This article describes the manufacture of the Zabava-m1 metal detector with your own hands. The main difference from Zabava is the location of the working generator next to the coil in the sensor, made of epoxy resin. This location allowed the connecting cable to be removed from the generator and thereby increase the stability of its operation, and therefore increase the actual depth of detection of metal objects.

Technical characteristics of the metal detector Zabava-m1

• supply voltage – 9-12 V;
• current consumption – 17-20 mA;
• selectivity – distinguishes small iron objects from non-ferrous metal objects and iron objects with a large surface area;
• sensitivity adjustment – ​​yes;
• operating principle – “frequency meter”;
• operating mode – dynamic (reacts to metal only when the sensor moves).

Detection distance (in air):

• coin with a diameter of 25 mm – 17 cm;
• canning lid – 31 cm;
• tank lid (diameter 40 cm) – 70 cm;
• maximum detection distance – 100 cm.

The principle of operation of a metal detector

The program written into the microcontroller periodically measures the frequency of the working generator. Analyzing the results of the measurements, the program detects an increase or decrease in the frequency of the working generator and sends a corresponding signal to the headphones.

Fuse bits

CKSEL0, SUT0, SPIEN must be programmed. The rest are not programmed.

Firmware

zabava_Firmware– download program for microcontroller.

How to write a program to a microcontroller

Schematic diagram of the metal detector Zabava-m1

•  https://sdelai-sam.su/spravka_K561LE5.html – brief description of the K561LE5 microcircuit.
•  https://sdelai-sam.su/spravka_CD4001A.html – brief description of the CD4001A microcircuit.
•  https://sdelai-sam.su/spravka_78L05.html – brief description of the 78L05 microcircuit.
•  https://sdelai-sam.su/spravka_attiny2313.html – brief description of the ATtiny2313A microcontroller.
•  https://www.sdelai-sam.su/kd521.html – brief description of the diode KD521.
•  https://sdelai-sam.su/rezistor.html – resistors, resistor marking, resistor connection, etc.
•  https://sdelai-sam.su/kondensator.html – capacitors, capacitor marking, capacitor connection, etc.

Parts list

Microcircuits:

• IC1 – K561LE5 (CD4001A);
• IC2 – ATTINY2313A;
• IC3 – 78L05;
• IC4 – 78L05.

Diodes:

• D1 – KD521.

Resistors:

• R1 – 4.7k;
• R2 – 560 ohm;
• R3 – 1k;
• R4 – 1k;
• R5 – 470оМ;
• R6 – 1k trimmer;
• R8 – RS09-R-30 10k variable.

Capacitors:

• C1, C2 – 4700 pF;
• C3 – 3300 pF;
• C4, C5 – 27 pF;
• C6 – 47uF 16V electrolytic;
• C8 – 47uF 16V electrolytic;
• C7, C9, C10, C13 – 0.1 µF;
• C11 – 47uF 16V electrolytic;
• C12 – 47uF 16V electrolytic.

Coil L1:

• oval coil – 24 by 16 centimeters;
• number of turns – 50;
• wire diameter – 0.3-0.5 mm.

Other details:

• 20-pin socket for microcontroller;
• quartz resonator ZQ – 20 MHz;
• “RESET” button S1 – any button without fixation;
• power switch S2 – MTS-1;
• low-impedance headphones for a player;
• the headphone jack is external and is soldered to a wire about thirty centimeters long;
• connector for a “crown” type battery;
• battery or accumulator of the “crown” type, 9 volts;
• cable entry PG7.

The wire connecting the main board and the generator board is two-wire, each wire in the screen, about 1 meter long.
A single-sided breadboard was used to mount the parts.
The case for the main board is BOX-G01B.
Capacitors C1, C2, C3 should have the lowest possible temperature coefficient (TKE).

How does the homemade metal detector Zabava-m1 work?

The Zabava-m1 metal detector is an “entry-level” metal detector, it is difficult to search with it on highly mineralized soils and littered areas, but it still surpasses beat metal detectors in all parameters . The homemade Zabava-m1 metal detector operates in dynamic mode, which means that the sensor must move relative to the metal object.

When and what signals does the homemade metal detector Zabava-m1 give

Strictly speaking, the metal detector does not react to metal, but to a change in the frequency of the search generator. The metal detector gives two types of signals, one signal is similar to a squeak, let’s call it high-frequency, the second is similar to a crackle, let’s call it low-frequency.

When the sensor approaches a non-ferrous metal object, the generator frequency increases and the program produces a high-frequency signal, then the sensor passes over the object and begins to move away from it, at this moment the generator frequency begins to decrease and the program produces a low-frequency signal. As a result, when the sensor passes over a non-ferrous metal target, we will hear two short signals, the first is high-frequency, the second is low-frequency.

When the sensor passes over a ferrous metal target, the opposite happens. When the sensor approaches the ferrous metal, the generator frequency decreases and a low-frequency signal sounds, when the sensor begins to move away from the ferrous metal object, the generator frequency increases and a high-frequency signal is emitted. As a result, when the sensor passes over a ferrous metal target, we will hear two short signals, the first is low-frequency, the second is high-frequency.

It’s not all that complicated, but there is a fly in the ointment, the fact is that metal detectors react to soil and different minerals, not always of course, there are soils that metal detectors practically “don’t notice” and there are those on which it is impossible to work normally even with very expensive branded metal detectors.

The homemade metal detector Zabava-m1 reacts to the ground in the same way as to a small ferrous metal object, that is, when the sensor approaches the ground, a low-frequency signal sounds, when moving away from the ground, a high-frequency signal sounds. To get rid of ground signals, you have to reduce the sensitivity. You also need to learn how to keep the distance from the sensor to the ground the same when searching, then the ground will not change the generator frequency and false signals will not appear.

How to work with a homemade metal detector Zabava-m1

Before starting work, you need to tune in to the ground in the search area. Set the resistor R8 to maximum sensitivity (rotate clockwise until it stops). Bring the search coil to the ground at a distance of 1 – 2 cm (there should be no metal objects nearby) and, slightly shaking it in the vertical plane, slowly decrease the sensitivity (rotate the regulator counterclockwise), until the signals from the ground in the headphones disappear.

When searching, the coil should be moved above the ground at a speed of approximately 0.5 m/sec, trying to maintain the distance from the ground to the coil the same all the time. In most cases, when a metal object is detected, the metal detector gives a double signal.

If the first signal was high frequency and the second was low frequency, then the object found is non-ferrous metal or iron with a large surface area. If the first signal is low frequency and the second is high frequency, then the find is a small iron object.

To determine the exact location of a non-ferrous metal object, you need to raise the coil above the ground, then lower it vertically to the ground at the supposed location of the object. If a low-frequency signal sounds when lowering, then there is no non-ferrous metal under the coil. If the coil is lowered exactly above the non-ferrous metal, then a high-frequency signal will sound (provided that the soil is not heavily mineralized). In the same way, you can examine pits, as well as areas heavily littered with small iron objects, rust, coals, etc.

At maximum sensitivity, the metal detector may constantly give false signals. This happens due to unstable operation of the search generator, the reason may be in C1 and C2, in the coil or in the fragile design of the rod and sensor. If false signals occur at sensitivity levels at which the metal detector previously worked normally, this means the battery is discharged.

Be careful when connecting the battery – it is unacceptable to confuse the plus with the minus, even briefly. If you “reverse the plus”, the metal detector may fail.