A simple circuit of a metal detector for MS K176la7. A very simple and reliable metal detector based on the K561LA7 chip. Location of SMD parts on the board

After reading a little on amateur radio forums production of metal detectors, found that most people collecting metal detectors, in my opinion, are unfairly written off beat metal detectors- so called BFO metal detectors. Allegedly, this is the technology of the last century and “children’s toys.” — Yes, this is a simple and unprofessional device that requires certain skills and experience in handling. It does not have a clear metal selectivity and requires adjustment during operation. However, it is also possible to perform a successful search under certain circumstances. As an option - beach search- perfect option for a metal detector on beats.

Place to search with a metal detector.

You need to go with a metal detector where people lose something. I'm lucky to have a place like this. Not far from my house there is an abandoned river sand quarry, where people constantly relax in the summer, drinking and swimming in the river. It’s clear that they are constantly losing something. In my opinion, best place for searching with a metal detectorBFO I can't think of it. Lost items are instantly buried at a shallow depth in dry sand and it is almost impossible to find them manually. Some kind of mysticism. I remember when I was a child I dropped my apartment keys in the sand there. Here I am standing, the keys fell here, but no matter how much I dug up that area, it was all to no avail. They literally fell through the ground. Just an enchanted place. At the same time, on this “golden” beach, I constantly found other people’s keys, lighters, coins, jewelry and phones in the sand. And on my last trip with a metal detector, I found a woman’s thin gold ring. It was almost at the surface, slightly sprinkled with sand. Perhaps it was just luck. Actually, it was for this beach that I made my metal detector.

Advantages of a beat metal detector.

Why exactly BFO? - First of all, this is the most simple metal detector option. Secondly, it has at least some signal dynamics depending on the properties of the object. Not really pulse metal detector- “beeping” for everything the same. I in no way want to belittle advantages of a pulse metal detector. This is also a wonderful device, but it is not suitable for a beach littered with corks and foil. Many will say that a beating metal detector does not distinguish the properties of an object, howls and buzzes at everything the same. However, it is not. After practicing on the beach for a couple of days, I became quite good at identifying foil as a sharp and profound change in frequency. Beer bottle caps cause a strictly defined frequency change that needs to be remembered. But the coins emit a weak, “point” signal - a subtle change in frequency. All this comes with experience, patience and good hearing. Beat metal detector- it’s still "auditory" metal detector. The analyzer and signal processor here is a person. For this reason, you must search on headphones, and not on the speaker. Moreover, the best option is large headphones, not earplugs.

Metal detector design.

Structurally I I decided to make a metal detector foldable and compact. So that it fits into a regular bag, so as not to attract the attention of “normal” people. Otherwise, when you get to the search site, you look like an “alien” or a scrap metal collector. For this purpose, I bought the smallest (two-meter five-legged) telescopic rod in the store. Left three knees. The result was a fairly compact folding base, on which I assembled my metal detector.

The entire electronic unit was assembled in the 60x40 plastic wiring box I already loved. The end cap, the power compartment partition and the power compartment cover were also made from its plastic. The parts were glued together with superglue and mounted on M3 bolts. Fastening metal detector electronic unit to the rod is made in the form of a metal bracket, which is inserted into place of the fishing reel with fishing line and secured with the standard nut of the rod. The result is an excellent lightweight and durable design. On the outside of the unit there is a power button, a coil connection socket (a five-pin socket from a “grandfather’s” tape recorder), a frequency regulator and a headphone jack.

Metal detector circuit board was made on site by laying out the paths with a waterproof marker. For this reason, unfortunately, I cannot provide a seal. Surface mounting - no holes - "lazy" - my favorite. It is also important, after assembling the board, to cover it with any varnish to protect it from moisture and debris. In field conditions this is very important. For example, I lost one day because some debris got inside under the microcircuit. The metal detector just stopped working. And I had to return home, disassemble it, blow it out and open the board with varnish.

Diagram of a beat metal detector.

The circuit itself (see below) was redesigned and optimized by me from two metal detector circuits. This is "" - Radio magazine, 1987, No. 01, pp. 4, 49 and " High sensitivity metal detector" - Radio magazine, 1994, No. 10, page 26.

The result is a simple and functional circuit that provides stable low-frequency resulting beats - what is needed to determine by ear the slightest changes in frequency.

The stability and sensitivity of the metal detector are ensured by the following circuit solutions:

The reference and measuring generators are separated- made in separate microcircuit packages - DD1 and DD2. At first glance, this is wasteful - only one logical element of the microcircuit package is used out of four. That is, yes, the reference generator is assembled on only one logical element of the microcircuit. The remaining three logical elements of the microcircuit are not used at all. The measuring generator is built in exactly the same way. It would seem pointless not to use free logic gates microcircuit housings. However, this is precisely what makes a lot of sense. And it consists in the fact that if, for example, you assemble two generators in one microcircuit package, they will synchronize each other at close frequencies. It will not be possible to obtain the slightest changes in the resulting frequency. In practice, this will look like a sharp change in frequency only when a massive metal object is close to the measuring coil. In other words, sensitivity sharply decreases. Metal detector does not react to small objects. The resulting frequency seems to “stick” to zero—up to a certain point, there are no beats at all. They also say - “ dumb metal detector", "dull sensitivity". By the way " Metal detector on a chip" - Radio magazine, 1987, No. 01, pp. 4, 49 is built on just one microcircuit at all. This effect of frequency synchronization is very noticeable there. It is completely impossible for him to search for coins and small objects.

Also, both generators must be shielded with separate small screens made of tin. This increases by an order of magnitude stability and sensitivity of the metal detector as a whole. It is enough to simply solder small partitions made of tin at minus between the generator chips to ensure that the parameters of the metal detector are improved. How better screen- the better the sensitivity (the influence of the generators on each other is weakened and plus protection from external influences on the frequency).

Electronic tuning.

Comparator on DD3.2 – DD3.4.

This circuit element converts the sinusoidal signal from the output of the DD3.1 mixer into rectangular pulses of double frequency.

Firstly, rectangular pulses are clearly audible at hertz frequencies as clear clicks. While a sinusoidal signal of hertz frequencies is already difficult to distinguish by ear.

Secondly, doubling the frequency allows the adjustment to come closer to zero beats. As a result, by adjusting you can achieve a “clicking” sound in the headphones, the change in frequency of which can already be detected when you bring a small coin to the coil at a distance of 30 cm.

Generator power stabilizer.

Naturally, in this circuit, the supply voltage noticeably affects the frequency of generators DD1.1 and DD2.1 metal detector. Moreover, each of the generators is affected differently. As a result, with the battery draining a little The beat frequency of the metal detector also “floats”. To prevent this, a five-volt stabilizer DA1 was introduced into the circuit to power generators DD1.1 and DD2.1. As a result, the frequency stopped “floating”. However, it should be said that on the other hand, due to the five-volt power supply of the generators, several The sensitivity of the metal detector has decreased generally. Therefore, this option should be considered optional and, if desired, generators DD1.1 and DD2.1 can be powered from the crown without a DA1 stabilizer. You just have to adjust the frequency manually more often using a regulator.

Metal detector coil design.

(See diagram below).

Since this not a pulse metal detector, butBFO, then the search coil (L2) is not afraid of metal objects in its design. We don't need a plastic bolt. That is, we can safely use a metal (but only open!) frame and a regular metal bolt for the hinge to make it. Subsequently, when setting up the circuit, all the influences of the metal in the structure will be brought to zero by the tuning core of the L1 coil. The L2 coil itself contains 32 turns of PEV or PEL wire with a diameter of 0.2 - 0.3 mm. The diameter of the coil should be about 200 mm. It is convenient to wind on a small plastic conical bucket. The resulting turns are completely wrapped with electrical tape and tied with thread. Next, this entire structure is wrapped in foil (cooking foil for baking). Tinned wire is wound on top of the foil in several turns around the entire perimeter of the coil. This wire will be the output of the coil's foil screen. Once again everything is wrapped together with electrical tape. The coil itself is ready.

The frame on which the reel will be located and with which it will be attached to the fishing rod is made of springy steel (not soft) wire 3-4 mm. It actually consists of three parts (see figure) - two twisted wire loops of the hinge, which will be connected by a bolt to each other and a wire ring threaded into the tube from the dropper (the ring should not be a closed turn).

This entire structure, together with the finished wire spool, is also tied together with threads and electrical tape.

The joint itself with the reel is attached to the rod by tying it with nylon threads and gluing it with epoxy resin.

It is advisable not to wet the coil during the search process, and especially not to use it for underwater searching. It is not airtight. Moisture that gets inside can destroy it over time.

Coil L1 (see diagram) is wound on a frame from a small-sized radio receiver with a metal screen and a tuning core. The coil contains 65 turns of PEV wire with a diameter of 0.06mm

Me and Diode. © site.

Scheme of a simple and affordable metal detector based on the K561LA7 chip, also known as CD4011BE. Even a novice radio amateur can assemble this metal detector with his own hands, but despite the spaciousness of the circuit, it has quite good characteristics. The metal detector is powered by a regular crown, the charge of which will last for a long time, since the power consumption is not large.

The metal detector is assembled on just one K561LA7 (CD4011BE) chip, which is quite common and affordable. To configure, you need an oscilloscope or a frequency meter, but if you assemble the circuit correctly, then these devices will not be needed at all.

Metal detector circuit

Metal detector sensitivity

As for the sensitivity, it is not bad enough for such a simple device, say, it sees a metal can from a can at a distance of up to 20 cm. A coin with a face value of 5 rubles, up to 8 cm. When a metal object is detected, a tone will be heard in the headphones, the closer the coil is to object, the stronger the tone. If the object has a large area, say, like a sewer hatch or a pan, then the detection depth increases.

Metal detector components

• You can use any low-frequency, low-power transistors, such as those on KT315, KT312, KT3102 or their foreign analogues VS546, VS945, 2SC639, 2SC1815
• The microcircuit is K561LA7, it can be replaced with an analog CD4011BE or K561LE5
• Low-power diodes such as kd522B, kd105, kd106 or analogues: in4148, in4001 and the like.
• Capacitors 1000 pF, 22 nF and 300 pF should be ceramic, or better yet, mica ones, if available.
• Variable resistor 20 kOhm, you need to take it with the switch or the switch separately.
• Copper wire for the coil, suitable for PEL or PEV with a diameter of 0.5-0.7 mm
• Headphones are ordinary, low-impedance.
• The battery is 9 volts, the crown is quite suitable.

A little information:

The metal detector board can be placed in a plastic case from automatic machines, you can read how to make it in this article:. In this case, a junction box was used))

If you do not confuse the part values, if you solder the circuit correctly and follow the instructions to wind the coil, then the metal detector will work immediately without any special settings.

If, when you turn on the metal detector for the first time, you do not hear a squeak in the headphones or a change in frequency when adjusting the “FREQUENCY” regulator, then you need to select a 10 kOhm resistor in series with the regulator and/or a capacitor in this generator (300 pF). Thus, we make the frequencies of the reference and search generators the same.

When the generator is excited, whistling, hissing or distortion appears, solder a 1000 pF (1nf) capacitor from the sixth pin of the microcircuit to the case, as shown in the diagram.

Using an oscilloscope or frequency meter, look at the signal frequencies at pins 5 and 6 of the K561LA7 microcircuit. Achieve their equality using the above-described adjustment method. The operating frequency of generators can range from 80 to 200 kHz.

A protective diode (any low-power one) is needed to protect the microcircuit if, for example, you connect the battery incorrectly, and this happens quite often.))

Metal detector coil

The coil is wound with PEL or PEV wire 0.5-0.7 mm on a frame, the diameter of which can be from 15 to 25 cm and contains 100 turns. The smaller the coil diameter, the lower the sensitivity, but the greater the selectivity of small objects. If you are going to use a metal detector to search for ferrous metal, it is better to make a larger diameter coil.

The coil can contain from 80 to 120 turns; after winding, it is necessary to wrap it tightly with electrical tape as shown in the diagram below.

Now you need to wrap some thin foil around the top of the electrical tape, food grade or chocolate foil will do. You don’t need to wrap it all the way, but leave a couple of centimeters, as shown below. Please note that the foil is wound carefully; it is better to cut even strips 2 centimeters wide and wrap the coil like electrical tape.

Now wrap the coil tightly with electrical tape again.

The coil is ready, now you can attach it to a dielectric frame, make a rod and assemble everything into a heap. The rod can be soldered from polypropylene pipes and fittings with a diameter of 20 mm.

To connect the coil to the circuit, a double shielded wire (screen to the body) is suitable, for example the one that connects a TV to a DVD player (audio-video).

How a metal detector should work

When turned on, use the “frequency” regulator to set the headphones low frequency hum, when approaching the metal, the frequency changes.

The second option, so that there is no buzzing in the ears, is to set the beats to zero, i.e. combine two frequencies. Then there will be silence in the headphones, but as soon as we bring the coil to the metal, the frequency of the search generator changes and a squeak appears in the headphones. The closer to the metal, the higher the frequency in the headphones. But the sensitivity with this method is not great. The device will react only when the generators are strongly detuned, for example, when brought close to a jar lid.

Location of DIP parts on the board.

Location of SMD parts on the board.

Metal detector board assembly

Fragments from the book “Do-it-yourself metal detectors. How to search to find coins, jewelry, treasures.” Authors S. L. Koryakin-Chernyak and A. P. Semyan.

Continuation

Read the beginning here:

3.1. Compact metal detector based on K175LE5 chip

Purpose

The metal detector is designed to search for metal objects in the ground. It can also be used to determine the location of fittings and hidden wiring during construction work in the house.

Circuit diagram

The diagram of a compact metal detector based on a K175LE5 microcircuit is shown in Fig. 3.1, a. It contains two oscillators (reference and search). The search generator is assembled on elements DD1.1, DD1.2, and the reference generator is assembled on elements DD1.3 and DD1.4.

The frequency of the search generator made on elements DD1.1 and DD1.2 depends on:

• from the capacitance of capacitor C1;
• from the total resistance of the tuning and variable resistors R1 and R2.

Variable resistor R2 smoothly changes the frequency of the search generator in the frequency range set by trimming resistor R1. The frequency of the generator on elements DD1.3 and DD1.4 depends on the parameters of the oscillatory circuit L1, C2.

Signals from both generators are supplied through capacitors C3 and C4 to a detector made according to a voltage doubling circuit on diodes VD1 and VD2.

The load of the detector is the BF1 headphones, on which the difference signal is isolated in the form of a low-frequency component, which is converted by the headphones into sound.

A capacitor C5 is connected in parallel with the headphones, which shunts them at a high frequency. When the search coil L1 approaches a metal object, the frequency of the generator on elements DD1.3, DD1.4 changes, as a result the tone of the sound in the headphones changes. This feature is used to determine whether a metal object is in the search area.

Parts used and options for replacing elements

Trimmer resistor R1 type SP5-2, variable resistor R2 - SPO-0.5. It is acceptable to use other types of resistors in the circuit, preferably small ones.

Electrolytic capacitor C6 type K50-12 - for a voltage of at least 10 V. The remaining permanent capacitors are type KM-6.

Coil L1 is placed in a ring with a diameter of 200 mm, bent from a copper or aluminum tube with an internal diameter of 8 mm. There should be a small insulated gap between the ends of the tube so that there is no short-circuited turn. The coil is wound with PELSHO 0.5 wire.

Headphones TON-1, TON-2 can be used as BF1 headphones.

The metal detector is powered by a Krona battery or other types of 9 V batteries.

In the metal detector circuit, the K176LE5 microcircuit can be replaced with K176LA7, K176PU1, K176PU2, K561LA7, K564LA7, K561LN2 microcircuits.

Device installation

Parts of the device, except the inductor, power supply and headphones, can be placed on printed circuit board, cut from foil fiberglass laminate 1 mm thick (Fig. 3.1, b). It is possible to use another type of printed circuit board.

A handle made of a metal tube is attached to one end of the connector, and a metal ring with coil L1 is attached to the other end using an adapter made of insulating material.

The general view of the device is shown in Fig. 3.1, d, and the placement of device elements is in Fig. 3.1, c.

Settings

Before setting up the metal detector, the tuning and variable resistors must be placed in the middle position and the SB1 contacts must be closed. By moving the slider of the adjusted resistor R1, achieve the lowest tone in the headphones.

If there is no sound, you should select the capacitance of capacitor C2. If malfunctions occur in the operation of the metal detector, a capacitor with a capacity of 0.01...0.1 µF should be soldered between pins 7 and 14 of the DD1 microcircuit.

Source
Yavorsky V. Metal detector on K176LE5. // Radio, 1999, No. 8, p. 65.

From book S. L. Koryakin-Chernyak, A. P. Semyan. " "

Continue reading

Homemade metal detector based on K176LA7 chip

Many have already written to us asking us to post some simple diagram homemade metal detector. And today, in my free time after passing the exam, it appears on the site metal detector circuit with 3 chips- K176LA7.

Previously, we reviewed some metal detector circuits on our website.

Now let’s move on to the topic of the article by clicking the more details button.

The scheme itself:

L1 – wind up on a 3-section frame with a tuning core (IF circuit of the Sokol-40 radio receiver) and placed in an armored magnetic circuit with a diameter of 8.8 mm made of 600NN ferrite. The coil contains 200 turns of PEV-2 wire 0.08...0.09 mm.

I used a random IF coil with an aluminum shield.

L2 - 18 pieces of wire in reliable insulation are threaded into an aluminum thin-walled tube with a diameter of 6...9 mm and a length of about 950 mm. Then the tube is bent on a mandrel with a diameter of approximately 15 cm, and the pieces of wire are connected to each other in series. The inductance of such a coil should be approximately 350 μH. The ends of the tube are left open, but one of them is connected with a common wire. I used a rubber hose with a metal braid inside which I pulled through a solid wire in varnish insulation using tweezers. The tweezer jaws should be wrapped with electrical tape to avoid damaging the insulation. You need to make sure that the winding is as fixed as possible, otherwise the metal detector will trigger falsely.

The board is placed in a metal, necessarily non-magnetic case.

The wires from the board to the L2 coil must be shielded.

When starting to set up the metal detector, set the capacitor handle to the middle position and, by rotating the tuning core L1, achieve zero beats in the phones. The setting can be considered correct if, when turning the variable capacitor knob slightly, the phone appears sound signal low frequency. The adjustment should be made at a distance of at least a meter from massive metal objects. In my version, it turned out that the sensitivity of the metal detector increased if the core of the trimming coil was screwed into it completely, and by rotating variable capacitor it was possible to configure the absence of beats in two places. At the same time, the sound in the headphones at full volume was quiet. If the sound does not appear at all, then you need to use an oscilloscope to check the presence of a U-shaped signal at pins 4 of DD1 and DD2, and a mixture of signals at pins 11 and 8 of DD3. In the original, instead of R3 3kOhm, 300kOhm is indicated, but with such resistance the sound did not appear in the headphones. Due to lack of availability, instead of 5600pF capacitors, I used 4700pF.

In practice, this metal detector has proven itself well. They can detect a coin at a depth of up to 10 cm, a pan up to 30 cm, a sewer hatch up to 60 cm.

The main disadvantage: due to changes in ambient temperature, it is necessary to adjust the zero beat frequency with a variable capacitor. I would like to see proposals for eliminating this shortcoming in this scheme (preferably with examples).

Note:

1) I recommend pour epoxy resin into the search coil and let it harden. This will prevent false positives of the metal detector, since during the search you sometimes have to touch various objects with the coil, which causes displacement of the turns inside the coil. Instead of epoxy resin, you can pour melted wax or plasticine, but then you need to take care that it does not leak out in hot weather. Paraffin should not be poured in, as when it hardens it becomes brittle and not elastic.

2)R3-30kOhm you need to replace it with 300 kOhm and adjust the frequency of the model generator until confident loud clicks appear in the headphones. The lower the click frequency, the more sensitive the metal detector. I manage to detect a one-kopeck coin from the times of the USSR at a depth of up to 10 cm, if the coin lies horizontally to the surface.
If you set the click tone to high, this allows you to detect objects by changing the tone of the signal.

I don’t know what this is connected with, but after reassembling another similar metal detector, for a long time I could not get sound to appear in the headphones. Removing capacitor C7 from the circuit helped (replacing it with another one or with a smaller capacity did not work). True, the sound volume became a little lower, but this made it possible to do without a variable resistor - a volume control. The sensitivity of the metal detector remained at the proper level.

In a radio store you can inexpensively (31 rubles PMR) buy a ready-made plastic case measuring 65x115x45 mm in which you can freely place the circuit of this metal detector. You can screen the circuit like this: cut out a “shirt” from cardboard, wrap it in foil, fasten its edges to the cardboard, then attach the conductor with a stapler and connect it to the common wire (minus).

Searching for treasures, ancient relics and other interesting things is a fairly popular hobby for many, along with fishing or hunting. This type of recreation can also be considered active, and for some, a metal detector is quite a good tool for making money, because in the ground you can find quite a large amount of ferrous metals, which are valued today. After all, there is a proverb that “we walk on money.”

In stores, even for a metal detector that is not very powerful, they sometimes charge decent money. In this article we'll talk about how you can assemble a metal detector with your own hands. This requires minimal skills in working with electronics and a small investment (in comparison with buying a new metal detector).

Materials and tools for assembly:
- K561LA7 microcircuit or its equivalent;
- low-power low-frequency transistor (KT315, KT312, KT3102 are suitable, analogues: BC546, BC945, 2SC639, 2SC1815 and so on)
- any low-power diode (for example kd522B, kd105, kd106...);
- three variable resistors (4.7 kOm, 6.8 kOm, 10 kOm with switch);
- five fixed resistors (22 Om, 4.7 kOm, 1.0 kOm, 10 kOm, 470 kOm);]
- five ceramic or mica capacitors (1000 pf - 2 pcs., 22 nF - 2 pcs., 300 pf);
- one electrolytic capacitor (100.0 uF x 16V);
- PEV or PEL type wire with a diameter of 0.6-0.8 mm;
- headphones from the player (or any low-impedance ones);
- 9V battery.

Metal detector manufacturing process:

Step one. Housing and appearance devices
Due to the fact that searches often take place among branches, grass or in wet weather, the device must be reliably protected from the influence of all these factors. You can use a soap or shoe polish box as a housing for electronics. The main thing is that the electronic part is reliably protected.

It is important to know that if you do not connect variable resistors(their housing) with a minus board, the device will generate interference. If everything is done correctly and a high-quality coil is made, no problems will arise during the operation of the device. When you turn on the metal detector, a characteristic squeak should immediately appear in your headphones; it should respond to the frequency control knob. If this is not observed, then you need to select a 10 kOhm resistor, which is in series with the regulator, or select a 300 pF capacitor in this generator. As a result, you need to align the frequencies of the search and reference generators.

To determine what frequencies the generator emits, you will need an oscilloscope. In total, the operating frequency can be in the range of 80-200 kHz. Measurements are taken on pins 5 and 6 of the K561LA7 microcontroller.

The system also has a protective diode. It is needed to protect the electronics from the battery being turned on incorrectly.

Step two. Making a search coil
The coils are wound on mandrels with a diameter of about 15-25 cm. A bucket or shuttle made of wire or plywood can be used as a form. The smaller the coil, the less sensitivity it will have, it all depends on the purpose for which the metal detector will be used.

As for the wire, it can be a wire in varnish insulation such as PEV or PEL with a diameter of 0.5 to 0.7 mm. This type of wire can be found in old TVs with picture tubes. In total, the coil contains 100 turns, you can wind from 80 to 120. The whole thing is tightly wrapped with electrical tape on top.

When the coil is wound, a winding of a strip of foil is made on top of it, while you need to leave a section of 2-3 centimeters unwound. Foil can be found in some types of cables; it can also be obtained from chocolate bars by cutting it into pieces.

It is not an insulated wire that is wound on top of the foil, but preferably a tinned one. The beginning of the wire ends up on the coil, and the other end is soldered to the body. The whole thing is again well wrapped with electrical tape on top.

Subsequently, the coil is attached to a dielectric; non-foil PCB is an option. Well, now the reel can be attached to the holder.

To connect the coil to the circuit, you need to use a shielded wire; the screen is connected to the housing. Similar wires can be used to dub music from a tape recorder. You can also use the bass cord to connect various devices to the TV.

Step three. Checking the metal detector
When the device is turned on, a characteristic noise can be heard in the headphones; the frequency must be adjusted using the regulator. When you bring the coil close to the metal, the noise in the headphones will change.

You can also alter the circuit in such a way that the metal detector is silent during operation, and the signal will appear only when metal appears under the coil. In this case, the frequency of the noise will indicate the size of the object and at what depth it is located. But, according to the author, with this approach the sensitivity of the metal detector is greatly reduced, and it only detects very large objects.

To obtain zero beats, you need to combine two frequencies.