
     
    HANKMARS likes this.
  4. HANKMARS

    HANKMARS

    75
    9
    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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