A Very Simple "Beat Frequency Oscillator" type of Metal Detector.
These are about the Simplest of all Metal Detector types,
But still quite useful for many Detecting applications.
And although this one is particularly simple, I find it works very well.

For use outside on the ground the coil "MUST have a Faraday Shield",
or it will not be of any use because of Ground Effects.

Note: If there is Enough Interest in this Project, I will create a PCB for it and
Elaborate on the coil Construction. But for now, Only the Schematic is Presented here.

L1 is a Standard RF Choke. My choke was made by "Delivan", and I can supply them if needed.
But any simular choke should be OK.

Depending on the Accuracy of the Inductance of L1 and how close the
Inductance of L2 comes out, you may need to add or remove a turn or
so to get both oscillators operating at the same frequency.

As an Alternative to adding or Removing Turns, You can wind the coil with
Various Taps, starting at 25 turns, than 26 turns, 27 turns and 28 turns.
Than Pick the tap that works Best.

L1 could be an adjustable choke with slug tuning.
Or the parallel 470pf cap to L1 could be replaced with a Variable AM Radio,
Tuning Capacitor of 365pf.
Thus eliminating the need for the 10K pot.

But I found the 470pf and 10K Pot Arrangement, Quite Simple and Satisfactory.

My Proto, Built on a "Bread Board", Detects a Canadian Quarter at about 5 inches in Air.



"Back to my Projects Page"




 My BFO Detector Schematic.

 BFO Detector PCB.
          This is Under Construction.

 BFO Detector Coil.
          This is Under Construction.