Many radio amateurs dream of assembling a simple metal detector with their own hands to search for treasures. In my childhood, I also had such a dream, to find a huge wooden chest with treasure. And so I decided to implement it. Today I will tell you how to make a simple metal detector using two NE555 microcircuits. The device operates on the principle of induction balance, consists of two generators operating at the same frequency, designed to search for ferrous and non-ferrous metals without discrimination. The metal detector has good sensitivity, it is able to detect a five-ruble coin at a depth of fifteen centimeters, larger objects up to eighty centimeters.

This figure shows a diagram of a metal detector based on two NE555 microcircuits.

Simple metal detector on two NE555 microcircuits

Download metal detector diagram 

And this is the printed circuit board of the metal detector.

The principle of operation of the metal detector is very simple, two generators operating at the same frequency, make up a single balanced, induction system that works on the verge of failure. As soon as metal enters the range of the coils, the induction balance is disturbed and a signal is heard in the dynamics.

The metal detector’s coils must be exactly the same. Each coil is wound separately on a 19 cm diameter rim and contains 30 turns of 0.5 – 0.7 mm wire in varnish insulation.
For winding the coils, I used a PETV-2 winding wire d = 0.5 mm, I pulled it out of the old transformer, and used a pan of a suitable diameter as a frame. He fastened the coils in six places with a strong thread, then impregnated them with bakelite varnish and wrapped them with electrical tape.

After all components have been soldered, the device must be properly configured. Resistor P1 for 100K is designed to adjust the frequency of the receiving generator. Resistor P2 200K for coarse adjustment of the sensitivity of the device.

External resistor P3 for 100K for fine tuning the sensitivity of the metal detector. We put all resistors in the middle position.

We turn on the power. The device will start beeping.

If there is no squeak, move one coil relative to the other in different directions. The device will beep in two positions, low overlap and medium overlap. But we are only interested in a small overlap, it is at this point that the device detects metal. Position the coils so that a crackling sound is heard in the speaker.

Next, use a variable resistor P1 to achieve the most stable crackle. This is the moment of breakdown of the generator and the maximum sensitivity of the device.

If the metal detector is constantly beeping or silent and does not react in any way to the movement of the coils, the rotation of the P1 resistor, then adjust the device with the P2 resistor.

Resistor P3 is designed to adjust the metal detector after turning on the power, as well as in the event of a battery discharge, it must be slightly adjusted to achieve stable crackling and, accordingly, maximum sensitivity of the device.

To test the operation of the metal detector, bring a metal object to the junction of the two coils, a loud squeak will be heard in the speaker.

It remains to securely fix the coils with hot glue and re-make the final adjustment of the metal detector with resistor P1.

I put all the components in a suitable plastic box, which I bought from a nearby electrical store. I glued the board and the speaker with hot melt glue, inserted eight batteries into a special compartment for batteries.

I brought the handle of the resistor P3 out. The switch was simply stuck into the drilled hole.

To test the device, I went out of town. The weather is just a fairy tale! Metal whispers, find me! There used to be a tractor brigade here …

Here we go! It is a little inconvenient to hold the camera with one hand, hold the metal detector with the other and wade through the dry grass.

Yeah, it seems that he found something!

This is my first find, a large rusty nut. Let’s go looking further …

After half an hour of intensive searches, I collected a small pile of metal.

Wish you luck! See you in new articles!