BFO metal detector #2

Design

• Simple design using readily available components.

• Easy to build and set up.

• Light weight suitable for portable operation.

• Low power consumption suitable for battery operation.

• A small and compact design.

Circuit description

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

applications. This detector will be found to be a little more sensitive than BFO metal detector No1, and has a greater audio output capability easily able to drive

either a  pair of headphone or a standard 8ohm loudspeaker of the type often found in small portable transistor radio's.

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 it may be found necessary 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. However as L1 is variable there should be enough room for adjustment here without the need for altering the search coil (L1).

Possible alterations

Components R1, R2, D1, and C1 could be replaced with a Variable AM Radio, tuning capacitor of 365pf, however this would require either adaptation of the existing PCB or alterations to the PCB design.

Transistors Q1 and Q2, there are many possible substitutes which could be used in place of the 2N3904's, e.g. BC182's, BC547's to name but a couple.

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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