BFO metal detector

Discussion in 'Homework Help' started by kriti gupta, Dec 8, 2014.

  1. kriti gupta

    Thread Starter New Member

    Dec 8, 2014
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    Hello, I need help with this circuit.
    I understand the overall working of the detector but I do not understand the working of the circuit components and their roles.
    Thank you for the help!
     
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  2. kriti gupta

    Thread Starter New Member

    Dec 8, 2014
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    The buzzer is continuously beeping even with no metal near the coil. Adjusting the variable resistor didn't help.
    With the metal near the coil, there is no variation in the tone of the buzzer.
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    you should add dots to all points at which you have made connections on the schematic then re-post it. the drawing you posted is confusing about where some components are connected and where the lines cross but do not connect. i suspect this is where you have a problem.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    it appears to be an old style bfo detector, it uses an am radio station as a reference, tuning the pot to "zero beat" the carrier of the oscilator with the radio station. when metal enters the field of influence of the coil, the oscilator is detuned and the mixed signal sets off the buzzer.
     
  5. kriti gupta

    Thread Starter New Member

    Dec 8, 2014
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    I used a vegakit with a pcb to make it, so the connections should be right, I guess. Here's the circuit again.
     
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  6. kriti gupta

    Thread Starter New Member

    Dec 8, 2014
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    I found the basic mechanism on the internet, I do not understand the contributions of the individual circuit elements.
    Also, There were 58k resistors available instead of 56k, could it be because of this that the circuit is failing?
     
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