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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Pyroelectric signaling device in the security system. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling Pyroelectric infrared radiation sensors have a fairly high sensitivity, are easy to connect and relatively inexpensive. However, as practice shows, often cheap sensors are prone to spontaneous (false) alarms. Thus, the most affordable and widely used sensors "SRP PLUS" gave an average of one or two false positives in about eight hours. For this reason, the use of pyroelectric sensors in security systems requires the adoption of measures to combat false alarms. The device described below allows you to successfully use almost any pyroelectric sensor for reliable protection of the premises. The sensor is an independent electronic unit, to which a supply voltage of 12 V is connected. In the absence of movement in the sensor's field of view, the resistance between the "Relay" terminals is minimal (several tens of Ohms - "contacts are closed"), when triggered, it increases to tens of mOhm ("contacts open"). The minimum response time of the sensor is 2...3 s, even if the object moves quickly in the sensitivity zone. For occasional false alarms, this time is usually not exceeded. If the object moves in front of the sensor for a longer time, then the "Relay" outputs can be in the "open" state all this time or periodically close and open, if the object enters the zone, then leaves it. Range and field of view depend on the type of sensor. In particular, the "SRP PLUS" device has a range of up to 15 m, and an angle of 90 degrees. After power-up, the sensor does not react to any objects for 30 seconds. This allows the person who turned on the security system to leave the premises without fear of its premature operation. The principle of operation of the electronic unit, working in conjunction with the sensor, is based on the fact that the actuating device of the security system does not turn on immediately after the "Relay" circuit is opened, but only when the duration of the open state reaches 6..8 s or the circuit opens twice in for a certain time. Since the system will then operate with a delay, it is necessary to take this circumstance into account when positioning the device in such a way that it has time to confidently respond to the presence of an unauthorized person.
The schematic diagram of the node is shown in fig. 1. When the power is turned on, the R1C1 circuit generates a low-level pulse, due to which a high-level pulse appears at the output of the logic element DD2.3, setting the counter DD4 at the input R to the zero state, and the trigger on the elements DD2.1, DD2.2 - to the state , at which its upper output according to the circuit will have a low level. A single level from the lower output of this trigger disables the counter DD3. At the lower inputs of the DD2.2 element and the input C of the DD4 counter, there is a low level, since the output terminals R ("Relay") of sensor B1 are closed. The trigger on the elements DD5.2, DD5.3 will also be set to a state in which the transistor VT1 is closed and the relay K1 is de-energized, the contacts K1.1 that control the actuator are open, the HL1 indicator is off. When the pyroelectric sensor B1 is triggered, its output circuit opens and a high level is set at the two lower inputs of the trigger element DD2.2, which switches the trigger to the opposite state. At the input R of the counter DD3 will be set to a low level. The counter will start counting the pulses coming from the generator on the elements DD1.1, DD1.2. With the arrival of the eighth pulse, a high level will appear at the output 23 of the counter. If at the same time there is also a high level at the lower input of the DD1.3 element, i.e. the sensor output continues to be open, then the DD1.3 element will go to the zero state, which will lead to switching the trigger DD5.2, DD5.3, the relay will operate K1 and closing contacts K1.1, the HL1 LED will turn on. If the sensor output is closed by this moment, then the element DD1.3 will not switch. The counter DD3 will continue counting pulses and after 64 cycles a high level will appear at its output 26, which will switch the trigger DD2.1, DD2.2 to its original state. If during this time the sensor works twice, a high level will appear at the output 2 of the counter DD4, which will also switch the trigger DD5.2, DD5.3 and the contacts K1.1 will close. In the case when the sensor generates only one pulse, on the sixty-fourth cycle, the counter DD4 will be reset by the pulse that has passed through the diode VD2. The device can, if necessary, be forced to switch to the ready state at any time by pressing the SB1 button. You can power the node from an unstabilized 12 V source. All microcircuits are powered by an internal stabilizer DA1. The system response delay, as mentioned above, is more than 30 s. If it is necessary to double the delay, you need to replace the resistor R1 with another - with a resistance of 3 MΩ and capacitor C1 - with a capacity of 30 microfarads. The capacitor should be selected with a minimum leakage current. The electronic assembly is assembled on a printed circuit board made of 1,5 mm thick fiberglass laminated on both sides.
The drawing of the board is shown in fig. 2. All parts are located on the board, except for sensor B1. The node used resistors MLT-0,125; oxide capacitors for a voltage of at least 16 V, for example, K50-35 or others like that. Diodes can be replaced with KD521, KD522 with any letter index. Instead of the KT972A transistor, you can use KT972B, 2SD1111 or, in extreme cases, from the KT815, KT503 series. Microcircuits can be replaced with similar K1561 series or use imported ones: K561LE10 - CD4025, K561LA9 - CD4023, K561LE5 - CD4001, K561IE16 - CD4020, K561IE11 - CD4516. Relay - RES49, version RS4.569.425 (or RS4.569.431) or according to the new classification RS4.569.421-02 (or RS4.569.421-08), as well as any other, suitable in size and reliably operating at a voltage of 12 V. Voltage stabilizer 7809 can be replaced by KR142EN8 with the letter index A or G. On the basis of the pyro-sensor and the described assembly, a security system was assembled for a private house under construction. The future owner lived a five-minute walk from the construction site, and it was necessary to somehow notify him of the system being triggered. It was decided to use a mobile phone for this. The result is an interesting device that can be used in many other situations. Mobile phones are now very common, many serviceable ones have already fallen into disuse. Any low-cost mobile device with a minimum set of functions will be suitable for the system, and it remains suitable for its intended use. This system, when the sensor is triggered, provides communication with another mobile or regular phone, preferably with caller ID. To work together with a mobile phone, the electronic node can be simplified by removing the trigger DD5.2, DD5.3 from it.
The modified part of the circuit is shown in fig. 3. The principle of operation of the node remains the same. K1.1 contacts are soldered in parallel with the contacts of the Yes (hook up) button of the mobile phone. When the sensor is triggered, the relay contacts close the button outputs, and the phone makes a call to the number pre-set in the menu. The phone itself, with a mains power supply connected to it, is placed in a small box along with the node board and the pyro-sensor. The sensitive element of the sensor must protrude from the box. The LED in the sensor should be disabled by removing a special jumper (as described in the instructions attached to the sensor). To put the system into action, first, without connecting the node to the power source, turn on the mobile phone (it has its own battery) and enter the number to which it will call in its phone book. The cursor is placed on this number, all that remains is to press the 'Yes' button and the phone will start dialing it. Next, power is supplied to the electronic unit, the box is left in a pre-prepared inconspicuous place, pointing the sensor to the security zone, and they leave. the frequency of the clock generator DD1.1, DD1.2 with the values of the resistor R2 and capacitor C2 indicated on the diagram is about 1 Hz. It follows that the minimum duration of the open state of the sensor output, at which the alarm - about 8 s, and the time during which two pulses from the sensor can pass is about 64 s, respectively.If necessary, you can change this time by changing the clock frequency of the generator. Author: I. Korotkov, Bucha, Kyiv region; Publication: cxem.net
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