BFO Metal Detector ..

Discussion in 'The Projects Forum' started by super, Dec 21, 2015.

  1. super

    Thread Starter New Member

    Dec 21, 2015
    2
    0
    hello ^^

    i'm working on this video ....
    The buzzer is continuously beeping even with no metal near the coil and even without the two coils XD
    what should i do ?
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,155
    772
    If you want it to stop buzzing...
    Option 1) remove the battery.
    Option 2) remove the buzzer.

    Or

    Post the circuit diagram for further assistance....
     
    ebeowulf17 likes this.
  3. bertus

    Administrator

    Apr 5, 2008
    15,805
    2,389
    Hello,

    Please post the schematic.
    Also at wich frequency do the oscillators work?
    RF and a breadboard are not a good combination.
    The strips inside the breadborad will make capacitors that will influence the working.

    Bertus
     
  4. super

    Thread Starter New Member

    Dec 21, 2015
    2
    0
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    bfo types require that the frequencies of the two oscilators be the same. there are no trimmer caps on that circuit to vary one to "ballance" the circuit. they work by changing the inductance of the search coil with the burried metal, changing its frequency a bit, causing a hetrodyne that is amplified by the rest of the circuit.
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,805
    2,389
    Hello,

    It looks like the circuit in this link:
    http://chemelec.com/Projects/BFO/BFO.htm
    Here is info on the used PCB, from that site:
    http://chemelec.com/Projects/BFO/BFO-3.jpg
    You can see there is a fixed coil (220 μH) in the picture and a would coil as receiver coil.
    The coils must have about the same inductance to have the circuit working.
    When they are to far off the speaker will keep a beep tone.

    Bertus
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,976
    1,136
    Option 3) remove the phone (which contains metal).
     
    Dodgydave likes this.
  8. jjw

    Member

    Dec 24, 2013
    174
    32
    In the home page of this circuit they say that the second coil is trimmed with a brass nut around the coil.
     
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