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

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1. Introduction

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

At present, the research on incoming power-off switches 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 power failure. This solution has a low cost, but the switch is large in size; the second is to use digital circuits for programming to achieve 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 induction signals. These chips are powerful but have more chip pins and more complicated peripheral circuit connections. Although there are some related invention patents for the above two types of switches in China, there is no energy-saving switch that combines the two functions. Therefore, we designed an infrared power-off automatic energy-saving switch that integrates the above two switch functions. Two relays in series are used to realize the power-off function, and the LM324 chip is used 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 conservation. This switch can be used in student dormitories, homes and other places.

2. Circuit schematic diagram and design

block diagram of the switch function implementation are shown in Figure 1.

Figure 1 Switch function implementation block diagram

The overall design idea of the switch is to use low voltage (5v) to control the high voltage (220v) part, and the low voltage is obtained by transformer processing of the high voltage. The switch mainly consists of a power supply part, an infrared sensing control part and a relay control part. The circuit schematic diagram of the switch is shown in Figure 2.

Figure 2 Switch schematic diagram

(1) Design of the power supply part

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

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

(2) Infrared sensing head part

LHI907 in Figure 2 is a pyroelectric (pyroelectric) human infrared sensing head. 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 the charge balance and release the charge outward. The sensor itself does not emit any type of radiation, the device power consumption is very small, the concealment is good, and the price is low. 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 and the most sensitive to transverse movement. It can only detect moving human bodies.

(3) Processing of infrared sensing signals

The S-end signal of LHI907 is input to the 3rd pin 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 the 10th pin for voltage comparison. When there is no one, pin 8 outputs a high level, and when there is someone, pin 8 outputs a low level, and then connects to pin 13 for RC delay through the operational amplifier. When pin 8 is high, pin 13 is high, and the voltage comparison of operational amplifier 4 outputs a low level at terminal 14. When pin 8 outputs a low level, capacitor C7 discharges through IN4001, and pin 13 is low and pin 14 is high. Then pin 8 immediately returns to a high level, and the power supply charges C7, and pin 13 is still low. After charging, pin 13 becomes high and pin 14 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 time of the output signal. The size of C7 can be adjusted according to different occasions to achieve different delay times.

(4) Relay control part

K1 and K2 in Figure 2 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 design of 9014 is still necessary. (5) Peripheral

circuit Nodes P1, P2, P3, and P4 in Figure 3 correspond to nodes P1, P2, P3, and P4 in Figure 2, so that the switch can control the extinguishing and extinguishing state of the bulb, thereby achieving the purpose of energy saving.

Figure 3 Peripheral circuit of the switch

3. Overall circuit working principle

State A: When the circuit is connected correctly and works normally, the switch is connected to the D terminal of LHI907, and relay K1 works to connect the contacts. At this time, the power supply is for the human infrared sensing circuit, and the infrared sensing works normally. The action of relay K2 can be controlled by detecting whether there is anyone. At this time, the manual switch SW can directly cut off the power supply of the infrared sensor by operating once, thereby unconditionally terminating the work of relay K2. Operating SW again can 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 again, relay K1 cuts off the power supply to the collector of the 9014 transistor, so relay K2 does not work. When SW operates once, K1 works to realize the self-protection function of the relay. Operating SW again can return to the working state in A. Thus, the function of turning off the light when people leave and automatically turning off the power after power outage is realized, achieving the effect of saving electric energy.

4. Result analysis

The actual circuit is made and the working conditions of the bulbs in each state are measured as shown in Table 1:

Therefore, the whole switch realizes the functions of "turning off the light when people leave and turning on the light when people come" and automatically disconnecting after power outage.

5. Conclusion

This paper designs a new type of switch - a switch that combines the functions of the common human infrared sensor switch and the power-off switch for incoming calls. 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 large amount 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.

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

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