BFO Metal Detector ..

Thread Starter

super

Joined Dec 21, 2015
2
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 ?
 

bertus

Joined Apr 5, 2008
20,314
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
 

alfacliff

Joined Dec 13, 2013
2,458
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.
 

jjw

Joined Dec 24, 2013
508
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.
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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