View Full Version : Metal detecting circuits

08-06-2005, 12:43 PM
Hi friends,
Am searching for a metal detecting circuit. I found some on the net. Most prefer to use coils but they dont give the proper dimensions . Have anyone of u worked with metal detecting circuits (especially iron). If anyone of u could give me some info in this area it would be useful. Also if anyone can suggest me some ICs that could be used instead of the coils it would be really great. I found some circuits using ICs but those ICs are not available.

Thanks in advance,

09-20-2006, 08:02 AM
same case here ,waiting for the replies !!

10-15-2006, 11:11 PM
maybe you can pun SMT coil under you device ?

10-19-2006, 09:01 PM
i think you shiud use SMD coils

10-20-2006, 11:45 PM
Metal Detectors work on the principles of Induction and level of current through a coil at resonance.

All you need is an oscillator and a receiving coil, mutually coupled in air.

The reciving coil will change its resonant frequency due to varying L and/ or C. All capacitance (in Series or Parallel Resonant circuits) are the result of the capacitance due to the physical (and calculated !! :wink: ) component capacitor + capacitance between the windings of the physical inductor + the stray capacitance due to the physical proximity of the inductor to nearby "ground" objects, components etc., Any change in the capacitance / inductance value will change the "Q" as well as the resonant Freq. of the LC tuned circuit. Iron will increase the inductance and brass will decrease the inductance, in proximit with a current carrying coil.

Current is maximum, off resonance and minimum @ resonance, depending upon the configuaration and status of the Tuned circuit ( Osc, tank, Receiver tank, RF amp, series or parallel Tuned circuit...)

It is then easy to build a Osc./ Receiver pair and measure the Current through OR Freq. of these tuned circuits. Any stray capacitance- a hand, metal etc., will change the resonant freq. and current in the coils.

SMD inductance is not necessary, as any metal detector circuit must work at some distance from the coils. This usually calls for coils of large diameter to cover area as well as distance.

:arrow: The ICs used are just oscillators or amplifiers. Even a 555 timer Ic can be used :lol: :lol:

10-21-2006, 01:29 AM
i mean surface mount coils, made of thin wire... inner hdd wire - that is the example )

10-22-2006, 09:18 AM
Hi dmage!
I dont quite understand??
Do you mean the SMD coil of the HDD head actuator??

The coils used for Metal detection are usually air-cored around 3" and more diameter.

10-22-2006, 07:52 PM
yea. aircored. im also think so.
surface mount... i mean the coil should be flat and consist of
some turns of the wire ... mm... only one layer maybe...

10-23-2006, 05:36 PM
i think for robots use of bfo type is not good beacouse of low sensitivity in sertain medium
i suggest to go for induction balance metal detector by john clarke (try google)* for the ckt i have tryed it its giving 6cm in air medium