Metal detector from the available elements. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Metal detector from the available elements. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / metal detectors

Comments on the article

This metal detector is able to detect such large metal objects as an iron bucket or a manhole cover, a water pipe, at a depth of up to one meter, and it can detect such small objects as coins or screws at a depth of up to 15-20 cm.

The device is built on the basis of the most common parts that are available in the stocks of any radio amateur. The metal detector is made according to the well-known and widely used in such devices principle of beating between the frequencies of two high-frequency generators, the frequency of one of which is constant, and the frequency of the second one changes under the influence of external metal objects that change the inductance of its coil when it hits its perimeter zone.

The circuit diagram is shown in the figure.

Metal detector from available elements

The constant frequency generator is made on the transistor VT1. The frequency of its oscillations is determined by the parameters of the L1C3 circuit and is about 1 MHz. The second generator is made on the transistor VT2, it also generates a signal of approximately the same frequency. The difference is that in the first generator, in its circuit, a small coil with a ferrite core is used, and external metal objects practically do not have a significant effect on its inductance. The coil of the circuit of the second generator, on the contrary, is wound on a large frame in the form of a frame and it does not have a core. As a result, its inductance changes greatly when it approaches a metal device, which in this case begins to perform the functions of a moving core.

The signals from both generators are fed to the diode mixer on the diode VD1 and on the capacitor C12 the product of subtracting the frequencies of the generators is obtained. The closer these frequencies are, the lower the frequency of the AF on this capacitor, and the more the frequencies of the generators differ, the higher the tone of the sound in speaker B1, to which the signal - the product of the operation of the diode mixer, enters through a low-frequency amplifier on transistors VT3-VT6.

Thus, using a variable capacitor C7, the second generator is tuned in such a way that, in the absence of metal objects nearby, the sound tone in the speaker is the lowest. Then, when the coil L2 approaches the metal, the frequency of the generator on VT2 begins to change and the difference in the frequencies of the generators increases, and therefore the tone in the dynamics will rise, and when the metal is exactly located, it will turn into a shrill squeak.

Coil L1 is wound on a ferrite rod with a diameter of 8 mm from the magnetic antenna of the radio. The length of the rod was reduced to 30 mm (the rod was filed with a file for medical ampoules and broken off). Previously, a frame is put on the rod - a sleeve glued from whatman paper, which moves along it with some friction. The coil contains 110 turns of PEV wire with a diameter of 0,2-0,3 mm. The tap is made from the 16th turn, counting from the VT1 collector.

The L2 coil is a search coil, it is wound on a frame, which is a 120X220 mm frame made of plexiglass, plastic or wood. Winding is carried out with a PEV wire with a diameter of 0,4-0,6 mm, the coil contains 45 turns with a tap from the 10th counting from the VT2 collector. The coil is connected to the main unit with a three-core shielded wire (you can use a low-frequency audio cord). The coil is located at a distance of about 1 meter from the main unit (fixed on an aluminum tube or wooden rail).

The device itself (the main unit containing a generator on VT1 and an ultrasonic frequency converter with a speaker and a battery) is mounted in a case from a faulty radio receiver, a speaker and a variable capacitor, and a rod for the L1 coil are used from the same receiver. Installation is carried out on a completely dismantled board of this receiver using where possible the tracks, or mounting wires. The design may be different, it all depends on the possibilities and desires. Capacitor C7 can be with a minimum capacitance of not more than 10 pF, and a maximum capacitance of at least 150 pF. Transistors KT315 can be replaced with KT3102 or KT312, KT316. MP35 transistors can be replaced with MP35-MP38. and the MP39 transistor on MP39-MP42. Diodes D9 with any letter, or D2, D18, GD507. Any speaker with resistance from 4 to 100 ohms, for example, a speaker from a radio receiver or headphones.

A 9V power battery, in this case two 4,5V "flat batteries" connected in series, but you can use a 9V "Krona" or a battery of six 1,5V cells. Power supply from a mains source is not desirable, in this case an alternating current background appears and the sensitivity of the device as a whole decreases.

The setting consists in adjusting L1 so that when the rotor of the capacitor C7 is in the middle position, in the absence of external metal objects in the speaker, the sound of the lowest tone is heard. In the future, during operation, adjustment before the start of the search will be performed by capacitor C7.

In the absence of generator generation on VT1, you need to select the value of C4 or (and) adjust the operation mode of the cascade by selecting the value of R2. If the generator on VT2 is not excited, you need to adjust C8 and adjust the operation mode of the transistor by selecting the value of R6.

The device is highly sensitive and working with it requires certain skills, so you need to practice.

When working, it must be borne in mind that approaching ferrous metals (iron, steel, cast iron), the frequency of the generator on VT2 decreases, and when approaching non-ferrous metals, it increases.

Author: S.Pavlov

See other articles Section metal detectors.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive

Offshore hydrogen production 05.06.2022

Germany plans to invest in research into the possibility of producing hydrogen on the high seas.

It is planned to invest 2 billion euros in the research of hydrogen technologies in the production of electricity at offshore wind farms over four years.

To implement its plan, Germany is going to strengthen cooperation with Australia.

"The idea is that in just a few years ships would be transporting green hydrogen from solar and wind energy from Australia to Germany," said German Education and Research Minister Bettina Stark-Watzinger.

According to the Ministry of Industry, Science and Technology of this country, the total amount of government investment in the development of the hydrogen industry over the past three years has exceeded 1,5 billion Australian dollars ($1,1 billion).

Other interesting news:

▪ Dense bulletproof tree

▪ Rugged smartphone Blackview BV8900 with a thermal imager

▪ Two new inductors from Vishay

▪ Extreme Camera Olympus TG-Tracker

▪ Solar panels are thinner than cobwebs

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ Modeling section of the site. Selection of articles

▪ article Measures to improve the sustainability of the functioning of the object of the economy in an emergency. Basics of safe life

▪ article Why do our milk teeth fall out? Detailed answer

▪ article Falcata Japanese. Legends, cultivation, methods of application

▪ article Indicator of radio emission in the range of 27 MHz. Encyclopedia of radio electronics and electrical engineering

▪ article Regulated voltage power supply, 220/0-20 volts, 0,4 amps. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages of this page

Home page | Library | Articles | Website map | Site Reviews