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Frequency Detector

Discussion in 'General Electronics Discussion' started by Unthoughtof, Mar 4, 2014.

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  1. Unthoughtof

    Unthoughtof

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    Mar 4, 2014
    Hi I am working on a project for school and I am running into problems. The project uses a transmitter and receiver to operate. I am putting a set frequency into the transmitter and getting the same frequency on the receiver end. What i need now is a circuit that can detect a set frequency and then activate a relay to operate a motor. Any help would be greatly appreciated!
     
  2. duke37

    duke37

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    769
    Jan 9, 2011
    You will need to make a circuit to tune to the incoming frequency. In olden times, a circuit made with an inductor and capacitor was used. Nowadays an amplifier is used to eliminate the inductor. You will need to know the frequency to calculate the components.

    Once the tone has been detected, it can turn on a transistor which will activate the relay.

    Inforrmation you need :-
    Power supply details
    Frequency
    Op-amp details
    Relay details
     
  3. Unthoughtof

    Unthoughtof

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    Mar 4, 2014
    Thank you for the reply. I am using a 555 timer to generate my frequency. So i know the frequency that is coming out, the only thing i need is where to start as far as the detection circuit, i am trying to use a 567 but not having much luck.
     
  4. Arouse1973

    Arouse1973 Adam

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    1,081
    Dec 18, 2013
    Can you post the circuit diagram and the PCB if you have one.
    Adam
     
  5. Externet

    Externet

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    Aug 24, 2009
    The NE567 works very well and reliable, for sinewaves. A 555 outputs square or triangle waves and will not yield a very stable detection.

    I have not found a monolithic sinewave generator IC. Somehow they are not built. It would be nice to set a capacitor and variable potentiometer on a chip pins, at 555 style and get a clean oscillator. Alittle more complex IC that does it is the ICL8038
     
    Last edited: Mar 4, 2014
  6. duke37

    duke37

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    Jan 9, 2011
    The 8038, will generate a reasonable approximation to a sine wave and is tunable.
    If you do not want to vary the frequency of the tone, you could put a filter after the 555 or before the 567. The 567 is a phase locked loop with two detectors. One or the other should work on non sine waves.
     
  7. Unthoughtof

    Unthoughtof

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    Mar 4, 2014
    So if I can convert the Square wave coming out of the 555 into a sinewave then the 567 will be able to detect that better ?
     
  8. duke37

    duke37

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    769
    Jan 9, 2011
    Obviously, the cleaner the signal into the 567 the better.
    It is a long time since I read up about the 567 but I remember that one of detectors will lock onto harmonics. This you do not want. I suggest that you chose the best detector for your purposes.
     
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