Design and implementation of a high performance infrared signal detection switch

The four-element infrared detector uses photosensitive elements, and the alarm is triggered only when each detector detects a signal. It has stronger anti-false alarm capability and better detection performance than ordinary two-element infrared and curtain-type detectors. It has the ability to identify the intrusion direction. If the user breaks into the warning area from the inside to the outside, the alarm will not be triggered. Only illegal intrusions from the outside will trigger the alarm, which greatly facilitates the user's activities in the fortified warning area without triggering the alarm system, truly achieving "zero false alarm". In addition, it has very few peripheral devices, saving space, cost and debugging time, and improving the reliability of the whole machine.

　　l Infrared acquisition module

　　Infrared detector is a radiation energy converter, mainly used to convert received infrared radiation energy into other forms of energy such as electrical energy, heat energy, etc. that are easy to measure or observe. The dual-element detector contains two units, which are connected with reverse polarity to the common FET output, but the quad detector contains four units, two outputs, and the two independent channels enable signal processing to avoid false alarms. It is characterized by low noise, high responsiveness, excellent common mode balance, dual unit type, various filter windows for broadband or narrowband applications, single or dual channel devices, and unit devices with thermal compensation. The quad infrared detector model Lhi807 is used here, and its reliability and other indicators are far higher than the dual detector.

　　2 Signal Processing Module

　　The four-element infrared detector provides multiple segmented detection areas. An alarm signal is generated by the accumulation of all infrared energy in each area. It divides a human target into 4 to 8 areas to produce clear and strongest signals to achieve stable detection. Local temperature changes, such as those caused by mice and curtains, only affect one or two areas at the same time, thus generating smaller detection signals. These signals are then analyzed by the signal processing circuit to obtain more accurate detection and filter out false alarm signals, as shown in Figure 1.

　　Signal sampling affects the actual application value of the circuit for the accuracy of signal processing. Here, Ni's TI5000 series DSP5402 is used, which is packaged in a 68-pin PLCC package and has a 10-bit A/D converter inside. Therefore, the A/D converter is omitted in the hardware circuit, and a higher resolution can be obtained.

　　3 Overall hardware circuit

　　The hardware part of the system is mainly composed of front-end input circuit, sampler signal processing and peripheral circuit. The overall circuit is shown in Figure 2.

The PIR sensing signal is amplified at the second level, and then compared with the window voltage to determine whether it is triggered. If it is, it outputs a high level. At this time, the timer is controlled to start timing and enter the delay state. When the PIR detection signal time is greater than 768T (clock cycle), it outputs a high level to prevent false triggering. The internal output controller is equivalent to the function of an AND gate. Only when the photoresistor CDS detects the timing output and the zero-crossing detection is high at the same time, it will output a positive pulse to control the thyristor action. The photosensitive element cadmium sulfide CDS is connected to the internal Schmitt trigger. During the day, the CDS resistance is low, the Schmitt output is low, and the output is inhibited; on the contrary, when the PIR works, the CDS does not work, that is, the I/O pin detects that the CDS outputs a low level. Due to the role of RE200B zero-crossing detection, a standard starting point is the zero-crossing voltage. When pins 1, 2, and 3 are high at the same time, pin 11 outputs a positive pulse to control the operation of the peripheral circuit. The 15-pin TCI is the timing clock, and the 19-pin TB is the system clock. The time setting is: F = (1 ± O.2) / 1.1RCo. The load can continue to work if the human body has a slight movement in the sensing range of the switch. When the human body is stationary for more than the delay time, the switch will automatically turn off. Once the human body moves, the load will automatically turn on again. Since the circuit uses zero-crossing technology, it is often on and off, and has little effect on the load. If this switch is installed during the day, the light bulb will flash 3 times and then go out, indicating that the initialization is completed and the normal monitoring state is entered. If this switch is installed at night, the load will work immediately, and the load will automatically turn off after the person leaves.

　　4 Performance Testing

　　The simulation software Matlab was used to simulate the daytime and nighttime conditions, and the simulation diagrams are shown in Figures 3 and 4. Figure 3 is the simulation result of the binary pyroelectric infrared signal processor, and Figure 4 is the simulation result of the quaternary pyroelectric infrared signal processor. It can be seen from the figure that the quaternary pyroelectric infrared has a better response speed.

　　5 Conclusion

　　With the improvement of people's safety awareness, more and more people are investing in the research of safety technology, and the application of multi-element infrared detector sensors has gradually become a hot topic. Based on a comprehensive discussion of pyroelectric infrared sensors, the hardware structure design of a four-element pyroelectric infrared signal processor is given, and finally a detailed data simulation is performed using Matlab software. It can be predicted that the development of this type of system will surely promote the industrialization of safety technology more quickly and has certain economic significance.