The metal detector circuit has a very high sensitivity, since the frequency discrepancy is controlled here - an exemplary generator operating at a frequency of 0.5 ... 1 MHz, and 5 ... 10 harmonics of the search generator. The detuning of the latter, for example, only by 10 Hz leads to a change in the frequency of difference oscillations by 50 ... 100 Hz. The metal detector “catches” a 2 cm coin at a depth of up to 9 cm.

The exemplary generator of the metal detector is made on the elements DD2.1, DD2.2, ZQ1, etc., where ZQ1 is a quartz resonator with a frequency f0 = 0.5..1 MHz, which ensures its high stability.

The tunable oscillator circuit (L1, C2, NW, VD1) must be tuned to one of the frequencies fc=k f0, where kO(1/10, 1/9, 1/8, 1/7, 1/6, 1/ 5). It is selected by the capacitor C2 (the engine of the resistor R2 - the fine-tuning element of the generator - should be in the middle position).

The mixer of the device is made on the element DD1.4. Elements DD1.3 and DD2.3 are buffer.

The frame of the search coil L1 is a ring with a diameter of 250 mm, bent from a vinyl plastic tube with an outer diameter of 15 and an inner diameter of 10 mm. The coil is wound with PELSHO 0.27 wire. It has 100 turns. For the convenience of winding, the vinyl plastic tube may have a longitudinal section. After laying the turns of the coil, the tube is wrapped with aluminum foil tape, which is needed here as an electrostatic shield. A 1 cm long gap must be made in this screen, otherwise it will become a short-circuited loop bypassing L1. To protect the search coil from mechanical damage, it is wrapped with two or three layers of PVC tape.

The elements of the device are placed on the board, which is placed in a metal box-screen. The extension cord, if any, must also be metal. It can be made, for example, from a duralumin ski pole, and if wooden, then the wire to the coil must be shielded.

Why you need a metal detector does not even need to be said. This is not only, in some cases, a practical thing to find the lost, but also an opportunity to be romantic, in search of lost treasures or just old metal utensils.
In this article, we will provide a description and wiring diagram of a sensitive metal detector. A feature of this metal detector is good sensitivity when searching for metals with weak ferromagnetic properties, such as, for example, copper, tin, silver. A significant effect is the use of quartz.

Wiring diagram of a sensitive metal detector

The metal detector, the schematic diagram of which is shown in fig. 1,a, consists of a measuring oscillator assembled on a transistor VT1, and a buffer stage - an emitter follower assembled on a transistor VT2, separated by a quartz resonator ZQ1 from an indicator device - a detector on a diode VD2 with a DC amplifier on a transistor VT3. The load of the amplifier is a pointer device With a total deflection current of 1 mA. Due to the high quality factor of the quartz resonator, the slightest changes in the frequency of the measuring oscillator will lead to a decrease in the impedance of the latter, as can be seen from the characteristic shown in Fig. 1b, and this will ultimately increase the sensitivity of the device and the accuracy of measurements. Preparation for the search consists in tuning the oscillator to the parallel resonance frequency of quartz equal to 1 MHz. This setting is made by capacitors of variable capacitance C2 (roughly) and trimmer capacitor C1 (finely) in the absence of metal objects near the frame. Since quartz is an element of communication between the measuring and indicating parts of the device, its resistance at the time of resonance is large and the minimum reading of the pointer device indicates the fine tuning of the device.
The sensitivity level is regulated by a variable resistor R8. A feature of the device is the ring frame L1, made from a piece of cable. The central core of the cable is removed and six turns of PEL-type wire 0.1–0.2 mm 115 mm long are pulled instead. The design of the frame is shown in Figure 1, c. This frame has a good electrostatic screen.

Rice. 1. Small-sized sensitive metal detector

The structural rigidity of the metal detector frame is ensured by placing it between two discs made of plexiglass or getinaks with a diameter of 400 mm and a thickness of 5–7 mm. The device uses KT315B transistors, a reference diode - a zener diode 2S156A, a detector diode of the D9 type with any letter index. The quartz frequency can be in the frequency range from 90 kHz to 1.1 MHz. Cable - type RK-50.

Sensitive compact metal detector using a quartz resonator

Metal detectors based on beat registration turn out to be insensitive when searching for metals with weak ferromagnetic properties, such as, for example, copper, tin, silver. It is impossible to increase the sensitivity of metal detectors of this type, since the difference in beat frequencies is hardly noticeable with conventional indication methods. A significant effect is the use of quartz metal detectors. The metal detector, the schematic diagram of which is shown in fig. 1, a, consists of a measuring oscillator assembled on a VT1 transistor and a buffer stage - an emitter follower assembled on a VT2 transistor, separated by a ZQ1 quartz resonator from an indicator device - a detector on a VD2 diode with a DC amplifier on a VT3 transistor. The load of the amplifier is a pointer device with a total deflection current of 1 mA.

Fig.1. (Small size sensitive metal detector)

Due to the high quality factor of the quartz resonator, the slightest changes in the frequency of the measuring oscillator will lead to a decrease in the impedance of the latter, as can be seen from the characteristic shown in Fig. 1b, and this will eventually increase the sensitivity of the device and the accuracy of measurements.

Preparation for the search consists in tuning the oscillator to the parallel resonance frequency of quartz equal to 1 MHz. This setting is made by capacitors of variable capacitance C2 (roughly) and trimmer capacitor C1 (finely) in the absence of metal objects near the frame. Since quartz is an element of communication between the measuring and indicating parts of the device, its resistance at the time of resonance is large and the minimum reading of the pointer device indicates the fine tuning of the device. The sensitivity level is regulated by a variable resistor R8.

A feature of the device is the ring frame L1, made from a piece of cable. The central core of the cable is removed and six turns of PEL-type wire 0.1-0.2 mm 115 mm long are pulled instead. The design of the frame is shown in fig. 1, a. This frame has a good electrostatic screen.

The rigidity of the frame structure is ensured by placing it between two disks made of organiglass or getipak with a diameter of 400 mm and a thickness of 5-7 mm.

The device uses KT315B transistors, a reference diode - a zener diode 2S156A, a Tina D9 detector diode with any letter index. The quartz frequency can be in the frequency range from 90 kHz to 1.1 MHz. Cable - type RK-50.

THE BEST METAL DETECTOR

Why was the Volksturm named the best metal detector? The main thing is that the scheme is really simple and really working. Of the many metal detector circuits that I personally made, this is where everything is simple, deep-cutting and reliable! Moreover, with its simplicity, the metal detector has a good discrimination scheme - the definition of iron or non-ferrous metal is in the ground. Assembling the metal detector consists in error-free soldering of the board and setting the coils to resonance and to zero at the output of the input stage on the LF353. There is nothing super complicated here, it would be a desire and brains. We look constructive execution of the metal detector and a new improved scheme Volksturm with a description.

Since questions arise during the build to save you time and not force you to flip through hundreds of forum pages, here are the answers to the 10 most popular questions. The article is in the process of being written, so some points will be added later.

1. How does this metal detector work and detect targets?
2. How to check if the metal detector board is working?
3. Which resonance should I choose?
4. What are the best capacitors?
5. How to adjust resonance?
6. How to zero coils?
7. Which coil wire is best?
8. What parts can be replaced and with what?
9. What determines the depth of the search for goals?
10. Power supply for the Volksturm metal detector?

The principle of operation of the Volksturm metal detector

I will try in a nutshell about the principle of operation: transmission, reception and balance of induction. In the search sensor of the metal detector, 2 coils are installed - transmitting and receiving. The presence of metal changes the inductive coupling between them (including the phase), which affects the received signal, which is then processed by the display unit. Between the first and second microcircuits there is a switch controlled by pulses of a phase-shifted generator relative to the transmitting channel (i.e. when the transmitter is working, the receiver is turned off and vice versa, if the receiver is turned on, the transmitter is resting, and the receiver calmly catches the reflected signal in this pause). So, you turned on the metal detector and it beeps. Great, if it beeps, then many nodes are working. Let's figure out why exactly he squeaks. The generator on y6B constantly generates a tone signal. Then it enters the amplifier on two transistors, but the unch will not open (do not miss the tone) until the voltage at the output of u2B (7th pin) allows it to do so. This voltage is set by changing the mode using this same trash resistor. They need to set such a voltage so that the Unch almost opens and misses the signal from the generator. And the input couple of millivolts from the metal detector coil, having passed the amplifying cascades, will exceed this threshold and it will open completely and the speaker will squeak. Now let's trace the passage of the signal, or rather the response signal. On the first stage (1-y1a) there will be a couple of millivolts, up to 50 is possible. On the second stage (7-y1B) this deviation will increase, on the third one (1-y2A) there will already be a couple of volts. But without a response everywhere at the outputs by zeros.

How to check if the metal detector board is working

In general, the amplifier and key (CD 4066) are checked with a finger at the RX input contact at maximum resistance sens and maximum background on the speaker. If there is a change in the background when you press your finger for a second, then the key and the opamp work, then we connect the RX coils with the circuit capacitor in parallel, the capacitor on the TX coil in series, put one coil on top of the other and start reducing to 0 according to the minimum AC reading on the first leg of the amplifier U1A. Next, we take something large and iron and check whether there is a reaction to the metal in the dynamics or not. Let's check the voltage at u2B (7th output), it should be a trash regulator, change + - a couple of volts. If not, the problem is in this stage of the op-amp. To start checking the board, turn off the coils and turn on the power.

1. There should be a sound when the sens regulator is set to maximum resistance, touch the PX with your finger - if there is a reaction, all the opamps work, if not - check with your finger starting from u2 and change (examine the strapping) of the non-working op-amp.

2. The operation of the generator is checked by the frequency meter program. Solder the plug from the headphones to pin 12 of the CD4013 (561TM2) prudently soldering p23 (so as not to burn the sound card). Use In-lane in the sound card. We look at the generation frequency, its stability is at 8192 Hz. If it is strongly displaced, then it is necessary to solder the capacitor c9, if even after it is not clearly distinguished and / or there are many frequency bursts nearby, we replace the quartz.

3. Checked amplifiers and generator. If everything is in order, but still does not work, change the key (CD 4066).

Which coil resonance to choose

When the coil is connected to series resonance, the current in the coil and the overall consumption of the circuit increase. The target detection distance is increased, but this is only on the table. On real ground, ground will feel stronger the more pump current in the coil. It is better to turn on parallel resonance, and to raise the flair with input stages. And the batteries last a lot longer. Despite the fact that series resonance is used in all branded expensive metal detectors, Sturm needs exactly parallel. In imported, expensive devices, there is a good ground detuning circuitry, therefore, in these devices, serial can be enabled.

What capacitors are better to install in the circuit metal detector

The type of capacitor connected to the coil has nothing to do with it, and if you experimentally changed two and saw that the resonance is better with one of them, then just one of the supposedly 0.1 uF actually has 0.098 uF, and the other 0.11. Here is the difference between them in terms of resonance. I used Soviet K73-17 and green imported pillows.

How to set coil resonance metal detector

The coil, as the best option, is obtained from plaster floats glued with epoxy from the ends to the size you need. Moreover, its central part with a piece of the handle of this very grater, which is processed to one wide ear. On the bar, on the contrary, there is a fork of two fastening lugs. This solution solves the problem of coil deformation when tightening the plastic bolt. The grooves for the windings are made with an ordinary burner, then zeroing and filling. From the cold end of the TX, let's leave 50 cm of wire, which is not initially poured, but twist a small coil out of it (3 cm in diameter) and place it inside the RX, moving and deforming it within small limits, you can achieve an exact zero, but doing this better outdoors, placing the coil near the ground (as in the search) with the GEB turned off, if any, then finally fill with resin. Then the detuning from the ground works more or less tolerably (with the exception of highly mineralized soil). Such a coil turns out to be light, durable, little subject to thermal deformation, and processed and painted is very pretty. And one more observation: if the metal detector is assembled with ground balance (GEB) and with the central position of the resistor slider set to zero with a very small washer, the GEB adjustment range is + - 80-100 mV. If you set zero with a large object, a coin of 10-50 kopecks. the adjustment range increases to +- 500-600 mV. Do not chase the voltage in the process of tuning the resonance - I have about 40V at 12V with a series resonance. In order for discrimination to appear, we turn on the capacitors in the coils in parallel (serial connection is necessary only at the stage of selecting conders for resonance) - there will be a lingering sound on ferrous metals, and a short one on non-ferrous metals.

Or even easier. We connect the coils in turn to the transmitting TX output. We tune one into resonance, and after tuning it, the other. Step by step: Connected, parallel to the coil, poked variable volts with a multimeter at the limit, also soldered a capacitor 0.07-0.08 microfarads in parallel to the coil, we look at the readings. Let's say 4 V - very weak, not in resonance with the frequency. They poked in parallel with the first capacitor of the second small capacitance - 0.01 microfarads (0.07 + 0.01 = 0.08). We look - the voltmeter has already shown 7 V. Excellent, let's increase the capacitance, connect it to 0.02 uF - we look at the voltmeter, and there it is 20 V. Great, we go further - we will still add a couple of thousand capacitance peaks. Yeah. Already started to fall, roll back. And so to achieve the maximum readings of the voltmeter on the metal detector coil. Then similarly with the other (receiving) coil. Adjust to maximum and plug back into the receiving jack.

How to zero metal detector coils

To adjust zero, we connect the tester to the first leg of the LF353 and gradually begin to compress and stretch the coil. After filling with epoxy, the zero will definitely run away. Therefore, it is not necessary to fill the entire coil, but leave room for adjustment, and after drying, bring it to zero and fill it completely. Take a piece of twine and tie half of the coil with one turn to the middle (to the central part, the junction of two coils), insert a piece of stick into the twine loop and then twist it (pull the twine) - the coil will shrink, catching the zero, soak the twine with glue, after almost complete drying again correct the zero by turning the wand a little more and pour the twine completely. Or more simply: The transmitter is fixed in plastic motionlessly, and the receiver is placed on the first one by 1 cm, such as wedding rings. The first output of U1A will be squeaking 8 kHz - you can control it with an AC voltmeter, but it's better just with high-impedance headphones. So, the receiving coil of the metal detector must either be pushed forward or moved from the transmitting coil until the squeak at the output of the op-amp subsides to a minimum (or the voltmeter readings drop to several millivolts). Everything, the coil is brought together, we fix it.

What is the best wire for search coils

The wire for winding the coils does not matter. Anyone will go from 0.3 to 0.8, you still have to select a little capacity to tune the circuits to resonance and to a frequency of 8.192 kHz. Of course, a thinner wire is quite suitable, just the thicker it is, the better the quality factor and, as a result, the flair is better. But if you wind 1 mm, it will be quite heavy to carry. On a sheet of paper, draw a rectangle 15 by 23 cm. Set aside 2.5 cm from the upper left and lower corners, and connect them with a line. We do the same with the upper and lower right corners, but set aside 3 cm each. In the middle of the lower part, put a dot and a dot on the left and right at a distance of 1 cm. We take plywood, apply this sketch and drive carnations into all points indicated. We take the wire PEV 0.3 and wind 80 turns of wire. But to be honest, it doesn't matter how many turns. Anyway, the frequency of 8 kHz will be set to resonance with a capacitor. How much they wound - so much they wound. I wound 80 turns and a capacitor of 0.1 microfarads, if you wind, let's say 50, you will have to put the capacitance, respectively, somewhere around 0.13 microfarads. Further, without removing from the template, we wrap the coil with a thick thread - like how wire harnesses are wrapped. After we cover the coil with varnish. When dry, remove the coil from the template. Then comes the winding of the coil with insulation - fum tape or electrical tape. Next - winding the receiving coil with foil, you can take a tape of electrolytic capacitors. The TX coil can be left unshielded. Don't forget to leave a 10mm BREAK in the screen, in the middle of the coil. Next comes the winding of the foil with tinned wire. This wire, together with the initial contact of the coil, will be our mass. And finally, winding the coil with electrical tape. The inductance of the coils is about 3.5mH. The capacitance is about 0.1 microfarads. As for filling the coil with epoxy, I did not fill it at all. I just wrapped it tightly with duct tape. And nothing, I spent two seasons with this metal detector without changing the settings. Pay attention to the moisture insulation of the circuit and search coils, because you have to mow on wet grass. Everything must be sealed - otherwise moisture will get in and the setting will float. Sensitivity will deteriorate.

What parts and what can be replaced

transistors:
BC546 - 3pcs or KT315.
BC556 - 1pc or KT361
Operatives:

LF353 - 1pc or change to the more common TL072.
LM358N - 2pcs
Digital ICs:
CD4011 - 1pc
CD4066 - 1pc
CD4013 - 1pc
Resistors, power 0.125-0.25 W:
5.6K - 1pc
430K - 1pc
22K - 3pcs
10K - 1pc
390K - 1pc
1K - 2pcs
1.5K - 1pc
100K - 8pcs
220K - 1pc
130K - 2pcs
56K - 1pc
8.2K ​​- 1pc
Resistors variable:
100K - 1pc
330K - 1pc
Capacitors non-polar:
1nF - 1pc
22nF - 3pcs (22000pF = 22nF = 0.022uF)
220nF - 1pc
1uF - 2pcs
47nF - 1pc
10nF - 1pc
Electrolytic Capacitors:
220uF at 16V - 2pcs

The speaker is tiny.
Quartz resonator at 32768 Hz.
Two super-bright LEDs of different colors.

If you cannot get imported microcircuits, here are domestic analogues: CD 4066 - K561KT3, CD4013 - 561TM2, CD4011 - 561LA7, LM358N - KR1040UD1. The LF353 chip has no direct analogue, but feel free to put LM358N or better TL072, TL062. It is not at all necessary to install an operational amplifier - LF353, I just raised the gain by U1A by replacing the resistor in the negative feedback circuit 390 kOhm with 1 mOhm - the sensitivity increased significantly by 50 percent, although after this replacement it went zero, I had to glue it to the coil in a certain place tape a piece of aluminum plate. The Soviet three kopecks feels through the air at a distance of 25 centimeters, and this is when powered by 6 volts, the current consumed without indication is 10 mA. And do not forget about the panels - the convenience and ease of setup will increase significantly. Transistors KT814, Kt815 - in the transmitting part of the metal detector, KT315 in the ULF. Transistors - 816 and 817, it is desirable to choose with the same gain. Replaceable with any appropriate structure and capacity. A special watch quartz is installed in the metal detector generator at a frequency of 32768 Hz. This is the standard for absolutely all quartz resonators that are in any electronic and electromechanical watches. Including wrist and cheap Chinese wall / desktop. PCB archives for the variant and for (manual ground balance variant).

What determines the depth of the search for goals

The larger the diameter of the metal detector coil, the deeper the flair. In general, the depth of target detection with a given coil depends primarily on the size of the target itself. But with an increase in the diameter of the coil, there is a decrease in the accuracy of object detection and even sometimes the loss of small targets. For objects the size of a coin, this effect is observed when the coil size is increased above 40 cm. In summary: a large search coil has a greater detection depth and greater capture, but detects the target less accurately than a small one. The large coil is ideal for finding deep and large targets such as treasures and large objects.

According to the shape of the coil are divided into round and elliptical (rectangular). An elliptical metal detector coil has better selectivity than a round one, because it has a smaller magnetic field and fewer foreign objects fall into its field of action. But the round one has a greater detection depth and better sensitivity to the target. Especially on weakly mineralized soils. The round coil is most commonly used when searching with a metal detector.

Coils with a diameter of less than 15 cm are called small, coils with a diameter of 15-30 cm are called medium and coils over 30 cm are called large. A large coil generates a larger electromagnetic field, so it has a greater detection depth than a small one. Large coils generate a large electromagnetic field and, accordingly, have a large detection depth and search coverage. Such coils are used to view large areas, but when using them, a problem may arise on heavily littered areas because several targets can fall into the field of action of large coils at once and the metal detector will react to a larger target.

The electromagnetic field of a small search coil is also small, so with such a coil it is best to search in areas heavily littered with all sorts of small metal objects. The small coil is ideal for detecting small objects, but has a small coverage area and relatively shallow detection depth.

Medium coils work well for general purpose searches. This size of the searchcoil combines sufficient search depth and sensitivity to targets with different sizes. I made each coil with a diameter of about 16 cm and put both of these coils in a round stand from under an old 15" monitor. In this version, the search depth of this metal detector will be as follows: an aluminum plate 50x70 mm - 60 cm, a M5-5 cm nut, a coin - 30 cm, bucket - about a meter These values ​​​​are obtained in the air, in the ground it will be 30% less.

Power supply of the metal detector

Separately, the metal detector circuit draws 15-20 mA, with the coil connected + 30-40 mA, totaling up to 60 mA. Of course, depending on the type of speaker and LEDs used, this value may vary. The simplest case - power was taken by 3 (or even two) series-connected lithium-ion batteries from mobile phones at 3.7V and when charging discharged batteries, when we connect any power supply to 12-13V, the charge current starts from 0.8A and drops to 50mA in an hour, and then you don’t need to add anything at all, although a limiting resistor certainly doesn’t hurt. As in general, the simplest option is a 9V crown. But keep in mind that a metal detector will eat it in 2 hours. But for customization, this power option is the most it. Krona under any circumstances will not give out a large current that can burn something in the board.

Homemade metal detector

And now a description of the metal detector assembly process from one of the visitors. Since I only have a multimeter from the devices, I downloaded the virtual laboratory Zapisnykh O.L. from the Internet. I assembled an adapter, a simple generator and drove an oscilloscope to idle. It looks like it's showing a picture. Then I started looking for radio components. Since prints are mostly laid out in the “lay” format, I downloaded “Sprint-Layout50”. I found out what laser-ironing technology for manufacturing printed circuit boards is and how to etch them. Removed the fee. By this time, all microcircuits were found. What I did not find in my shed, I had to buy. I started soldering jumpers, resistors, microcircuit sockets, and quartz from a Chinese alarm clock to the board. Periodically checking the resistance on the power rails so that there is no snot. I decided to start by assembling the digital part of the device, as the easiest. That is, a generator, a divider and a switch. Collected. I installed a generator chip (K561LA7) and a divider (K561TM2). Used microcircuits, torn out from some boards found in a shed. I applied 12V power while controlling the current consumption by an ammeter, 561TM2 became warm. Replaced 561TM2, powered up - zero emotions. I measure the voltage on the legs of the generator - on legs 1 and 2 12V. I change 561LA7. I turn it on - at the output of the divider, there is generation on the 13th leg (I watch it on a virtual oscilloscope)! The picture is really not so hot, but in the absence of a normal oscilloscope, it will do. But there is nothing on 1, 2 and 12 legs. So the generator is working, you need to change TM2. I installed the third divider chip - there is beauty at all outputs! For myself, I concluded that you need to solder the microcircuits as carefully as possible! This is the first step in the construction.

Now we are setting up the metal detector board. The "SENS" regulator did not work - the sensitivity, I had to throw out the capacitor C3 after that the sensitivity adjustment worked as it should. I did not like the sound that occurs in the extreme left position of the "THRESH" regulator - the threshold, got rid of this by replacing the resistor R9 with a chain of series-connected 5.6 kΩ resistor + 47.0 uF capacitor (negative terminal of the capacitor on the transistor side). While there is no LF353 chip, instead of it, I put LM358, with it the Soviet three kopecks feel in the air at a distance of 15 centimeters.

I included the search coil for transmission as a series oscillatory circuit, and for reception as a parallel oscillatory circuit. I set up the transmitting coil first, connected the assembled sensor structure to the metal detector, the oscilloscope parallel to the coil and selected the capacitors according to the maximum amplitude. After that, I connected the oscilloscope to the receiving coil and picked up the capacitors on the RX according to the maximum amplitude. Setting the circuits to resonance takes, with an oscilloscope, several minutes. The TX and RX windings each contain 100 turns of wire with a diameter of 0.4. We start mixing on the table, without the case. Just to have two hoops with wires. And in order to make sure that it works and that it is possible to mix in general, we will separate the coils from each other by half a meter. Then zero will be exactly. Then, having overlapped the coils by about 1 cm (like wedding rings), move - move apart. The zero point can be quite precise and not easy to catch right away. But she is.

When I raised the gain in the RX path of the MD, it began to work unstably at maximum sensitivity, this manifested itself in the fact that after passing over the target and detecting it, a signal was issued, but it continued even after there was no longer any target in front of the search coil, this manifested itself in the form of intermittent and oscillating sound signals. With the help of an oscilloscope, the reason for this was also discovered: when the speaker is operating and there is a slight drop in the supply voltage, "zero" goes away and the MD circuit goes into a self-oscillating mode, which can only be exited by coarsening the sound signal threshold. This didn’t suit me, so I put a KR142EN5A + extra bright white LED on the power supply to raise the voltage at the output of the integral stabilizer, I didn’t have a stabilizer for a higher voltage. Such an LED can even be used to illuminate the search coil. The speaker connected to the stabilizer, after that the MD immediately became very obedient, everything started to work as it should. I think Volksturm is really the best homemade metal detector!

Recently, this refinement scheme has been proposed, which will turn the Volksturm S into the Volksturm SS + GEB. Now the device will have a good discriminator, as well as metal selectivity and ground detuning, the device is soldered on a separate board and connected instead of capacitors c5 and c4. Scheme of completion and in the archive. Special thanks for the information on assembling and setting up the metal detector to everyone who took part in the discussion and modernization of the circuit, especially Elektrodych, fez, xxx, slavake, ew2bw, redkii and other radio amateur colleagues helped in the preparation of the material.