Ultra High Sensitivity Metal Detector Circuit

  
This circuit is a metal detector capable of detecting large metallic objects. at a depth of 2m to 3m. It depends on the size of the object, and often on the type of soil. Construction is very easy to implement even for a beginner. The necessary components are easy to find everywhere. This detector has the ability to detect a gold coin of 20mm and a thickness of 1.5mm and a depth of 90cm. The two present frequencies are the one that is generated by the circuit and the one that is returning for comparison. By placing the coil near a metallic object the returning frequency is changed. Those two frequencies are the subject of comparison by our circuit. At modern metal detectors, the reference generator operates at a frequency that has different magnitude from that which appears in the field of the search coil.
Ultra High Sensitivity Metal Detector Circuit - schematic

How the circuit works

The circuit uses the IC1 which is the CD4011 and the IC2, the CD4023, both of these are logic ICs. The reference generator is implemented in two logic elements of the integrated circuit IC2. Its frequency is stabilized and is determined by the quartz crystal X which is 1MHz. The generator with a variable frequency is made on the first two elements of the IC1. The oscillating circuit here is formed by the search coil L, the capacitors and the varicap. The potentiometer 10K is for tuning to a frequency of 100kHz, this actually sets the required voltage to the varicap VD1.

The circuit use the signal logic elements IC1-3 and IC2-3 as buffer amplifiers and the signal mixer is the IC1-4. The speaker should be a high resistance phone capsule. And the capacitor C10 is used as a shunt capacitor for the high frequency coming from the mixer.

The metal detector circuit is powered by a 9V DC battery or you can use 6 AA batteries for much longer working times. The capacitors C8 and C9 work as a filter. The search coil requires special precision and attention in its construction. 

It should be wound on a plastic tube with an external diameter of 20cm. The coil should contain 100 turns of 0.3mm wire. When the winding of the coil is completed, it should be wrapped in aluminum foil to create an electrostatic shield (this will reduce the effect of the capacitance between the coil and ground). It is important not to allow electrical contact between the winding wire and the foil. The aluminum foil itself should be protected from physical damage, so it should be wounded well with an insulating tape. Then you should secure the coil in a water proof hard casing, to protect it from damaging it and to get wet.

The diameter of the coil can be different than 20cm. But the smaller the coil, the more sensitive the circuit becomes, but the area of ​​searching for hidden metal objects narrows. When the diameter of the coil is increased, the same effect is reversed.

Having located the search coil close to the ground surface, adjust the detector with the potentiometer. And so that in the speaker capsule the sound is almost none. Now you are ready to use it and search. If a metallic object will be in the range of the coil the sound will get loud. 

Update: Missing resistor value R = 150KΩ.





Leave Comment

characters left:

Ann   Nov 5, 2017

can I use 12v battery??

diakoooo   Oct 3, 2017

i very need helpe Does the circuit work for you? I checked all the parts and paths Everyone is healthy But there is no voltage across the coil Is zero please guide me

Mahmut   Oct 1, 2017

4.7uf/16V is electrolytic capacitor. Positive goes down and negative up, as you see it.

Antonio Empleo   Oct 1, 2017

4.7uf capacitor,,it is polarized caps but in the shematic is non polarized symbol ,, i was confused,,, please help me thank you

Roberto   Sep 23, 2017

Mine is working fine! Check your components polarities and check if any IC is burned. Make a coil 40cm diameter 50 turns same capacitor and you can search much deeper ;-)

diakoooo   Sep 23, 2017

I built this circuit But it does not work Does anyone have this problem? please help

Picture of the coil?   Sep 6, 2017

A picture of the hand made search coil would be very helpful.

manu   Aug 19, 2017

Is there any video. Thank you very much. The capacitor of 4,7uF whould'n be electrolitic? There isn't any capacitor non electrolitic whitch that capacity.

Yo   Aug 19, 2017

Resistor ¿R ?

jordan   Aug 18, 2017

can you send the schematic diagram?

Boby   Aug 16, 2017

I correct it, its 150KΩ. Sorry for the confusion.

Nick   Aug 16, 2017

What resistor has to be placed at the "R" in the scheme ?

albano   Aug 8, 2017

Can send PCB, ultra-sensitive detector scheme?

cheikh   Jul 25, 2017

Thank you very much. but what about L*

New Circuits

.