Motion sensor diagrams: types, device, connection and principle of operation

Using special devices, you can control unauthorized entry into a protected area. In addition to security systems, appropriate tools are used to automate individual work processes. You can create your own motion sensor using the instructions given in this publication.

Laser alarm will prevent theft of valuables from your home safe

How the device works

Any alarm operates on the principle of monitoring a certain perimeter. Special sensors record movements. The alarm signal is transmitted to the security console. A duplicate message is sent to the owner of the apartment or other property. Using the GSM unit, a secure communication channel is provided. By connecting the battery, they maintain operability in case of accidents (intentional disconnection) of the standard power supply.

For your information. Specialized systems are complemented by fire alarms. In this option, the duty officer of the Ministry of Emergency Situations receives an additional notification.

A similar design solution, but without a message to the user and duty services, is used to automate regular operations. A typical example is lighting a dark vestibule. The installed homemade product will turn on the light only when necessary. The cost of parts is much less than the cost of saved electricity. Don't forget about additional amenities. A similar sensor can be used to automatically open gates when a car leaves the territory of a personal plot of land.

Complex application

The best method of increasing the sensitivity of thermal motion detectors is to use them in combination with similar ones, but operating on different physical principles:

  • Trapping optical waves (change in lighting).
  • Sound - while moving, all objects produce air vibrations audible to the ear.
  • Echolocating is when equipment creates a directed wave pulse (invisible to human eyes) and receives the signal reflected from objects to sensors. Based on its change, a conclusion is drawn about the movements of something in the controlled field.

Each of the detectors listed has pros and cons depending on their detection methods. But, working together, they create for the overall system an almost complete range of feelings for determining movements in the sensory field. Roughly speaking, they can see, hear and sense human movements.

Types of sensors

kVA to kW - how to correctly convert power

The designs presented below should be considered taking into account a certain technical specification. In a closed heated room, the electronic module can stand for a long time without damage. Outdoors you will need protection from adverse natural influences. In some situations, it is necessary to provide effective anti-vandal measures. With a significant size of the protected perimeter, range becomes essential.

For your information. On the land plot, it is necessary to exclude false alarms from the movement of domestic animals and birds.

Contact or magnetic

Without detailed explanations, the operating principle of a simple device with mechanical contacts is clear. The button (without a lock) is installed on the frame of the door block. When opened, the connected circuit is closed, the signal is sent to a control lamp or a special remote warning unit. In addition to minimal costs, such a device is attractive due to the speed of implementation of plans. For objectivity, you need to list the existing shortcomings:

  • the door frame is damaged during installation;
  • the functionality of the security system is blocked by pressing a button (with a knife blade, bank card);
  • A mechanical switch will quickly become damaged if used frequently.

Contact sensor and circuit with reed switch

Instead of the simplest option, you can use an improved circuit with a reed switch. This part completes the circuit when the magnet is removed. In addition to the best aesthetic parameters, the possibility of hidden installation is provided. You should pay attention to the autonomy of the device and the lack of power consumption in standby mode.

IR sensor

The considered options provide control of the door block. However, they are useless in open space. To fix movements within a certain volume, other solutions are used.

An intuitively understandable principle is the registration of thermal radiation from the human body. To amplify the signal, a group of several lenses is used. The same device provides a wide radiation pattern. Select a sensor corresponding to a certain wave range. Sensitivity and spectrum are corrected with filters and additional amplifiers.

Such devices perform their functions well in the absence of unnecessary interference. IR sensors are installed indoors and are not directed at lighting and heating devices when installed. The basic condition is that the background temperature must be less than the measured parameters.

Laser or photosensor

Devices in this category create beams that form a protective circuit. To create a sufficiently dense “grid”, a powerful light source and a set of reflectors are used. The best option is a laser motion sensor. Such a beam does not scatter over a long distance. An interruption of the signal is detected by a sensitive sensor. Large objects and open areas are equipped with such systems.


The main advantage of this design is high-quality control of movements within a certain volume. An additional plus is the absence of false alarms when lights or heaters are turned on. To implement the plan, it is necessary to create an emitter and a compatible detector that detects changes in the reflected signal. When working at high frequencies, movements are detected behind glass or other obstacles that are “transparent” to waves in the corresponding range.

Important! When choosing such a device, the power is adjusted taking into account the level of electromagnetic radiation that is safe for humans.

Operating principle of a microwave motion sensor


As in the example with light, this circuit operates on the principle of recording reflected radiation. The audio range provides “invisibility”. The ultrasonic generator consumes little electricity. The sensor does not respond to light and heat.

For your information. Some pets react to high-frequency sound vibrations. This range is used in specialized dog repellent devices.

Homemade on Arduino

To create workable designs, it is convenient to use the universal Arduino controller. Connecting peripheral devices to this functional block is easy.

Step-by-step instructions for creating it yourself

In order to create a motion sensor yourself, you need to have soldering skills and know the basics of radio engineering or electrical engineering. The diagram of such a device is posted on the Internet, freely available, and finding it will not be difficult.

Before you get started, you should purchase the following items:

  1. A small plastic box (approximate dimensions: length - 8 cm, height - 5 cm, width - 5 cm), the housings of old cameras, alarm clocks, and music speakers are well suited for this.
  2. Power supply with an output voltage of 5 volts (phone charger is suitable).
  3. Transistor , any photocell, relay and tuning resistor with a resistance of 10 kOhm (these elements can be purchased in specialized stores of radio elements, on radio markets or ordered on the Internet).
  4. Soldering machine with a thin tip , power 40 watts, soldering acid and tin.
  5. Several meters of wires of various sections (0.3 mm2, 0.5 mm2 and a small piece of 1.5 mm2), which should be purchased only from reliable manufacturers, since Chinese products do not always correspond to reality.
  6. Short self-tapping screws , 15 mm long.
  7. Screwdriver with a shaped tip.

Step-by-step instruction:

  1. Step 1. Assembly begins with mounting the board. To do this, you need to transfer the diagram from paper to a suitable piece of plastic. In order not to make a mistake with the dimensions, fit this piece to the plastic box in advance, and then proceed with mounting the board. Installation occurs in the following sequence:
      Solder the cathode of the photocell to the positive pole of the charger, and solder a trimmer resistance to the anode.
  2. Attach a resistor to the board, connect one of its ends to the negative pole of the charger by soldering, and solder the other to the base of the transistor.
  3. Place a relay in the circuit, solder its free end to the negative pole of the power supply, and connect the free contacts to the load.
  4. If higher power is required, an additional relay is installed instead of the load.
  5. Connect the laser flashlight to the charger permanently and install a self-reset switch in the open circuit. Do not forget about the soldering points, because they have the highest probability of burning out; it is best to use soldering acid
  6. Step 2. Fill the elements of the mounted board with special radio-technical glue, paying special attention to the connections.
  7. Step 3. Place the processed board in a pre-prepared plastic case and secure it in 4 places (in the corners) with self-tapping screws. Close the case, for reliability you can put it on glue.

The infrared motion sensor is ready, its basis is a relay. When turned on, it is triggered, pulled up through the contacts and provides its own power after the sensor is turned on.

Circuits for homemade motion sensors

Cable ties

The options presented should be considered based on personal experience. PCB etching and other complex technologies should be mastered in advance. Too high a temperature and other installation errors can damage microcircuits and radio components.


This circuit presents a generator (100 Hz) assembled on a field-effect transistor VT1. The circuit of the induction coil (L2) and the capacitor (C2) is adjusted accordingly (to the resonant frequency). Detector – diode VD1.

Capacitive sensor

Resistor R3 in this circuit sets the reference voltage. If you move closer to the sensor (A), the capacitance and initial setting of the generator will change. Reducing the frequency will disrupt the operation of the resonant circuit and reduce the amplitude of the signal at the transistor input. To connect peripheral devices, you can use a switch of the required power (thyristor VS1).

Thermal sensor on Arduino

To assemble this circuit, you need to prepare the following functional components:

  • IR range sensor;
  • serial Arduino controller;
  • power supply 5±1V.


When starting to develop an alarm project using motion sensors using old Soviet elements, it is recommended to find old Soviet magazines for radio amateurs or designers.

The country has many defense design bureaus and masses of radio enthusiasts. In magazines for DIYers, such circuits were often described using simple radio components, in many ways, which were developed by real professionals.

It would be a good idea to use ready-made sensors as sensors with the ability to connect both lighting and sound devices.

How to make a laser motion sensor

This circuit can be created using an inexpensive laser “pointer”. The photosensitive sensor is connected to the control terminal of the thyristor. A powerful load can be connected through a relay in the circuit. This example shows the possibility of transmitting an alarm signal to the user using GSM mobile communication lines.

Laser alarm with remote notification

Security alarm from a ready-made kit

The simplest security device based on an autonomous alarm system can operate wirelessly. In stores for radio amateurs you can find two options - based on an infrared sensor (aka motion) or a magnetic contact sensor that reacts to opening. True, the choice is not large enough and you will often have to go shopping to find the product “in stock”. Therefore, the easiest way to purchase this product is to order it in one of the large online stores.

Kit based on an infrared sensor.

An example is the Chinese alarm system under the loud name “Alarm mini”. Consists of the IR sensor itself, a mounting bracket and one or two key fobs. The kit includes clear instructions for installation and operation. 4 AA batteries are purchased separately, but can also be powered by a 6V power adapter (sold separately). Installing it yourself is not difficult.

After inserting the batteries into the device, you need to install the unit itself in such a place that its lens is directed towards the protected area. The front panel has an infrared receiver window for controlling the alarm from remote controls. A lens that “detects movement” in the controlled area, operation lights and a siren.

We press the button on the remote control - the green LED lights up, which means the exit report has started (15-20 seconds), so that we have time to leave the apartment. Then the green eye goes out - the device has started working. Now, as soon as there is any movement in the room, a person will pass, a dog or cat will run, the red LED will light up and after 15-20 seconds a very loud siren sound will be heard. The device works!

The price of the device is about 500 rubles and depends on the current dollar exchange rate and the place of purchase. You can find various options, for example, here


A set based on a magnetic contact sensor.

A security alarm based on an opening sensor is a main unit that contains a sensor with open contacts and a magnet for closing these contacts.
You need to set them up against each other so that there is direct contact between them. If a thief breaks into the house, when a door or window is opened, these elements move away from each other and an alarm siren sounds. Such an alarm can be used mainly to scare off intruders and its main advantage is its low price, about 100 rubles per sensor. And very simple installation, there is adhesive tape on each part, just remove the protective layer and stick the sensor on the front door or window.

Often such kits are used to protect the perimeter of the house while you are inside, for example, sleeping at night. The sound of the siren will wake you up and you can take any action to protect yourself.

Connecting the device and setting sensitivity

As an example, you can use the algorithm of actions when choosing a typical pyroelectric module HC-SR501. The first variable resistor adjusts the sensitivity. In addition to the distance (up to 7 m), this parameter can limit the size of detected objects. The second regulator sets the required time to delay the control output pulse. The jumper position sets the mode:

  • H (default) – time countdown starts from the moment motion is detected;
  • L – motion detection resets the timer.

Setting items



In the modern market of electrical products, prices vary depending on the assembly, the quality of the electronic component of the product and the manufacturer's warranty.

The IEK company produces high-quality and inexpensive products. Prices for motion sensors start at 499 rubles. Both wall and ceiling models are produced with different grip angles. Almost all devices have a degree of protection of IP 44, which allows the company’s products to be used under adverse conditions. Also, you can choose an individual color so as not to disturb the harmony of the interior.

REV RITTER produces motion sensors with a stylish design, which allows them to be installed in inconspicuous places, for example when creating a home alarm system. The average price for campaign products is 750 rubles.

BRENIN is the most popular, as it has a golden ratio of quality and price. The company's products are 80% wireless and have such criteria as the installation location (street or home), and are mainly tailored for the Smart Home system.

There is a very wide variety of colors, shades and designs, which allows customers to choose the most suitable option for themselves. BRENIN sensors have several operating modes; they can be turned on during the day, at dusk and at night. The device can be mounted on absolutely any surface.

The cost of electrical products from the BRENIN campaign starts from 1,500 rubles.

( 1 rating, average 4 out of 5 )
Did you like the article? Share with friends:
For any suggestions regarding the site: [email protected]
Для любых предложений по сайту: [email protected]