PIR sensor: description and connection instructions

In rare cases, modern alarm systems do without touch components. It is sensitive sensors that make it possible to detect anxiety signs for various indicators. In house security systems, such tasks are performed by light detectors, impact sensors, leak detection devices, etc. But if we are talking about the security function, then the PIR-motion sensor, working on the principle of infrared radiation, comes first. This is a miniature device that can itself act as an indicator of the state of the serviced site or enter the general security complex. As a rule, the second variant of using the sensor is chosen as the most effective solution.

General information about the sensor

Almost all motion sensors are designed to detect strangers in the room. The classical security system assumes that the sensor will record the fact of intrusion into the controlled area, after which the signal will go to the control point and then some measures will be taken. Most often, a signal is sent in the form of an SMS message to the remote control of the security service directly, as well as to the owner's phone. In this case, one of the types of such devices is considered - the pyroelectric PIR-sensor, which is characterized by high efficiency and accuracy. However, the quality of the function of such models depends on many factors - from the chosen scheme for integrating the sensor into the security complex to the external conditions of influence on the structure with sensitive stuffing. It is also important to note that motion sensors are not always used as a tool to protect against an attacker. It can be installed for automatic control of individual sections of the lighting system. In this case, for example, the device will be activated when the user enters the room and also turns off when he leaves it.

Principle of operation

To understand the specifics of the operation of this device, it is worth turning to the peculiarities of the reactions of certain crystalline substances. Sensors used in the sensor provide a polarization effect at times when radiation is incident on them. In this case we are talking about thermal radiation from the human body. With a sharp change in the characteristics in the observed zone, the intensity in the electric field of the crystal also changes. Actually, for this reason, the infrared sensor PIR is also called pyroelectric. Like all detectors, such devices are not ideal. Depending on the conditions, they can trigger false signals or not identify target phenomena. However, in terms of the combination of operational properties, in most cases they justify their application.

Main characteristics

The main performance indicators that the consumer must take into account are the radii of the device and the capabilities for autonomous operation. As for the parameters for the coverage ranges, the monitored zone, as a rule, is 6-7 m. This is enough if it concerns the protection of a private house and the more so an apartment. In some models, the microphone function is also provided - in this part it is also important to determine the range, which can reach 10 m. At the same time, the PIR sensor can have direct or autonomous power supply. If you plan to organize a security system, it is better to purchase models with built-in batteries that do not require wiring. Further, the time during which the device can maintain its function without recharging is determined. Modern models do not require large power supply, therefore in the passive state they can work for about 15-20 days.

Device design

The sensor housing is usually made of metal. Inside there are two crystals - these are the elements sensitive to thermal radiation. An important structural feature of detectors of this type is a kind of window in the metal shell. It is designed to allow the radiation of the desired range. Such filtering is just designed to improve the accuracy of the crystals. In front of the window there is also an optical module in the casing, which forms the necessary wave pattern. Most often, the PIR sensor is equipped with a Fresnel lens stamped on plastic. To process the electrical signals and cut off the noise, a field effect transistor is also used. It is located near the sensitive crystals and, in spite of the problem of clipping, in some models can lower the efficiency of the crystal function.

GSM system in the sensor

This option can be called redundant, although there are many adherents of such a concept. The essence of combining the motion detection function with the sensor and the GSM module is due to the desire for complete autonomy of the device. As noted above, the sensor communicates with the central control panel, from which the signal to the operative security complex or to the phone of the direct owner subsequently emanates. If a PIR motion sensor is used with the GSM system, the alarm can be sent immediately when the penetration is registered. That is, the stage of signal transfer to the intermediate controller is skipped, which allows you to win sometimes several seconds. And this is not speaking of increasing reliability by eliminating additional links in the message transmission chain. What is the drawback of this solution? First, it relies entirely on the operation of GSM communications, which, on the contrary, lowers the reliability of the system, but for a different reason. Secondly, the presence of the module as such negatively affects the operation of the sensitive element - accordingly, the accuracy of fixing the penetration decreases.

Software

In complex security complexes, where intelligent controllers with a high degree of automation are used, the sensor programming software can not be avoided. Usually manufacturers develop special ready-made programs with an extensive set of operating modes. But if possible, the user can create and his algorithm of the sensor in certain conditions. It can be integrated through the official software that comes with the hardware. Usually this sets up the scheme of the device at the time of alarm recording - for example, the algorithm for sending messages is prescribed if the model has the same cellular communication module. On the other hand, home-based non-intrusive PIR-LED sensors are common, reviews of which indicate the effectiveness of informing about the operation of individual components of the lighting system. Each device has a microcontroller, which is responsible for the actions of the device in accordance with the laid commands.

Installing the sensor

The physical installation of the sensor is done with the help of complete fixatives. Usually, brackets or screws are used, fixing not the body of the detector itself, but the structure into which it is initially integrated. In fact, this is an additional frame with the holes provided for twisting. But the main thing in this part of the work is to correctly calculate the position of the sensor. The fact is that the infrared motion sensor PIR shows the greatest sensitivity in situations when an object with thermal radiation crosses the field of control from the side. Conversely, if a person goes directly to the device, then the ability to fix the signal will be minimal. Also, do not place the device in places that are constantly or periodically exposed to temperature fluctuations due to the operation of heating equipment, the opening doors and windows or the operating ventilation system.

Sensor connection

The device must be connected to the main relay of the controller and the power supply system. On a typical device, a card with terminals for the power supply is provided. The source with a voltage of 9-14 V is most often used, and the current consumption can be 12-20 mA. Generally, manufacturers indicate electrical characteristics by marking the terminals. Connection is carried out according to one of the standard schemes taking into account the features of operation of a particular model. In some modifications, it is possible to connect a PIR sensor without wiring, that is, directly to the network. This is in some way combined structures that are installed in open spaces and control the same lighting systems. In the case of installing a security sensor, this option is unlikely to be appropriate.

Nuances of operation

Immediately after installation and connection, the device should be set to the optimum operating parameters. For example, the sensitivity can be adjusted, the range of radiation coverage, etc. In the latest programmable modifications, it is also possible to automatically correct the parameters of the sensor depending on the operating conditions. So, if you connect the PIR-sensor to the central controller connected to thermostats, the sensor element can vary the limits of the critical radiation indices based on the obtained temperature data.

Sensor in the Arduino system

Complex "Arduino" is one of the most popular control systems for home automation. It is a controller to which light sources, multimedia systems, heating appliances and other household appliances are connected. Sensors in this complex are not final functional devices - they only serve as indicators, depending on the state of which the central unit with the microprocessor makes a decision in accordance with the embedded algorithm. The PIR sensor "Arduino" is connected through three channels, among which the digital output signal, as well as power lines with different polarity - GND and VCC.

Popular models of PIR-sensors

Most sensors are mainly manufactured by Chinese manufacturers, so it is worth to prepare for problems with electrical stuffing. To get a really high-quality sensor, it is possible that, in complete with the controllers. Nevertheless, many praise the motion sensor PIR MP Alert A9, which, although it represents a budget segment, but it has a decent build and good working qualities. In their own interest, and such models as the Sensor GH718 and HC-SR501. These are open type sensors that can be easily disguised or included in the complex of the same controller. With regard to operational properties, the radius of coverage of the described models is 5-7 m, and the battery life - an average of 5 days.

How much does the device cost?

In comparison with the price tags of modern alarm equipment, the sensor looks very attractive. In total for 1,5-2 thousand rubles. You can buy a high-quality model and even with an expanded bundle. On average, a simple PIR-sensor is estimated at an amount not exceeding 1 thousand. Another thing is that there is no question of reliability and durability in this case. In this case, do not think that this component will cost inexpensively as part of an integrated security system. Even securing a small private house can require the use of a dozen of these sensors, each of which will also need ancillary equipment for installation and connection.

Conclusion

The entry of sensory components into security systems radically changed the principles of their work. On the one hand, the detectors allowed to raise the safety of the serviced object to a new level, and on the other, complicated the technical infrastructure, not speaking about the control system. Suffice it to say that the PIR-sensor Arduino fully reveals its capabilities only under the condition of programming for automatic operation. Moreover, it interacts not only with direct registers of the intrusion signal, but also with other sensitive elements that increase its effectiveness. At the same time, manufacturers seek and facilitate the tasks of the users themselves. To do this, devices that work without wires are developed, sensor control modules with smartphones, etc., are introduced.