G4USP

Page last updated: 28/09/2012

 

BFO metal detector #1

 

Design

 

Circuit description:

A very simple "Beat Frequency Oscillator" type metal detector built entirely from discrete components. These are one the simplest of all metal detector types, but still
quite useful for many detecting applications. 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.

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.

Happy hunting...

 

 

        BFO metal detector schematic:

        BFO metal detector component placement / layout:

          BFO metal detector PCB bottom trace:

 

Original Files:

    Further to the details of the pages above - the original CAD files created using EAGLE PCB Design software are included below, along with associated PDF files of both schematics and PCB layouts suitable for printing directly.

    To use the original CAD files, they must be opened with EAGLE. Visit the CADsoft web site for more details, the software (including a freeware version), part libraries, tutorials, for EAGLE are available.

    BFO metal detector schematic PDF

    BFO metal detector PCB component layout PDF

    BFO metal detector PCB bottom track layout PDF

    BFO metal detector EAGLE schematic

    BFO metal detector EAGLE board

 

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