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Various metal detector circuit diagrams

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ppopular electronics magazine metal detector

Twin Loop Treasure Seeker

by Robert and David Crone

This pulse induction metal detector utilizes a dual-loop search coil for canceling ground effects and RF interference. It was published in the September, 1989 issue of ETI, a popular electronics magazine that is owned by UK publisher Wimbourne Publishing, Ltd.
 
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Sandbanks
by P.J. Wales
The Sandbanks is one of the earliest pulse induction metal detector projects, and is often the basis for other designs and projects. It was published in the January, 1979 issue of Practical Wireless, a ham radio magazine that is owned by UK publisher PW Publishing, Ltd. Later revisions were published in the April and August issues, and I have made the necessary corrections to the schematics.
 
deep seeker metal detector diy

Coil Winder

by Carl Moreland

This is purely a woodworking project for those who are looking for a more automated way to make coils. It's not motorized, but it is fully adjustable to any coil size (my prototype does 3-24 inches) and it has a counter. Cost of construction is less than if you use scrap wood and find a surplus counter. For those who are really agressive, consider an electronic counter and a motor drive, perhaps using a stepper motor programmed to stop at a certain count.
 
ee pulse induction

The circuit described here is that of a metal detector. The opera- tion of the circuit is based on superheterodyning principle which is commonly used in superhet receivers. The circuit utilises two RF oscillators. The frequencies of both oscillators are fixed at 5.5 MHz. The first RF oscillator comprises transistor T1 (BF 494) and a 5.5MHz ceramic filter commonly used in TV sound-IF section. The second oscillator is a Colpitt’s oscillator realised with the help of transistor T3 (BF494) and inductor L1 (whose construction details follow) shunted by trimmer capacitor VC1. These two oscillators’ frequencies (say Fx and Fy) are mixed in the mixer transistor T2 (another BF 494) and the difference or the beat frequency (Fx-Fy) output from collector of transistor T2 is connected to detector stage comprising diodes D1 and D2 (both OA 79). The output is a pulsating DC which is passed through a low-pass filter realised with the help of a 10k resistor R12 and two 15nF capacitors C6 and C10. It is then passed to AF amplifier IC1 (2822M) via volume control VR1 and the output is fed to an 8-ohm/1W speaker. The inductor L1 can be constructed using 15 turns of 25SWG wire on a 10cm (4-inch) diameter air-core former and then cementing it with insulating varnish. For proper operation of the circuit it is critical that frequencies of both the oscillators are the same so as to obtain zero beat in the absence of any metal in the near vicinity of the circuit. The alignment of oscillator 2 (to match oscillator 1 frequency) can be done with the help of trimmer capacitor VC1. When the two frequencies are equal, the beat frequency is zero, i.e. beat frquency=Fx-Fy=0, and thus there is no sound from the loudspeaker. When search coil L1 passes over metal, the metal changes its inductance, thereby changing the second oscillator’s frequency. So now Fx-Fy is not zero and the loudspeaker sounds. Thus one is able to detect presence of metal
 
metal detector

Hi,

Any recomendation for advanced metal detector but simple yet for DIY?

TR2000
 

Re: metal detector

Other good places to find complete design of metal detectors are patents.
And metals may also be detected using magnetometers, two box detectors etc.
 
Is it just me or has anybody else noticed that all these designs are many years old. It seems strange that they rely on RC network or monostables to create delays and pulses. Perhaps there isn't enough enthusiasm to produce new designs but I would have thought that almost all the circuitry in the designs listed could be greatly simplified by using a cheap micro to do all the timing functions.

Brian.
 
yes these are old designs from 70s or 80s.
but I've seen some designs (rare) with a pic or 2 ...
does all the metal searching method have not evolved since the 80s ?
 

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