How to make a polygraph at home. Do-it-yourself hidden wiring detector, manufacturing diagram and design options. Types of modern search devices and their characteristics

Back in the 19th century, scientists proved that deception and denial of guilt cause a number of physiological changes in the human condition. The first thing that scientists noticed was high blood pressure, sweating on the skin, dry mouth, heavy inhalations and exhalations. Based on these phenomena, scientists, psychologists and physiologists developed a polygraph. Current lie detectors can determine whether a person answered the truth in more than 90% of cases.

The polygraph includes several measuring instruments with recording devices connected to them:

• sensor on an elastic bracelet, which is attached above the elbow, and gives readings about changes in pulse and pressure
• sensor, which is placed at the same level with the chest, to transmit the breathing rhythm to paper
• 2 sensors will be placed on the hands to record changes in the test subject's skin resistance.

Testing is carried out as follows: a person is asked a series of questions, he must give answers to them yes or no. To begin with, they ask light questions that are not related to the incident in order to see what a person’s normal reaction is, then they ask questions that are directly related to the incident. And immediately a deviation from the norm is observed. This is shown in Figure 1.

For a more accurate test of the subject, there is a method with any cards. The test taker is shown 10 cards, of which he must remember only one. Then they are shuffled, and he must answer “no” ten times. It turns out that one time he will still lie. This answer will be recorded and used in a further survey.

In the United States, more than twenty national institutions (this also includes the police, FBI) ​​have had more than 500 lie detectors since 1965. Most private institutions, such as a bank, regularly test their employees with a polygraph. Companies that manufacture lie detectors conduct training courses for subordinates who then work with the lie detector.

How to make a lie detector at home

If you decide to try yourself as a polygraph examiner, but for now you have no desire to buy a lie detector for several thousand dollars. You can purchase it from us, our company sells not only new but also used polygraphs at a price several times cheaper than new ones. You can also try to create it at home. However, basic knowledge of radio electronics is required.

Figure 2 shows a simplified electrical circuit diagram. However, it has high sensitivity, which means that if the test shooter is slightly agitated, the device will deviate.

Figure 3 shows two electrodes, they look like two loops, and are attached to the wrist or arm. When attached to the hand, significant sensitivity will be provided, but there will also be interference.

The sensitivity of the lie detector shown in Figure 2 is changed by resistor R1. A recorder can be connected to the output terminals. All resistors that are in the circuit serve only to protect the transistors from overloads. In the end you will get a good device with which you can do some very fun experiments.

Do-it-yourself polygraph, diagram two

The operating principle of this circuit is as follows: the device amplifies infra-low frequencies, the gain is 399-1199. What exactly the device will do depends on the type of output controller that will capture the output signal. You and I will use it as a “lie detector.”

As described above, thought processes are consistent with physiological changes in state. When a person is worried, the heart rate increases, and the frequency of inhalation and exhalation changes noticeably. It is very clearly possible to register how the resistance of the test subject’s skin changes; after several questions about what he wanted to hide, the resistance changes by 3-5%. To do this, we need two sensors that will be placed on the fingers of one hand of the person being tested. This is shown in Figure 2.

After we have attached the sensors to our fingers and turned on the device, we need to wait about 10 seconds for the transient processes to end. The person being tested should place his hands comfortably and not move them. Next, we ask questions to the examiner, and it is necessary to ask them not quickly, take a break for up to 4 seconds, and after the indicator lights have gone out. In some cases, the LEDs flash after each question, which symbolizes the person’s excitement. We need to give him time to calm down. As an example of test questions, you can use the method described above with cards. Figure three shows a single-sided printed circuit board for a homemade lie detector. The device contains radioelements:

• power from the crown;
• capacitors C1, C5, C6 are ceramic, and the rest are K50-6;
• transistor KT315; and ET361;
• resistors SP3-1B;
• two AL307 LEDs.

When you plan to hang a picture or wall clock, how do you choose the right place for it? You are probably thinking about how the painting will fit into the interior of the room, which wall is best to place it on and how. But have you ever thought that not everywhere you can hammer a nail into the wall and drill a hole for a dowel? It's not about what material your walls are made of, since there is a more significant circumstance - this is the electrical wiring. In order not to damage the wires walled up in the wall, you need to know where they are laid.

There are several ways to find out approximately where the electrical cable runs: you should look at the technical documentation of the apartment and look at the wiring diagram of the electrical network; if there is none, then pay attention to the location of the branch boxes, from which the wires go to sockets and switches. As a rule, smart electricians lay the cable at a right angle.

It’s good when you replaced the old electrical wiring and are aware of its placement, but what if the previous owner of the house was a self-taught electrician and did not follow the basic rules of wiring? There are cases when, in order to save money, the wires are routed along the shortest path: from the boxes diagonally and horizontally - in this case, you cannot do without special means for detecting it.

In stores and radio markets they sell special devices called “Hidden Wiring Detector”. They are cheap (low class) and expensive (high class). A low-class device detects the source of electromagnetic radiation - these are live wires and electrical appliances. High-end detectors are more accurate and functional: their work is aimed at identifying wires directly, even those that are without voltage.

For home use, a simple detector that you can make yourself will be enough for us. As you understand, the simple circuit we have assembled refers to budget devices - therefore, we will not be able to create a high-end device. But a homemade product will help you avoid getting into trouble when performing construction work and at the moment when you decide to decorate your room with a beautiful painting or wall clock. In order to quickly assemble a hidden wiring detector ourselves, we will need three non-scarce radio components, which will not be difficult for us to find.

The main element is the Soviet K561LA7 microcircuit (the detector itself is assembled on it). The microcircuit is sensitive to electromagnetic and static fields emanating from conductors of electrical energy and electronic devices. The microcircuit is protected from increased electrostatic fields by a resistor, which is an intermediate element between the antenna and the IC. The sensitivity of the detector is determined by the length of the antenna. As an antenna, you can use a single-core copper wire 5 to 15 centimeters long. For stable operation and without compromising sensitivity, I chose a length of 8 centimeters. There is one caveat: if the antenna length exceeds the threshold of 10 centimeters, there is a risk of the microcircuit going into self-excitation mode. In this case, the detector may not work correctly. Also, if the electrical cable is buried deep in the plaster, the detector may not make a single sound.

If your homemade detector does not work correctly, you should experiment with a long copper antenna. It can be either shorter or longer than the recommended length. When the detector stops responding to anything except the electrical cable, then you have found the desired length (if you have chosen the wrong length, the detector may respond to a simple touch from a person or any objects).

We have sorted out the nuances, now we move on to the third element of the circuit - this is the piezoelectric element. A piezo emitter (piezoelement) is necessary for auditory perception of the electromagnetic field; when this happens, the emitter makes a crackling sound. A piezoelectric element, or simply a “squeaker,” can be obtained from a non-working Tetris, Tamagotchi or watch. You can also replace the tweeter with a milliammeter from an old tape recorder. The milliammeter will show the level of the emitted field by deflecting the needle. If you decide to use a piezoelectric element and a milliammeter, the crackling noise produced will be a little quieter.

The circuit is powered by a voltage of 9 volts, so we will need a Krona battery. The circuit can be assembled on a printed circuit board or mounted. Wall-mounted installation for a simple circuit consisting of 5 elements would be preferable. Take cardboard, place the microcircuit with the legs down and pierce holes under each leg with a needle (14 pieces, 7 on each side). After preparing the place for the microcircuit, insert the legs into the holes made and bend them. This way we will securely fix the integrated circuit on the cardboard and make the work easier when soldering wires.

To avoid overheating the microcircuit, you should use a low-power soldering iron. Usually a 25 Watt soldering iron is used for soldering radio components. Let's start assembling the detector according to the diagram given in the article. If you have followed all the above recommendations, then the circuit should work instantly without any adjustments. Now we find a suitable case and integrate the circuit into it. Make holes under the tweeter and glue the piezo emitter on the back side. To prevent the detector from working constantly, solder a toggle switch into the power supply circuit break. Rebooting the detector by turning the toggle switch on and off will help you remove the microcircuit from self-excitation mode.

By tradition, I want to end the article with a video report on the work done. The video tested the operation of a homemade and factory-made hidden wiring detector. As it turned out, the made detector more accurately showed the location of the electrical cable than a cheap commercial detector.

Having assembled a detector to search for hidden wiring, you should not be afraid of damage to the electrical network of your home, because you will always be able to find the electrical cable. Good luck in mastering simple circuits in radio electronics. If you have any questions, please contact me in the comments - we’ll sort it out!

About the author:

Greetings, dear readers! My name is Max. I am convinced that almost everything can be done at home with your own hands, I am sure that everyone can do it! In my free time I like to tinker and create something new for myself and my loved ones. You will learn about this and much more in my articles!

Do you want to know if your loved one is cheating on you? Or maybe you're working on a science project?

This simple lie detector can be done at home using fairly simple electronic devices. If you are a child, please ask an adult to help you.

Read also:

1. Find something suitable that you will use as an electrode (conductor). You can use metal alligator clips, but this may cause harm to the person you are testing.

Can be used to make a home lie detector electrode pads for hospital equipment, but requires the use of wire and electrical tape.

2. Assemble the circuit according to the diagram.

Do not attempt to test the device on a person until you have fully assembled it.

3. Attach the electrode to the back of the subject's hand.

Place the electrodes at a distance of approximately 2.5 cm. Place the measuring device where the current strength is zero. If the instrument readings begin to fluctuate, it means the subject is lying.

4. Resistance measurement:

This DIY lie detector is based on measuring skin resistance. When you tell a lie human skin loses part of its ability to resist pressure. Such a system will measure the subject's resistance and alert you when a lie is told. Keep in mind that this system is very simplified compared to professional detectors.

When starting a renovation or just needing to hang a picture, mirror or carpet, the problem arises with finding hidden electrical wiring that can be accidentally touched when driving a nail or screwing in self-tapping screws. Therefore, it is necessary to have a hidden wiring detector that will help you find all the wires in an apartment or private house hidden under the plaster. If you don’t have it, you can do it yourself.

Why are hidden wiring detectors needed?

Very often, owners of apartments or private houses do not have a wiring diagram, which is necessary when carrying out various repairs. While drilling holes or tapping, you may accidentally snag high voltage wires.

Remember! Regardless of whether you know where the electrical wiring is or not, all work must be carried out only when the power is turned off.

If you did the renovations yourself and know where the electrical wires are, this will greatly simplify the work process. But the fact is that wiring is often done by craftsmen who, trying to save money, lay the wires along the simplest path - from the distribution boxes not at right angles as expected, but diagonally. And in this case, you cannot do without a special device that allows you to quickly and accurately find hidden wires - hidden wiring detectors.

Such a detector can be purchased at radio stores or markets. They are inexpensive (budget models) and expensive. The cheap device helps identify live wires and various electrical appliances. More expensive devices are multifunctional and therefore can detect dead wires.

For home use, you can buy the simplest detector or assemble it yourself according to the diagram. Every person who understands electrical circuits can independently make an inexpensive budget device.

Types of modern search devices and their characteristics

Today there are a large number of detectors of various types. Some devices help to find not only wires in the wall, but also accidental breaks.

Based on the principle of their action, the following types of seekers are distinguished:

• Electrostatic.
• Electromagnetic.
• Combined.

Electrostatic testers

Electrostatic detectors help detect electromagnetic fields that come from live wires. These are simple finders that you can make yourself according to a certain pattern.

Features and characteristics of detectors:

• Since the finder responds to certain electromagnetic fields, the wires in the wall must be at high voltage to be detected.
• When working with the device, it is necessary to select a certain sensitivity level, since if it is too low, problems may arise with detecting wires that are too deep in the wall under the plaster. If the level is too high, the device may trigger erroneously.
• If the walls in the room are damp or there are many different metal structures in them, then searching for wiring will be almost impossible.

But given the low cost, ease of use and efficiency, such devices are used even by specialist electricians.

Electrostatic device for finding hidden electrical wiring

Electromagnetic devices

Such devices help to find electromagnetic excitation that comes from wiring connected to a specific load. The quality of work and accuracy of such finders is much higher than previous ones.

Also, these devices have one operating feature. In order to determine where a certain wiring is laid in the wall and how deep, it must have a load of at least 1 kW. For example, you can simply connect an electric kettle or iron to the mains.

Electromagnetic device for finding hidden wiring

Metal detectors (finders)

There are situations when it is impossible to connect voltage to the wires or load, then in this case metal detectors or finders are used. The devices work in this way: various metal elements enter the electromagnetic field of the finder, which cause certain vibrations that are captured by the detector.

Such devices clearly respond to any metal objects located in the walls, so in addition to wires, they will also find them.

Metal detector for finding wires in walls

Combination devices

Detectors of this type are multifunctional, as they are able to combine several types of devices that detect wiring in walls. Such functions significantly expand the range of use of detectors and increase their efficiency.

The TS-75 model, which contains a metal detector and an electrostatic finder, is in great demand.

Combined multifunctional device for finding hidden wiring

Homemade detectors can be:

• With sound indication. During operation of such a device, when it finds hidden wires, a characteristic sound is emitted.
• With sound and light warning system (indication). When the device finds wiring, it not only emits a sound alert, but also the light begins to blink.
• On a field effect transistor. This device is easy to make according to a certain scheme. There are several different options for assembling a device with a warning light.
• Search alarm without batteries. The device operates from the mains, which also signals detection with a bright light located on the finder body.
• Detector on a microcontroller. Such a detector works on the responsiveness of the finder to the electromagnetic field, which is formed by the current flowing through the wires. During assembly, you can use an LED or a piezo sound emitter as a siren.
• Two-element device. The detector has an LED lamp as an indicator, which begins to glow when wiring is detected.

Examples and comparison of popular models

Currently, there are such a large number of different brands and models of devices for searching for hidden or broken wiring that it is difficult to consider everything and describe their characteristics, advantages and disadvantages. Therefore, we will consider only the most popular detectors that are used in home use.

• Electronic tester No. 48M is a multifunctional device for home use, which is used to check the integrity of wires, as well as to locate hidden wiring in the wall using contact and non-contact methods. It has LED indication and can detect wires that are located at a depth of up to 2 cm in the wall.
• The “Sparta” device for searching wiring and metal elements has a sound and light alarm. Allows you to detect not only wires, but also various metal elements. Finds breaks in the circuit.

  Device for finding hidden electrical wiring "Sparta"

• “Search” is used not only to accurately detect wiring in walls and ceilings, but also allows you to check the correct phasing of electric meters, identify equipment with a grounding or grounding break, check the serviceability of fuses, and determine breaks in wiring. Equipped with four sensitivity ranges.

  Hidden wiring detector "Search"

• Finder "Woodpecker M" E121.3 helps to find hidden wiring, check the correct phasing of meters, detect phase wires on various parts of the surface of the room, etc. It has a plastic case with a limiting rib for safe operation and four degrees of sensitivity.

  Hidden wiring detector "Woodpecker M"

• A small non-contact detector UNI-T UT12A made in China allows you to determine voltages from 90 to 1000 V AC. It has a light and sound indicator, as well as an automatic shutdown system after 30 minutes of inactivity. Outwardly similar to a regular marker. Very convenient for home use.

  Hidden wiring detector made in China

• The TS-75 wiring finder in a convenient metal case allows you to accurately determine the location of live wiring in a wall. Has light and sound indication.

  Multifunctional detector for detecting hidden wiring

• The inexpensive American-made S100 STANLEY STHTO-77403 detector is perfect for home and even professional use. Allows you to find not only hidden wiring, but also break points in the circuit. It has small dimensions and a convenient durable plastic case.

  American-made detector "STANLEY"

If we talk about domestically produced detectors, they are perfect for use for domestic purposes. They have affordable prices and can offer good quality. Chinese models are more compact and easy to use. They also have a low cost, but, as we know, this manufacturer cannot boast of a long service life of its products. By choosing brands from well-known European or American manufacturers, you can be sure that the detector will last a long time and will have the necessary amount of functionality for both home use and professional work at an affordable price.

Today, the choice of factory detectors is quite extensive, but some people often get “lost” in such a variety of devices. Therefore, before buying such a device, experts recommend clearly deciding what it is needed for - for single use or for constant work with hidden electrical wiring. Experienced craftsmen usually choose multifunctional devices that can recognize hidden metal elements of various characteristics.

Device for finding hidden electrical wiring for BOSCH brand professionals

When choosing a detector, you need to pay attention to the depth of its scanning. If the device is designed for a shallower depth, then during operation you can pass a wire located at a much greater distance from the wall surface being scanned.

Professional detectors can operate over long distances. Usually, household devices are purchased for home use, which are quite suitable for the walls of apartments, private houses and thin partitions.

Budget options that allow you to find only live wiring are much inferior in efficiency to expensive models, but they will help save a person from burns during work.

Do-it-yourself diagrams for assembling various types of finders

Let's look at the simplest circuits that you can assemble yourself if you have all the necessary devices.

Circuit with audio diode indication

You can make such a device yourself using resistor R1, which protects the circuit from direct induced voltage.

Diagram of devices for locating hidden wiring with light indication

A small copper wire of 5–15 cm is used here as a small antenna. When the device finds wires in the walls or ceiling, a characteristic crackling sound is produced. An audio piezoelectric element is connected to the detector using a bridge circuit that controls the volume level.

Diagram of a device with a light and sound annunciator (indication)

This simple circuit will only require one chip.

Diagram of the detector with light and sound indication

The resistor value of R1 must be equal to 50 MOhm or greater than this figure. An LED light bulb for indication is used without any restrictions on the degree of resistance, since this microcircuit can perform the task assigned to it without “outside help”.

Circuit diagram of a field-effect transistor device

Devices of this type are quite responsive to a stable electric field. This device characteristic is used in the circuit shown below.

Assembly diagram of a device using a field-effect resistor

Such a detector can be made independently without the use of special devices. The voltage indicator should be from 3 to 5 V. To operate this device, so little electric current is required that it can function for about six hours without turning off. The antenna coil is attached using a 0.3–0.5 mm wire to a special Ø 3 mm core. The number of revolutions will depend on the thickness of the wire. If its diameter is Ø 0.3 mm, 20 turns will be required, and if its diameter is 0.5 mm - 50 turns. The antenna works well both with and without the frame.

Metal detector

The metal detector circuit looks like this:

Metal detector circuit diagrams

• Frequency generator VT1 (100 kilohertz).
• Detector - VT2.
• Indication - VT3, VT4.

The generator coils are wound on a special ferrite core. Rod – Ø 8 mm. The number of turns on 1 coil is 120 revolutions, on 2 – 45 revolutions. The recommended wire is PEVTL0.35.

The metal detector is set up away from all steel objects. The adjustment is carried out with special resistors R3 and R5 so that the generation process is significantly reduced (flashing glow of the diode light bulb and low brightness). Then R3 is adjusted to make the emitter go out.

The second step is to adjust the degree of sensitivity. This process is carried out using a small metal object and several resistors. Experts recommend adjusting sensitivity with some regularity. To optimize the process and convenience, regulators are built into the detector body.

The configured metal detector starts working when the antenna is close to metal elements - the light lights up or blinks.

Wiring detector without batteries

This device operates from the electrical network. This circuit operates through the use of a high-capacity capacitor (indicated C1 in the diagram). The capacitor is charged from the mains and in this state can transmit voltage from 6 to 10 V. Here, the brightness of the LED light bulb will depend on the degree of voltage, but this indicator does not affect the operation of the device.

When assembling, you can use an LED or a piezo emitter. When a magnetic field is detected, the indicator starts to work (the light comes on or the emitter starts to crackle).

Such a device can only respond to a certain frequency of 50 Hz. Therefore, errors during operation are excluded here, since it will not respond to other types of frequencies.

Two-element device for finding hidden wiring

It uses a microcircuit and a diode light bulb. You can take a DD1 type microcircuit and an HL1 light bulb. It is necessary to connect the leads so that 3 inverters are created in the electrical circuit. Due to this, the device will amplify the currents supplied to the finder from the magnetic field of the wires. When they are close, the light begins to blink. At a distance it goes out.

Assembly diagram of a two-element detector for finding hidden wiring

Attention! The KP103 transistor can be used of any type, as well as the AL307 light bulb. The whole point is that biopolar poles with such a degree of conductivity have low power, but the transmission coefficient is high. Therefore, instead of the KT203 device, it is necessary to use KT361.

The device is small in size, so it can be assembled even in an empty case from a regular stationery marker. A thin antenna is pulled through a small hole in the felt-tip pen. Its length can vary from 5 to 10 cm. But if the wires are not too deep in the wall (no more than 10 cm), then you can simply use the leg of the selected transistor. This will make it easier and more convenient.

The transistor itself is mounted in a horizontal position, and the gate must be bent so that it is directly above its body.

Video: how to assemble a hidden wiring detector according to the circuit diagram

As many years of experience and practice show, it is not necessary to buy a detector for finding hidden wiring and breaks in a specialized store, since if necessary, you can easily make it yourself, having at least a little experience working with electrical appliances. Such home devices also cope well with their “responsibilities” and find hidden wires.