555 timer metal detector

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Instead of a 10 mH coil, use a larger flat coil, like 50 turns of 0.5 mm dia.wire would on at least 6" diameter, in a tight strain. Detecting metals requires to affect the coil inductance by a larger metal mass. Using a small coil might only detect a magnet if it affects coil iron core.
Better metal detectors use larger coils, also the beat-frequency principle for a good sensitivity.
 
Thank you for your reply. can you please give me some details on how to implement the BFO principle using 555 timer.
 

Is there any way of increasing the efficient distance sensing without increasing
the diameter of the coil? I tried various things, such as increasing the induction to 100mH
and different caps with no success.
Amitai
 

amitaiwe said:
Is there any way of increasing the efficient distance sensing without increasing
the diameter of the coil? I tried various things, such as increasing the induction to 100mH
and different caps with no success.
Amitai
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In a metal detector, a flat large coil is preferred as its magnetic field is spread over a wider area. A small coil can help to detect close objects only.
I would suggest you to google metal detectors and see how it is done.
The beat-frequency method uses two or more coils overlapping, and adjusted so that the beat from two oscillators feeding two coils is rejected like in a bridge system. Then presence of a metal object mis-balances the system and the beat frequency is heard. This system also allows to vary the frequency of one oscillator, so the varying pitch helps to approach a hidden object.
 
Why are you suggesting the BFO method? Is that butter then a PI or VLF (in distance maximizing terms) ?
 

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