Design of an infrared induction and power-off energy-saving switch

　　Functional switches play an important role in people's production and life. Various types of automatic power-off switches, voice-activated switches, and infrared induction switches are widely available on the market.

　　At present, the research on the incoming power-off switch involves two main aspects: one is to directly use the series-parallel relationship of the switch and the function of the relay to realize the automatic power-off function after the power outage. This solution has a low cost, but the switch is large in size; the second is to use digital circuits for programming to realize automatic power-off. The switch has stable performance and small size, but the cost is high. The research on infrared induction switches at home and abroad is relatively mature. Generally, chips such as BISS0001 and CSC9803 are used to process the received infrared sensing signals. These chips are powerful but have more chip pins and more complicated peripheral circuit connections. Although the above two switches have some related invention patents in China, there is no energy-saving switch that combines the two functions. So we designed an infrared incoming power-off automatic energy-saving switch that integrates the above two switch functions. It uses two series-connected relays to realize the incoming power-off function, and uses the LM324 chip to process the infrared sensing signal, making the switch small in size and low in cost; filling the gap in this field in China and responding to the call for energy saving. This switch can be used in student dormitories, homes and other places.

　　2. Circuit schematic and design

　　The block diagram of the switch function is shown in Figure 1.

　　The overall design idea of ​​the switch is to use low voltage (5V) to control high voltage (220V), and the low voltage is obtained by transforming the high voltage. The switch is mainly composed of power supply, infrared induction control and relay control. The circuit diagram of the switch is shown in Figure 2.

　　(1) Design of power supply

　　In Figure 2, the 220V AC power is output through the transformer coil to a 12V AC voltage, which is rectified by the bridge rectifier circuit composed of IN4001, then filtered by a 1000uf capacitor, and finally stabilized by 7805 to obtain a stable voltage of 5V at both ends of capacitor C2.

　　This stable 5V voltage can provide working voltage for the infrared sensing signal control part.

　　(2) Infrared sensor head

　　In Figure 2, LHI907 is a pyroelectric (pyroelectric) human infrared sensor. The infrared rays of about 10um emitted by the human body reach the pyroelectric element. When the temperature of the element changes after receiving the infrared radiation of the human body, it will lose its charge balance and release the charge outward. The sensor itself does not emit any type of radiation, the device consumes very little power, has good concealment, and is inexpensive. The sensitivity of the infrared pyroelectric sensor to the human body is also closely related to the direction of human movement. The infrared pyroelectric sensor is the least sensitive to radial movement, but the most sensitive to transverse movement. It can only detect moving human bodies.

　　(3) Processing of infrared sensing signals

　　The S-terminal signal of LHI907 is input to the pin 3 of the integrated operational amplifier LM324. The negative feedback amplification of the first two operational amplifiers inside it amplifies the signal by about 100 times, and then inputs another operational amplifier through pin 10 for voltage comparison. When there is no one, the 8-pin outputs a high level, and when there is someone, the 8-pin outputs a low level, and then connects to the 13-pin for RC delay through the operational amplifier. When the 8-pin is high, the 13-pin is high, and the voltage comparison of the operational amplifier 4 outputs a low level at the 14-pin. When the 8-pin output is low, the capacitor C7 is discharged through IN4001, and the 13-pin is low and the 14-pin is high. Then the 8-pin immediately changes back to a high level. At this time, the power supply charges C7, and the 13-pin is still low. After the charging is completed, the 13-pin becomes high and the 14-pin becomes low. This delay function test is measured to be about 30 seconds. During this period, if there is human activity and refresh delay time. This delay design solves the problem that pyroelectric sensors can only sense human movement, thereby extending the output signal time. The size of C7 can be adjusted to achieve different delay times according to different occasions.

　　(4) Relay control part

　　In Figure 2, K1 and K2 are normally open relays. Since the power supply part is high voltage AC and the control part is low voltage DC, the transistor in the figure uses 9014, which controls the working state of relay K2 through the input signal of pin 14 of LM324. Since the signal of pin 14 cannot directly drive K2 to work, the 9014 design is still necessary.

　　(5) Peripheral circuit of switch

　　The nodes P1, P2, P3, and P4 in FIG3 correspond to the nodes P1, P2, P3, and P4 in FIG2 , so that the switch can control the on and off state of the light bulb, thereby achieving the purpose of energy saving.

　　Figure 3 Switch peripheral circuit

　　3. Overall circuit working principle

　　State A: When the circuit is correctly wired and working properly, the switch is connected to the D terminal of LHI907, and the relay K1 works to connect the contacts. At this time, the power is supplied to the human infrared sensing circuit, and the infrared sensing works normally. The relay K2 can be controlled by detecting whether there is a person. At this time, the manual switch SW can be operated once to directly cut off the power supply part of the infrared sensing, thereby unconditionally terminating the operation of the relay K2. The SW can be operated again to switch to the infrared monitoring state.

　　State B: When the breakpoint is reached in the working state, relay K1 stops working. When the power comes back, relay K1 cuts off the power supply to the collector of 9014 transistor, so relay K2 does not work. When SW is activated once, K1 works to realize the self-protection function of the relay. When SW is activated again, it can return to the working state in A. Thus, the function of automatically cutting off the power when the lights are off and power is cut off after power outage is realized, achieving the effect of saving electric energy.

　　4. Results Analysis

　　The actual circuit was made and the working conditions of the bulb under various switch states were measured as shown in Table 1:

　　(Note: The state when someone approaches the infrared sensor head is recorded as the infrared sensor switch is on, and the state when someone leaves the infrared sensor head is recorded as the infrared sensor switch is off; the state of relay K2 after power failure is recorded as the off state, and the state of relay K2 after power is on is recorded as the on state.)

　　Therefore, the entire switch realizes the functions of "lights off when people leave and lights on when people come" and automatically disconnecting after power failure.

　　5. Conclusion

　　This article designs a new type of switch, which combines the functions of the common human infrared sensor switch and the incoming power off switch. At present, there is no switch with this switch function produced in China. Its production cost is also low and its application prospect is good. It can be used in student dormitories, homes, offices and other places, and is easy to install. A lot of practical use has proved that as long as the infrared sensor head is installed in a suitable position, the switch can work normally and reliably, playing the role of energy saving and power off protection.