MD receiver circuit - second option
Metal detector parameters
Operating frequency - about 2 kHz;
- detection depth of a coin with a diameter of 25 mm - 9 cm;
- iron sealing lid from a jar - 25 cm;
- aluminum sheet measuring 200x300 mm - 45 cm;
- sewer hatch - 60 cm.
The search coils connected to it must be exactly the same in size and winding data. They must be positioned so that in the absence of foreign metal objects there is practically no connection between them; examples of coils are shown in the figure.
If the transmitter and receiver coils are positioned this way, the transmitter signal will not be heard in the receiver. When a metal object appears in the vicinity of this balanced system, under the influence of the alternating magnetic field of the transmitting coil, so-called eddy currents arise in it and, as a result, its own magnetic field, which induces an alternating EMF in the receiving coil.
The signal received by the receiver is converted by phones into sound. The metal detector circuit is really very simple, but despite this, it works quite well, and the sensitivity is not bad. The multivibrator of the transmitting unit can be assembled using other transistors of a similar structure.
The metal detector coils have a size of 200x100 mm and contain about 80 turns of 0.6-0.8 mm wire. To check the operation of the transmitter, connect headphones instead of the L1 coil and make sure that sound is heard in them when the power is turned on. Then, by connecting the coil in place, they control the current consumed by the transmitter - 5...8 mA.
The receiver is configured with the input closed. By selecting resistor R1 in the first stage and R3 in the second, a voltage equal to approximately half the supply voltage is set on the collectors of the transistors, respectively. Then, by selecting resistor R5, they ensure that the collector current of transistor VT3 becomes equal to 5...8 mA. After this, opening the input, connect the receiver coil L1 to it and, receiving the transmitter signal at a distance of about 1 m, make sure that the device is working.
Simple transistor metal detector
Purpose: Detection of objects made of steel and iron.
Schematic diagram.
The diagram of a simple transistor metal detector is shown in Fig.1. It consists of a high-frequency generator and a receiver, which registers changes in the frequency of the generator when metal objects approach it.
Schematic diagram of a metal detector. Fig.1
Receiver heterodyne type metal detector. It is made on just one transistor V2, and combines the functions of a local oscillator and a detector.
Heterodyne assembled according to a three-point capacitive circuit. The advantage of this scheme is the use of an inductor without taps, which is very convenient for beginner radio amateurs.
The oscillatory circuit contains an inductor L2 and a capacitance made up of series-connected capacitors C4-C6. The local oscillator frequency can be changed by tuning the L2 coil.
High frequency generator assembled on transistor VI also according to a three-point capacitive circuit. The frequency of the generator depends on the inductance of the coil L1, which is made in the form of a frame. If there is a metal object near the coil, its inductance will change. This will lead to a change in the frequency of the generator, which will be immediately registered by the receiver. If, for example, the generator is initially tuned to a frequency of 465 kHz, and the receiver local oscillator is tuned to a frequency of 465.5 kHz, then a signal with a frequency of 500 Hz will be heard in phones. When the L1 coil approaches the metal, the tone of the signal in the phones will change. This will serve as a signal for detecting a metal object.
Element base
In addition to the transistors indicated in the diagram, you can use germanium transistors of the P401, P402 series.
Telephones - TON-1 or TON-2. Moreover, both capsules must be connected in parallel so that the total resistance of the phones is 800-1200 Ohms.
All resistors can be MLT-0.125 or MLT-0.25, capacitors - KLS-1 or BM-2, power switch - single-pole toggle switch.
Reels
Coil L1 is a rectangular frame with dimensions 175 x 230 mm made of 32 turns of PEV-2 0.35 wire.
The design of coil L2 is shown in Rice. 2. Two cylindrical frames contain sections of a rod with a diameter of 7 mm made of 400NN or 600NN ferrite:
*the first frame is 20-22 mm long
*second frame 35-40 mm long, for adjusting the coil. The frames are wrapped with paper tape, on top of which a coil is wound - 55 turns of PELSHO 0.2 wire (PEV-1 or PEV-2 can be used), the coil terminals are secured with glue. (Frames from IF circuits of old tube TVs and radios are applicable.)
Printed circuit board
A drawing of the printed circuit board is shown on Rice. 3. The board must be connected to the coils, battery, switch and connector XI using a flexible stranded wire in insulation.
Printed circuit board of a transistor metal detector. Fig.3
Coil location.
Structurally, coil L2 must be installed at a distance of 5-7 mm from the turns of coil L1.
Setting up a metal detector.
After applying the supply voltage, we check the modes indicated in the diagram, and then slowly move the tuning core of the L2 coil to achieve a loud, pure low-frequency tone in the phones. Then, bringing a metal object closer to the frame, we record the beginning of a change in the tone of the sound. As a rule, this occurs at a distance of 30-40 cm from the object. Next, by more accurately adjusting the local oscillator frequency, achieve the highest sensitivity of the metal detector.
Download the metal detector printed circuit board from the server in the format lay6 You do not have access to download files from our server
Despite its extreme simplicity, the circuit works well and provides performance no worse than more complex circuits (detects a large coin at a distance of 10 cm). The circuit uses elementary, non-scarce parts; it can be assembled using parts from an old radio.
However, assembly and adjustment have their own characteristics that must be taken into account, and when using this metal detector there is an inconvenience in adjusting the operating frequency of the generator (it is not very convenient to select the position of the trimming rod by fractions of a millimeter in a forest or field), in addition, the published diagram has the following disadvantage: like using high impedance headphones, which are hard to find these days. On ordinary headphones for audio equipment, the sound is practically inaudible. I offer a description of the circuit, modified to take into account these shortcomings, and a simple method for manufacturing the metal detector itself.
The circuit is supplemented with an amplifier (it is highlighted with a dotted line), assembled on a composite transistor (T3 + T4). This allows you to use conventional headphones with an impedance of 30...60 Ohms and at the same time ensure an economical operating mode. Transistors P416B can be replaced with P416, P401, P402, P422 (these were used in old transistor radios), KT503 with KT315 or KT342, and KT502 with KT603, KT608, KT626. Printed circuit boards and the location of the transistor pins are shown in Fig. 2. The first board contains generators; the board is small in size and placed in a small plastic box, which is then glued to the coil-frame L1 (its design will be discussed later). The second board contains an additional amplifier with a headphone jack and contact pads for three AA batteries. Pads (petals) can be cut out of tin from a tin can, given the desired shape and soldered to the contact pads of the printed circuit board. In addition, this board contains a variable resistor with a resistance of 100 ... 150 Ohms, which can be used to change the supply current of generators within small limits and thus carry out precise frequency adjustment, which is very convenient in “field” conditions. This board is also placed in a small box (a metal one is also possible here) and mounted on the metal detector rod next to the handle. The boards will be connected using a regular unshielded three-core cable and the appropriate suitable connectors (can be SG-3, SG-5 or any others). In the circuit shown here, the headphone jack also serves as the power switch (shown in Fig. 2.). For this, a mono plug is used, the “long” contact of which closes the power circuit of the circuit. But you can, of course, install a simple switch if the dimensions of the case allow it. Then the “minus” power from the batteries must be supplied through this switch to the “minus” connector of the cable and the headphone jack.
This development board was made for general setup of the circuit, but you can also use it as a working board by placing it in an appropriate case. But I want to offer an option for making a frame that is simpler and more aesthetic, and also does not require a case. To do this, you need a piece of plastic cable duct (box), which is used for laying electrical wiring. It is sold in any electrical goods stores. The minimum cross-sectional size is required - 7 x 12, 10 x 15 mm. The cover is removed from the cable channel and cuts are made into the walls with a sharp thin knife at distances equal to the sides of the frame (175 x 230 mm). Then the channel is bent at the places of these cuts and its ends are glued together. All this is shown in the figure below:
32 turns of PEV (PEL) wire 0.3...0.35 are wound onto the resulting rectangular frame. Then the frame is closed with a lid. You can fill the coils in the channel with epoxy, this will give the frame greater rigidity. This will be coil L1. Coil L2 contains two pieces of ferrite rod with a diameter of 8 mm - one 20 ... 25 mm long, the second 35 ... 40 mm. The rod can also be taken from an old radio receiver (it is used there as an antenna for the MF and LW bands). The necessary pieces of the rod can be broken off by clamping it in a vice to the required length (clamp it carefully, through cardboard or rubber spacers, as it is very fragile!). Ferrite pieces are inserted into cardboard “sleeves”; you can use a felt-tip pen body of a suitable diameter. Both “sleeves” are glued together and wrapped with several layers of paper tape, also impregnated with glue, to give the structure rigidity. Then, turn to turn, 55 turns of PELSHO 0.2 wire are wound on top (I tried PEL 0.2...0.3, no worse) and fixed with glue or electrical tape. The coil design is shown in Fig. 3. A short piece of ferrite is permanently fixed, while a long piece remains movable to adjust the frequency of the generator. Next, the printed circuit board with generators and coil L2 is placed in a suitable plastic case (not metal!) and glued to one of the short sides of the coil-frame from the inside so that the distance between coils L1 and L2 is no more than 5 ... 8 mm. Electromagnetic coupling must be ensured between the coils. Power to the generators and audio signal output are provided through a connector and a piece of connecting cable about 1 m long.
The batteries and amplifier are located in a separate housing near the handle of the device. The design is shown in the photo. The dimensions of the case depend mainly on the type of batteries used (any round - large or small). You can use one headphone, since you are unlikely to achieve a special stereo effect J. But it is still better to use two, and turn them on in parallel. In this way, you can further increase the sound volume, although the current consumption from the batteries will increase slightly. In general, with normal headphones of average quality, the volume is quite sufficient.
Setting up
First, the operating modes of transistors T1 and T2 are checked. At the T1 base there should be -2.1 V, at the T2 base -1V (relative to the positive wire of the circuit). If necessary, these voltages can be adjusted by selecting resistors R2 and R4, respectively. A deviation of 10-15% from the specified voltages is allowed. Then we put the R10 engine in the middle position and, by moving the movable core L2, we achieve the appearance of low-frequency sound in the headphones. The lower the sound frequency, the more sensitive the device will be. In this position we fix the core with glue or paraffin. In the future, the frequency of the generator can be adjusted within small limits using resistor R10. The rod (handle) of the device must be wooden or plastic...
You can download printed circuit boards in LAY format below
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad |
|---|---|---|---|---|---|---|
| T1, T2 | Bipolar transistor | P416B | 2 | P416, P401, P402, P422 | To notepad | |
| T3 | Bipolar transistor | KT503E | 1 | KT315, KT342 | To notepad | |
| T4 | Bipolar transistor | KT502E | 1 | KT603, KT608, KT626 | To notepad | |
| C1, C5 | Capacitor | 1000 pF | 2 | To notepad | ||
| C2, C6 | Capacitor | 3300 pF | 2 | To notepad | ||
| C3 | Capacitor | 300 pF | 1 | To notepad | ||
| C4 | Capacitor | 100 pF | 1 | To notepad | ||
| C7, C8 | Capacitor | 0.01 µF | 2 | To notepad | ||
| C9 | Capacitor | 0.33 µF | 1 | To notepad | ||
| R1, R6, R7 | Resistor | 1 kOhm | 3 | To notepad | ||
| R2, R3, R5 | Resistor | 4.7 kOhm | 3 | To notepad | ||
| R4 | Resistor |
With the onset of spring, more and more often you can see people with metal detectors on the banks of rivers. Most of them are engaged in “gold mining” purely out of curiosity and passion. But a certain percentage actually earn a lot of money from searching for rare things. The secret to the success of such research is not only in experience, information and intuition, but also in the quality of the equipment with which they are equipped. A professional instrument is expensive, and if you have a basic knowledge of radio mechanics, you have probably thought more than once about how to make a metal detector with your own hands. The editors of the site will come to your aid and tell you today how to assemble the device yourself using diagrams.
Read in the article:
This model costs more than 32,000 rubles, and, of course, non-professionals will not be able to afford such a device. Therefore, we suggest studying the design of a metal detector in order to assemble a variation of such a device yourself. So, the simplest metal detector consists of the following elements.
The operating principle of such metal detectors is based on the transmission and reception of electromagnetic waves. The main elements of a device of this type are two coils: one is transmitting, and the second is receiving.
The metal detector works like this: the magnetic field lines of the primary field (A) of red color pass through the metal object (B) and create a secondary field (green lines) in it. This secondary field is picked up by the receiver and the detector sends an audible signal to the operator. Based on the principle of operation of emitters, electronic devices of this type can be divided into:
The cheapest devices belong to the first type.
An induction metal detector has one coil that sends and receives a signal simultaneously. But devices with pulse induction differ in that they generate a transmitter current, which turns on for a while and then turns off abruptly. The coil field generates pulsed eddy currents in the object, which are detected by analyzing the attenuation of the pulse induced in the receiver coil. This cycle repeats continuously, perhaps hundreds of thousands of times per second.
The operating principle of a metal detector varies depending on the type of device. Let's consider the main ones:
Depth detectors operate on two coils, one is parallel to the ground surface, the other is perpendicular.
The simplest devices that you can assemble yourself include devices that operate on the principle of reception and transmission. There are schemes that even a novice radio amateur can do; for this you just need to select a certain set of parts.
There are many video instructions on the Internet with detailed explanations of how to make a simple metal detector with your own hands. Here are the most popular ones:
However, despite the fact that some entertainers are trying to offer systems for assembling a metal detector from a phone, such designs will not pass the battle test. It’s easier to buy a children’s metal detector toy, it will be more useful.
And now more about how to make a simple metal detector with your own hands using the example of the “Pirate” design.
Homemade products based on the “Pirate” series metal detector are among the most popular among radio amateurs. Thanks to the good performance of the device, it can “detect” an object at a depth of 200 mm (for small items) and 1500 mm (large items).
The Pirate metal detector is a pulse type device. To make the device you will need to purchase:
The classic circuit of the “Pirate” series metal detector is built using the NE555 microcircuit. The operation of the device depends on a comparator, one output of which is connected to the IC pulse generator, the second to the coil, and the output to the speaker. If metal objects are detected, the signal from the coil is sent to the comparator, and then to the speaker, which notifies the operator of the presence of the desired objects.
The board can be placed in a simple junction box, which can be purchased at an electrical store. If such a tool is not enough for you, you can try to make a more advanced device; a diagram for making a gold-oriented metal detector will help you.
This device uses Soviet-style transistors KT-361 and KT-315 to generate signals (you can use similar radio components).
The pulse generator is assembled on the NE555 chip. By selecting C1 and 2 and R2 and 3, the frequency is adjusted. The pulses obtained as a result of scanning are transmitted to transistor T1, and it transmits the signal to transistor T2. The audio frequency is amplified using the BC547 transistor to the collector, and headphones are connected.
To place radio components, a printed circuit is used, which can be easily made independently. To do this, we use a piece of sheet getinax covered with copper electrical foil. We transfer the connecting parts onto it, mark the fastening points, and drill holes. We cover the tracks with a protective varnish, and after drying, we lower the future board into ferric chloride for etching. This is necessary to remove unprotected areas of copper foil.
For the base you will need a ring with a diameter of about 200 mm (ordinary wooden hoops can be used as the base), on which 0.5 mm wire is wound. To increase the depth of metal detection, the coil frame should be in the range of 260−270 mm, and the number of turns should be 21−22 vol. If you don't have anything suitable on hand, you can wind a reel on a wooden base.
| Illustration | Description of action |
 | For winding, prepare a board with guides. The distance between them is equal to the diameter of the base on which you will attach the reel. |
 | Wind the wire around the perimeter of the fastenings in 20-30 turns. Secure the winding with electrical tape in several places. |
 | Remove the winding from the base and give it a rounded shape; if necessary, additionally fasten the winding in several more places. |
 | Connect the circuit to the device and test its operation. |
We will need: 1 twisted pair 5 cat 24 AVG (2.5 mm), knife, soldering iron, solder and multitester.
| Illustration | Description of action |
 | Twist the wire into two skeins. Leave 10 cm on each side. |
 | Strip the winding and free the wires for connection. |
 | We connect the wires according to the diagram. |
 | For better fastening, solder them with a soldering iron. |
 | Test the coil in the same manner as the copper wire device. The winding terminals must be soldered to a stranded wire with a diameter in the range of 0.5-0.7 mm. |
Once the main elements of the metal detector are ready, we proceed to assembly. We attach all the components to the metal detector rod: the body with the coil, the receiving and transmitting unit and the handle. If you did everything correctly, then additional manipulations with the device will not be required, since it initially has maximum sensitivity. Fine tuning is performed using variable resistor R13. Normal operation of the detector should be ensured with the regulator in the middle position. If you have an oscilloscope, then use it to measure the frequency at the gate of transistor T2, which should be 120−150 Hz, and the pulse duration should be 130−150 μs.
The principle of assembling an underwater metal detector is no different from a conventional one, with the only difference being that you will have to work hard to create an impenetrable shell using sealant, as well as to place special light indicators that can report a find from under water. An example of how this will work is in the video:
The Terminator 3 metal detector has occupied an honorable place among homemade metal detectors for many years. The two-tone device operates on the principle of induction balance.
Its main features are: low power consumption, metal discrimination, non-ferrous metals mode, gold only mode and very good search depth characteristics, compared to semi-professional branded metal detectors. We offer you the most detailed description of the assembly of such a device from folk craftsman Viktor Goncharov.
Metal discrimination is the ability of the device to distinguish between the detected material and classify it. Discrimination is based on different electrical conductivities of metals. The simplest methods for determining the types of metals were implemented in old instruments and entry-level devices and had two modes - “all metals” and “non-ferrous”. The discrimination function allows the operator to respond to a phase shift of a certain magnitude, compared to a configured (reference) level. In this case, the device cannot distinguish between non-ferrous metals.
Learn how to make a homemade professional metal detector using improvised materials in this video:
Metal detectors of this type can detect objects at great depths. A good metal detector, made by yourself, looks to a depth of 6 meters. However, in this case the size of the find must be substantial. These detectors work best for detecting old shells or large enough debris.
There are two types of deep metal detectors: frame and transceiver on a rod. The first type of device is capable of covering a large area of land for scanning, however, in this case, the efficiency and focus of the search is reduced. The second version of the detector is a point detector; it works directed inward over a small diameter. You need to work with it slowly and carefully. If your goal is to build such a metal detector, the following video can tell you how to do it.
If you have experience in assembling such a device and using it, tell others about it!
This metal detector is capable of detecting: large metal objects (iron bucket, manhole cover, water pipe) at a depth of up to one meter, as well as small objects (coins or screws) at a depth of 15-20 cm.
The device is built on the basis of the most common parts that are available in the supplies of any radio amateur. The metal detector is made according to the well-known and widely used principle in such devices of beats between the frequencies of two high-frequency generators. The frequency of one of them (reference) is constant, and the frequency of the second (search) changes under the influence of external metal objects that change the inductance of its coil when it enters its action zone.
The schematic diagram of the metal detector is shown in Fig. 1. The reference oscillator is made on transistor VT1. Its oscillation frequency is determined by the parameters of the L1C3 circuit and is about 1 MHz.
The search generator is made on transistor VT2; it also produces a signal of approximately the same frequency. The difference is that the reference oscillator circuit uses a small coil with a ferrite core.
Fig 1. Schematic diagram of a simple homemade metal detector.
Therefore, external metal objects have practically no significant effect on its inductance.
The coil of the search generator circuit is wound on a larger frame in the form of a frame. It has no core. As a result, its inductance changes greatly as it approaches a metal object, which in this case begins to act as a moving core.
Signals from both generators are sent to a diode mixer using diode VD1. As a result, the product of subtraction of generator frequencies is obtained on capacitor C12.
The closer the values of these frequencies, the lower the audio tone on this capacitor, and the more different the frequencies of the generators are, the higher the sound tone in speaker B1, to which the signal is received (the product of the diode mixer).
The signal enters through a low-frequency amplifier using transistors VTZ-VT6.
Using a variable capacitor C7, the search generator can be configured in such a way that, in the absence of metal objects nearby, the sound tone in the speaker is the lowest.
Then, as coil L2 approaches the metal, the frequency of the generator at VT2 begins to change. The frequency difference between the generators increases, and therefore the tone in the dynamics will rise. When the metal is precisely located, the sound will turn into a piercing squeak.
Coil L1 should be wound on a ferrite rod with a diameter of 8 mm, for example, from a magnetic antenna of a radio receiver. The length of the rod is reduced to 30 mm.
First, you need to put a frame on the rod - a sleeve glued together from whatman paper, which moves along it with some friction.
Coil L1 should contain 110 turns of PEV wire with a diameter of 0.2-0.3 mm. The tap must be made from the 16th turn counting from the VT1 collector.
Coil L2 is a search coil. It must be wound on a frame, which is a frame measuring 120 x 220 mm, made of plexiglass, plastic or wood.
Winding should be done with PEV wire with a diameter of 0.4 x 0.6 mm. The coil should contain 45 turns with a tap from the 10th, counting from the VT2 collector.
The coil must be connected to the main unit with a three-core shielded wire. The coil should be located at a distance of about 1 meter from the main unit (attached to an aluminum tube or wooden strip).
The device itself (the main unit containing a generator on VT1 and an ultrasonic sounder with a speaker and a battery) can be mounted in a housing from a radio receiver. From the same receiver it is advisable to use:
The design may be different, it all depends on capabilities and desires.
Capacitor C7 can have a minimum capacitance of no more than 10 pF, and a maximum of no less than 150 pF.
Transistors KT315 can be replaced with KT3102 or KT312, KT316. Transistors MP35 can be replaced with MP35-MP38, and transistor MP39 with MP39-MP42.
Diodes D9 - with any letter, or D2, D18, GD507. Speaker - any resistance from 4 ohms to 100 ohms, for example, a speaker from a radio receiver or headphones. The battery is 9 V, you can use a “Krona” or a suitable battery.
Attention:Power supply from a 220 V mains source is not advisable, because this creates an alternating current background and reduces the sensitivity of the device as a whole.
The setting consists of adjusting coil L1 in such a way that when the rotor of capacitor C7 is in the middle position and in the absence of external metal objects, the sound of the lowest tone is heard in the speaker.
In the future, during operation, adjustment before starting the search will be made by capacitor C7.
If there are no oscillations from the generator at VT1, you need to select the value of C4 and/or adjust the operating mode of the cascade by selecting the value of R2. If the generator at VT2 is not excited, you need to adjust C8 and adjust the operating 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 is important to take into account that when approaching ferrous metals (iron, steel, cast iron), the frequency of the generator on VT2 decreases, and when approaching non-ferrous metals, it increases.
