Homemade devices using motion sensors. DIY laser sensor: design, assembly instructions. Combined motion sensors

Different kinds detectors that allow monitoring of communications and security systems in buildings and private homes make it much easier to manage the entire complex as a whole. Due to built-in algorithms, devices operate autonomously, and human intervention becomes minimal. One of important elements Such circuits are motion sensors. With the help of these devices you can protect the territory from unwanted intrusion and save on electricity. Sensors will automatically turn on and off lighting in the house and on the street, and switch power to other electrical appliances.

Most of these detectors can be made independently; the main thing is to understand the operating principle of these detectors. A DIY motion sensor can be a complex device or, conversely, be assembled from several parts.

Ring switch

To the very simple sensors movements can be attributed to self-return points (ring switches). Such equipment is used when turning on the light in the refrigerator. To operate the circuit, the following is used:

• a reed switch or sealed contact is a flask with 2 ferromagnetic contacts sealed inside it;
• magnet.

When the magnet approaches the reed switch, the contacts close, and when removed, they open. When the contacts are open, voltage is supplied to the lamp in the refrigerator, and the light comes on. When the contacts are closed, the light bulb is de-energized.

Such homemade sensor motion can simply be connected to an existing security alarm or sound detector. Due to this, when the contacts open, that is, the door opens, the system will send sound signal. The scheme is used on the doors of protected objects, but is not suitable for open areas.

To control large areas, more complex devices are used that can respond to various changes in the environment. Such elements include:

• photo, - and sound relays;
• field sensors;
• pyro receivers.

Light motion sensor

Quite often, a motion sensor is needed to detect an object as it moves across a certain line, for example, at the entrance to a room. To create such a sensor, two devices are needed: a light source and a photodetector. When a person passes in the area of ​​the beams, the connection between the source and the receiver will be lost, the sensor will operate and produce a sound signal.

The entire circuit of this device is based on a photocell - a transistor. Moreover, such a phototransistor can also be made with your own hands. To do this, you need to take a transistor that looks like a hat with a brim on three legs, for example, P417A. Needs sawing off top part element so that a hole is formed, or simply open the entire crystal. Now, when exposed to light, the element will begin to work like a phototransistor, although its sensitivity will be slightly less than usual. You don’t have to waste time on this operation, but immediately take a ready-made photocell.

First we assemble the photodetector. The device uses the following elements:

• VT1 – phototransistor;
• R1 – resistor;
• C1 – capacitor;
• DA1 – operational amplifier with feedback;
• R2 – resistor with feedback to the operational amplifier;
• R1 – performs the functions of load and collector. Using this element, the operating point is set. Selection required value goes by experience.

When choosing the characteristics of R2, it should be remembered that the higher the gain, the less stable the amplifier. On the other hand, the higher the resistor value, the greater the gain. It is optimal to use a nominal value of 100 kOhm.

Homemade products work as follows:

• when light hits the transistor, a small operating voltage appears and the element opens;
• the capacitor is charged;
• if the light goes away, the capacitor begins to discharge;
• at point A the voltage decreases, which reduces the voltage at the output;
• An operational amplifier is needed to amplify the signal from point A for further transmission to other devices.

A photodiode can be used as a light source at short distances. The red laser will allow you to significantly gain distance. The laser motion sensor can be used over large areas. But if you need to make the sensor invisible, use an infrared diode.

Attention! When selecting a laser diode, check that its characteristics comply with safety regulations. Some of these elements have a detrimental effect on the eyes.

The photosensor itself must be darkened and covered with dark transmissive material. This will reduce the influence of conventional lighting. We place the light source opposite the sensor. Due to this, it is formed optical communication, that is, until the object covers the light source (crosses the line), the voltage in the phototransistor will be constant. When the optical connection is broken, the output voltage is reduced to zero by the operational amplifier.

To analyze the data coming from the sensor, a relay should be connected to the circuit. We connect the winding to the input, apply 12 V to 1 contact, ground the other end, and connect the third to the radio. If light falls on the photocell, the power circuit is connected to the photodetector, the radio does not work. If the optical link is broken, the voltage drops and the power supply is shorted to the radio. This causes the radio to turn on. Instead of a radio receiver, other detectors can be used.

Motion sensors with capacitive relay

The capacitive relay reacts to the occurrence of objects within a given radius. The main elements of such equipment are an antenna and a microwave generator.

Many of us have noticed that the sound of a radio changes when a person gets very close to it, strange noises appear in operation, or the station’s waveform gets lost. They function on exactly the same principle microwave sensors movements.

The role of the high-frequency generator of the radio receiver in the circuit is simultaneously performed by transistor VT1. A detector diode is needed to rectify the voltage, which sets the bias at the base of transistor VT2. Transformer T1 has windings tuned to different frequencies. If the antenna is not affected by external objects, there is no voltage on the VD1 detector, since the signal amplitudes cancel each other. If the frequencies change, the amplitudes begin to add up and are detected on the diode. Due to this, VT2 opens. In order to accurately set the value for turning off and turning on, a comparator is used - thyristor VS1. This thyristor is controlled by a 12-volt power relay.

Important! Sensors should not be placed near fans or large household appliances. All this equipment can interfere with the operating mode of any sensor.

Design Platforms

To create more complex and functional devices, you can use ready-made boards for radio design, for example, Arduino. This is the name of a hardware computing platform with its own processor and memory. Arduino performs several important tasks at once:

• reads and processes the signal from infrared sensor;
• reacts to movement;
• carries out notification.

To create the sensor you will need the platform itself, a PIR sensor, a breadboard and wires. You can connect the sensor directly to the Arduino, but it is more difficult to ensure a tight fit. Therefore, it is more convenient to use a Bradboard.

All infrared sensors have the same structure. The main parameter by which one sensor can be distinguished from another is sensitivity, and, therefore, the optics used. The optimal PIR sensor today is a device with Fresnel lenses. These lenses can concentrate radiation, increasing the threshold of sensitivity.

The main task of the platform is to send data via USB Serial when motion is detected at certain intervals. Debugging of equipment is carried out due to software Python and PySerial.

Such a motion sensor for turning on the light can be programmed to create a certain level of illumination. This equipment can be used to set up an alarm system in the garage, then the detector will be connected to the sound module.

Video

A motion sensor is most often used to turn on lights when you pass or are near them. With its help, you can save electricity and save yourself from having to flip the switch. This device is also used in alarm systems to detect unwanted intrusions. In addition, they can also be found on production lines, they are needed there for the automated execution of any technological tasks. Motion sensors are sometimes called presence sensors.

Types of motion sensors

Motion sensors are distinguished by their operating principle; their operation, accuracy and features of use depend on this. Each of them has strengths and weak sides. The final price of such a sensor also depends on the design and type of element used.

The motion sensor can be made in one housing or in different housings (the control unit is separate from the sensor).

Contact

The simplest motion sensor option is to use or. Reed switch (sealed contact) is a switch that is activated when magnetic field. The essence of the work is to install a limit switch with normally open contacts or a reed switch on the door, when you open it and enter the room, the contacts will close, turn on the relay, and it will turn on the lighting. Such a diagram is shown below.

Infrared

They are triggered by thermal radiation and react to temperature changes. When you enter the field of view of such a sensor, it is triggered by thermal radiation from your body. The disadvantage of this detection method is false positives. Thermal radiation is inherent in everything that is around. Here are some examples:

1. stands in a room with an electric heater, which periodically turns on and off according to a timer or thermostat. When the heater is turned on, false alarms may occur. You can try to avoid this by taking a long time and carefully adjusting the sensitivity, as well as by trying to direct it so that there is no heater in the direct line of sight.

2. When installed outdoors, it may be triggered by gusts of warm wind.

In general, these sensors work normally, and this is the most cheap option. A PIR sensor is used as a sensitive element, it creates electric field proportional to thermal radiation.

But the sensor itself does not have a wide directionality; a Fresnel lens is installed on top of it.

It would be more correct to say - a multi-segment lens, or a multilens. Pay attention to the window of such a sensor, it is divided into sections; these are lens segments; they focus the incoming radiation into a narrow beam and direct it to the sensitive area of ​​the sensor. As a result, radiation beams from different directions fall on the small receiving window of the pyroelectric sensor.

To increase the efficiency of motion detection, dual or quad sensors or several separate ones can be installed. Thus, the field of view of the device expands.

Based on the above, it should also be noted that the sensor should not be exposed to light from the lamp, and there should be no incandescent lamps in its field of view, this is also a strong source of IR radiation, then the operation of the system as a whole will be unstable and unexpected. IR rays don't travel well through glass, so it won't work if you're walking behind a window or glass door.

This is the most common type of sensor; you can buy it or you can assemble it yourself, so let’s look at its design in detail.

How to assemble an IR motion sensor with your own hands?

The most common option is the HC-SR501. It can be bought at a radio parts store, on Aliexpress, and is often supplied in Arduino kits. Can be used in conjunction with a microcontroller or independently. He is printed circuit board with a microcircuit, harness and one PIR sensor. The latter is covered with a lens, there are two potentiometers on the board, one of them regulates the sensitivity, and the second is the time at which a signal is present at the output of the sensor. When motion is detected, a signal appears at the output and lasts for the set time.

It is powered by a voltage of 5 to 20 volts, operates at a distance of 3 to 7 meters, and the output signal lasts from 5 to 300 seconds, you can extend this period if you use a microcontroller or a time delay relay. The viewing angle is about 120 degrees.

The photo shows the sensor assembly (left), the lens (bottom right), and the reverse side of the board (top right).

Let's take a closer look at the board. There is a sensitive element on its front side. On the back there is a microcircuit, its wiring, on the right there are two trimming resistors, where the top one is the signal delay time, and the bottom one is the sensitivity. In the lower right part there is a jumper for switching between modes H and L. In mode L, the sensor produces an output signal only for the period of time set by the potentiometer. Mode H produces a signal while you are in the range of the sensor, and when you leave it, the signal will disappear after a time set by the upper potentiometer.

If you want to use a sensor without microcontrollers, then assemble this circuit, all elements are labeled. The circuit is powered through a quenching capacitor, the supply voltage is limited at 12V using a zener diode. When a positive signal appears at the sensor output, relay P is turned on through an NPN transistor (for example BC547, mje13001-9, KT815, KT817 and others). You can use a car relay or any other with a 12V coil.

If you need to implement some other functions, you can use it in conjunction with a microcontroller, for example. Below is the connection diagram and program code.

Ultrasonic

The emitter operates at high frequencies - from 20 kHz to 60 kHz. This leads to one problem - animals, such as dogs, are sensitive to these frequencies, moreover, they are used to scare them away and train them. Such sensors can irritate them and this causes problems.

The ultrasonic motion sensor operates on the Doppler effect. The emitted wave, reflected from a moving object, returns and is received by the receiver, while the wavelength (frequency) changes slightly. This is detected and the sensor produces a signal that is used to control a relay or triac and switch the load.

The sensor processes movements well, but if the movements are very slow, it may not work. The advantage is that they are not sensitive to changes in conditions environment.

Laser or photo sensors

They have an emitter (for example, an IR LED) and a receiver (a photodiode of a similar spectrum). This is a simple sensor, it can be implemented in two versions:

1. The emitter and photodiode are mounted in the passage (controlled area) opposite each other. When you pass through it, you block the radiation and it does not reach the receiver, then the sensor is triggered and the relay is turned on. This can also be used in alarm systems.

2. The emitter and the photodiode are located next to each other, when you are in the range of the sensor, the radiation is reflected from you and hits the photodiode. This is also called an obstacle sensor and is successfully used in robotics.

Microwave

It also consists of a transmitter and receiver. The first generates a high-frequency signal, the second receives them. When you pass nearby, the frequency changes. The receiver is configured in such a way that when the frequency changes, the signal is amplified and transmitted to an actuator, such as a relay, and the load is turned on.

Microwave motion sensors are very sensitive, allowing you to “see” an object even behind a door or behind glass, but this also causes problems of false alarms when the object is outside the field of intended visibility.

These are quite expensive sensors, but they respond to even the smallest movements.

Capacitive devices work in a similar way. Such a diagram is shown below.

How to connect a motion sensor?

You can come up with countless options and schemes for connecting a motion sensor depending on your needs; sometimes you need the system to be triggered when you move in different places, For example street lighting along the way from the house to the gate and vice versa, in other cases it is necessary to force the lights on or off, etc. We will look at several options.

Typically a motion sensor has three wires or three terminals to connect to:

1. Coming phase.

2. Phase leaving to power the load.

If you do not have enough sensor power, use an intermediate relay and. To do this, instead of a light bulb in the circuits below, the coil terminals are connected.

The photo below shows the terminals to which the power wires are connected.

Conclusion

Using motion sensors is, as much as it sounds, a step. Firstly, it will help save energy and lamp life. Secondly, it will eliminate the need to flip the switch every time. For outdoor lighting correct settings You can make the light turn on when you approach the gate of the house.

If the distance from the gate to the house is 7-10, you can get by with one sensor, then you won’t have to lay a cable to the second sensor or assemble a circuit with a pass-through switch.

As already mentioned, IR sensors are the most common; they are sufficient for simple tasks; if you need greater sensitivity or accuracy, take a closer look at other types of sensors.

Or you can simply make the light in the entrance of the house turn on only when someone is in it, you can make a motion sensor. Despite the fact that this seems complicated, within the framework of this article you will be able to see for yourself: it is not so. You may be interested in making a motion sensor for your lighting. Can also be implemented burglar alarm- everything depends on your imagination.

Let's say a word about sensors

First, the easiest and most primitive schemes will go, and in the end you will see much more complicated and more interesting solutions. But first, a little preface. If you want to get acquainted with how infrared sensors work, or you think you will see circuits here that will be difficult to assemble at home, you will be disappointed. This article is completely and entirely aimed exclusively at those who broaden their horizons, want to understand the principle of operation and assemble a few simple circuits in order to get their hands on creating similar devices and understand how to make a motion sensor with their own hands.

The simplest and… non-working option

So, the simplest option that radio amateurs could come up with is to create a motion sensor that will be built on a wirewound resistor (also known as a potentiometric resistive converter). For greater accuracy, it should be clarified that this sensor is focused not so much on movement as on movement. But its simplicity makes it worthy of attention. Let's say you want to detect how some small object moves linearly from one point to another. A displacement sensor will also work for this. Here is its main purpose, which is well illustrated in the image. As you have already seen, nothing complicated. Some object is connected to the motor, and it, in turn, moves along the resistor. At the same time, the voltage of the voltmeter changes. But the design, alas, is not entirely working. Its problem is that linear movement is not converted into fault-free voltages due to the fact that the sensors are connected to some kind of load (in this case a voltmeter).

The simplest working option

This DIY motion sensor can already be used to achieve motion control goals. But the price of this was a certain complexity of the provided scheme. Well, we suggest you pay attention to the diagram, familiarize yourself very carefully with its structure, and then study what is needed for:

1. GB1 - this is how the power source is designated;
2. V - a voltmeter is connected here;
3. R1 is a wirewound resistor, which is the most important such device in the circuit;
4. R2 is a resistor that is necessary to bypass the upper arm of the potentiometer.
5. R3 - load resistance. You can connect any type of indication, from ordinary light bulbs to circuits that reproduce sound.

Now look at the graph and remember the resistor from point #4. The lines represent the conversion of object motion into tension. Red - in cases where there is no R2, and green - if there is one. The advantages can be said that it is easy to assemble and is quite accurate. There is only one drawback - a little debugging is required before using the device.

Motion sensor with photocell

Here you will face a more difficult task, and at the same time interesting job. First you need to get a photocell (a phototransistor is best). It can be made by hand due to its simplicity of design or purchased in a store. As part of the article, we will talk about MP41. First, saw off the top part of its body so that the crystal is exposed. When light hits it, it will work as a photocell, although with relatively low sensitivity. But, nevertheless, this is a full-fledged motion sensor, assembled with your own hands.

Scheme

For a sensor with a photocell to work fully, it is necessary to assemble a photodetector circuit. To influence the switch/switch, a photo relay is added - and the design is ready. As you can see, it is not difficult to make a motion sensor with your own hands. In addition, experience and practice will allow you to gain experience and in the future assemble devices that can be very useful at home, with the prospect of their successful commercial implementation.

On given time The most common and popular motion detection device is volumetric, passive, .

The principle of its operation is based on the reception of thermal radiation from any object by a pyroelectric infrared receiver. This element works in conjunction with a field-effect transistor, which acts as a pre-amplifier.

In order for the range of thermal waves emitted by the human body (5 - 14 microns) to be perceived by the photodetector, special light filters are used

To minimize false alarms, the sensor design includes two such receivers connected in a counter circuit.

Depending on external illumination and temperature, voltages are generated by each sensor separately. Their signals are subtracted and compensated, and when the threshold value is exceeded, the device reacts to movement.

Motion sensor LX01

Let's take the LX01 detector as an example. The device consists of two boxes: mounting and hardware, which are connected by a movable bracket that facilitates setting the scanning area.

The hardware box contains a control board to which sensors are attached: a pyroelectric one that recognizes movement, a photosensitive photoresistor for determining the level of illumination.

The sensors are covered by a translucent plastic curtain with Fresnel lens elements pressed out over the entire area.

At the end there are corrugated handles for operational regulators connected to trimming resistors.

The mounting box has holes for wiring and mounting the housing. lighting fixture.

The device is intended for switching electrical circuits With total load up to 1200 W. The device can be connected to incandescent lamps and other lighting elements designed for an alternating current voltage of 200 - 230 V.

Unlike detectors used exclusively for Extra options regulating operation.

“TIME” regulator – adjusts the time after which the device turns off the lighting; if a person continues to be in the range of the device, the light will be turned on again.

Unlike presence detectors, motion sensors, when switched again, completely turn the lighting device on and off at a fast pace, which, if the response period is incorrectly set, leads to flickering of the light.

“DAYLIGHT” regulator – sets the light sensitivity of the device and allows you to accurately determine the eclipse threshold for automatically turning on the lighting.

“SENS” regulator – sets the sensitivity of the pyroelectric sensor of the detection detector. It can be used to adjust the radius of the detection zone.

• The scanning zone angle is 120 0 .
• Maximum detection range 12m.
• Power supply: alternating current from 180 to 240V at 20mA.
• Shutdown time 5sec-600sec.
• Photosensitivity in the range of 10-2000 Lux.

The device is sensitive to low temperatures environment and maintains performance only down to -10 0 C. Installation in rooms at a height of 2 m to 4 m is recommended.

Schematic diagram of a motion sensor

The LX01 model includes an infrared sensor that detects movement and elements that amplify and process the signal.

A passive, infrared pyroelectric sensor is a transparent quartz plate that transmits infrared rays and a ceramic sensor.

There is also an amplifier in the housing that matches the high output voltage coming from the sensor.

The RE-46 pyroelectric sensor, which is used in the LX01 motion detector, is connected to an LM324N operational amplifier. He has complex structure, consisting of four stages of amplifiers.

The functions of amplifiers DA1.1 and DA1.2 are to correct the incoming signal and then transmit it to the third stage - DA1.3.

The comparator, which is connected to it, recognizes the preprocessed signal. The fourth stage DA1.4 regulates the lighting time.

It should be noted that with this principle of processing incoming signals, the determination of a moving object is reduced not to, but to the identification of dynamic changes in such radiation.

The photoresistor (R23), which determines the level of external lighting, is controlled by the tuning resistor R24, which in turn is connected to the base contact of the VT1 transistor.

If the light intensity increases, then the resistance of the photoresistor drops, and accordingly the current at the base of the transistor increases. It opens and the effect of raising the contact potential between resistors R25 / 21 and the ground potential occurs.

Thus, the signal from the DD1.4 cascade is prohibited from entering the base terminal of transistor VT2, which activates the connecting relay K1. If the relay is triggered earlier, the operation of the photoresistor will be blocked by diode VD4 for the entire period of the active phase.

The device operates from a regular power supply 220V, 50Hz. Voltage is supplied to the device through the fuse FU. Through the input of the quenching capacitor (C11 in the diagram) and the diode bridge (VD7-10), the output voltage will be 18 - 22 volts.

Next, the voltage is smoothed and rectified by capacitor C12 and supplied to the DA2 78L08 stabilizer. The increased voltage that appears at the output of the stabilizer is sent to the zener diode (in the VD6 diagram), which dampens it to 24V. When switching relay contacts, switching noise occurs, which is suppressed by a sequence of resistor R26 and C10.

Connection diagrams

This model is designed for direct connection of lighting devices powered from the mains with alternating current 220V, but the power of connected devices is limited to no more than 1 kW.

Which provides for both automatic and manual switching on of the lighting device, the following diagram for connecting the motion sensor through a junction box is used.

It is possible to connect several. Such circuits are used to refresh staircases or long corridors that cannot be fully monitored by a single detector.

In order to increase the maximum load, use the method of connecting a motion sensor through an intermediate relay.

In this case maximum power consumption will be limited only by the parameters of the load capacity of the intermediate relay used. Thus, it is possible to connect powerful halogen spotlights with a load of several kilowatts.

Using as lighting elements, mercury lamps daylight, it should be remembered that the period between switching on must correspond to the cooling time of the lamp.

Rules for installing a motion sensor

On the stability and efficiency of the system alarm system The location chosen to install the motion detector is affected.

In this case, it is necessary to choose correctly not only general scheme, but also a connection point in each room. When determining it, it is necessary to minimize Negative influence external factors, which can lead to false alarm alarm systems.

Avoid exposure to convective or intense heat in the trigger area. air flow(air conditioners and radiators), as well as direct sunlight.

In addition, the surface on which the sensor is installed should not be subject to vibration or vibration (from opening a door or window).

The traditional installation of the detector is in a shaded corner of the room at a height of no more than 2.4-3 m with the scanning area directed towards the center of the room.

Symbols on the diagram:
1. Motion sensor
2. Glass break sensor
3. Reed switch
4. Smoke detector

A fairly common practice is sound and motion sensors in the house. We suggest you consider how to make motion sensors with your own hands, instructions, diagrams and photos in our article.

How the device works

The operation of the device is based on the reception and transmission of impulses emanating from the vibration of air (or water, for example, in swimming pools) while moving (and it does not matter whether it is a car, a person or an animal). The functionality of the device may vary depending on the requirements for it. There are several types of motion sensors:

• thermal (react to temperature changes in the reachable field). Most shining example– infrared or laser sensor, mainly used in security systems;
• sound (transmit and receive impulse when air vibrates from sounds). A very simple device, used to record movement in open space;
• oscillatory (respond to environmental fluctuations and changes in the magnetic field when moving within reach). They are most often used in an apartment or house to turn on or off lights, sound, and other things.

How to make a sensor

Let's look at how the most common motion sensor for alarm is created. It is done based on this scheme

You need to prepare the following tools and parts:

• voluminous body (can be taken from an old camera);
• Soviet-style control element base (buy at any store electrical goods or at a flea market);
• soldering machine;
• wires;
• screws;
• screwdriver;

Step by step guide

An autodyne is assembled on the basis of a transistor, which has now become a local oscillator and a mixing device for signaling. As soon as air vibrations (movement) are detected in the field protected by the device, the signal level will change. It fully corresponds to the Doppler shift, and will be equal to several hertz.

Video: how to make a motion sensor with your own hands

Next, with the help of a capacitor (in the diagram C2) and a low-pass filter (shown as C1, L3, the pulse will be sent to the alarm contact, which will also be a filtering part. Thanks to this, the pulse will reach its maximum and maintain these parameters for a certain time. Resistor (on Figure R11) will adjust the sensitivity of the circuit.

The comparators in this case are VD3 - a zener diode and a small relay (K1). It is imperative to take into account that the nominal mains voltage is 11 volts. Because of this, we also recommend connecting a signal-boosting stabilizer to the circuit.

Step two: adjust the board to the required parameters

There is an antenna at the top of our board; it needs to be thoroughly polished and treated with degreasing solutions; it is very advisable to cover it with rosin or at least acetone, because there is a high probability of oxidation of the antenna material during its use.

Next you need to wrap coil L1 and coil L2 with twelve turns of small-section wire (we took PEL-0.23).

Using a screw with a diameter of 3, screw the bushing to the central hole of the future sensor, secure it, and check the strength of the connection.

Now let's start fitting our body. We measure it, we need the board to fit into the box freely, i.e. the body is either sawn or another one is selected. In it we mark the location of the center of the board and there we also drill a similar hole, as in the diagram, treat it with acetone, and try on the board.

Three millimeters need to be drilled into the corners of the housing where installation is taking place. electrical diagram. Some deviation is allowed depending on your mounting screws.

The screws, sleeve and plates can be of any material, but be sure to check that the holes and legs are even. In some cases, you will still need to drill holes for future LEDs, but basically they are visible through the body.

The simplest sensor is ready, when assembled it will look something like this. The installation is carried out according to a clear scheme: we connect a room lamp or a fluorescent lamp to the detector.

How to make a laser motion sensor

In the movies, everyone has seen lasers that signal the entry of robbers into a bank. Making an electronic motion sensor with your own hands using a laser is also not as difficult as it seems. You need to prepare the following components:

• infrared diode or photodiode, depending on capabilities and requirements;
• capacitive relay type RES55A,
• wire diagram;
• transistor and resistor blocks;
• Charger at 5 volts;
• multimeter;
• other tools and parts (gasket, screws, soldering iron).

First, let's disassemble the charger. We expose the wires and find positive and negative contacts there. Next, according to the rules, we need to set our resistor to minus. Now we connect a diode to it using a cathode, and the anode must be soldered to the adjustment resistor. Next, we solder the transistor emitter to the negative wire and connect a resistor to the base circuit.

In total, we get: resistor - minus, contactor - to the relay, relay - signaling device. The schematic diagram of an infrared sensor looks something like this:

Using a screw, you need to attach this entire structure to the gasket, and connect the power wire to the screw head. Important: install the connecting screw so that it rests against the spacer spring; in this circuit it is a sensitive part.

This light alarm can be installed anywhere as long as there is an outlet nearby. It is most logical to place it at foot level.

Any of the above options can be customized to suit individual needs.

1. The webcam itself can act as a motion indicator. If you connect it to the alarm, it will even make sounds, but in most cases it is enough to just download a special program to your computer;
2. When connecting the sensor to the lighting system, make sure that there are no fans or large household appliances within its reach;
3. To create with your own hands " smart home» We recommend using a touch switch. The fact is that in most cases there is already a built-in motion sensor;
4. Select diodes for your laser carefully. IR radiation can be harmful to the eyes, so it is not recommended for domestic use;
5. Car alarms are made using a similar principle. Only to schematic diagram an audible alarm is also attached. When the sensor detects movement, a light comes on and a tone sounds, similar to a metal detector. Such a device is also called a radar sensor;
6. If desired, include a capacitive display in the circuit; it will display the “Work” and “Stop” indicators. Or connect the monitor to a circuit similar to a webcam, and get a full-fledged home video surveillance network;
7. It is quite possible to make a GSM alarm on a regular phone; to do this, you just need to download the program, just like on a PC.

If you need to carry out repairs, then all the indicators can be disassembled very quickly and basically the problem lies in the contacts, just clean them.

When you simply don’t have time to make motion sensors yourself, you can buy them at any electrical store, good feedback about GrandWay and Siemens models. The average price of the device is 500 rubles.