1. Introduction
Functional switches play an important role in people‘s production and daily life. There are various types of automatic power off switches, voice controlled switches, and infrared induction switches available on the market.
At present, research on the power outage switch for incoming calls mainly involves two aspects: one is to directly use the series parallel relationship of the switch and the role of the relay to achieve automatic power outage function after power outage. This scheme has a lower cost, but the switch volume is larger; The second is to use digital circuits for programming to achieve automatic power outage, with stable switch performance, small size, but high cost. The research on infrared induction switches at home and abroad is relatively mature, generally using chips such as BISS0001 and CSC9803 to process the received infrared induction signals. These chips have powerful functions but have many pins and complex peripheral circuit connections. Although both of the above switches have some related invention patents in China, there is currently no energy-saving switch that combines the two functions. So we designed an infrared power outage automatic energy-saving switch that combines the two switch functions mentioned above. We used two relays in series to achieve the power outage function, and processed the infrared induction signal using LM324 chip, making the switch smaller in size and lower in cost; Fill the gap in this field domestically and respond to the call for energy conservation. This switch can be used in places such as student dormitories and homes.
2. Circuit schematic and design
The block diagram of the switch function implementation is shown in Figure 1.
Figure 1 Switch Function Implementation Block Diagram
The overall design concept of this switch is to use a low voltage (5V) to control the high voltage (220V) part, while the low voltage is obtained by transforming the high voltage. The switch mainly consists of power supply, infrared induction control, and relay control parts. The circuit schematic of the switch is shown in Figure 2.
Figure 2 Switch schematic diagram
(1) Design of the power supply section
In Figure 2, the 220V AC power is output by the transformer coil with a 12V AC voltage, rectified by a bridge rectifier circuit composed of IN4001, filtered by a 1000uf capacitor, and stabilized by 7805 to obtain a stable voltage of 5V at both ends of capacitor C2.
And this stable voltage of 5V can provide working voltage for the infrared sensing signal control part.
(2) Infrared sensing head part
LHI907 in Figure 2 is a pyroelectric (pyroelectric) human infrared sensor head. The infrared radiation emitted by the human body at around 10um reaches the pyroelectric element, which loses its charge balance when it receives a change in the temperature of the infrared radiation from the human body and releases charges outward,. The sensor itself does not emit any type of radiation, and the device has low power consumption, good concealment, and low price. The sensitivity of infrared pyroelectric sensors to the human body is also closely related to the direction of human movement. Infrared pyroelectric sensors are the least sensitive to radial movement and the most sensitive to transverse movement, as they can only detect moving human bodies.
(3) Processing of infrared induction signals
The S-end signal of LHI907 is input to pin 3 of the integrated operational amplifier LM324. The negative feedback amplification effect of the first two operational amplifiers inside amplifies the signal by about 100 times, and then input to another operational amplifier for voltage comparison through pin 10. When there is no one, the 8-pin outputs a high level, and when there is someone, the 8-pin outputs a low level. Afterwards, the 13-pin is connected to the operational amplifier for RC delay. When pin 8 is at high level and pin 13 is at high level, a low level is output at terminal 14 through the voltage comparison of operational amplifier 4. When pin 8 outputs at low level, capacitor C7 is discharged through IN4001. At this time, pin 13 is at low level and pin 14 is at high level, and then pin 8 immediately returns to high level. At this time, the power supply charges C7, but pin 13 remains at low level. After charging, pin 13 becomes high level and pin 14 becomes low level. This delay function test measured approximately 30 seconds, during which time 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 according to different occasions to achieve different delay times.
(4) Relay control part
K1 and K2 in Figure 2 are normally open relays. Due to the high-voltage AC power supply and the low-voltage DC control part, the transistor in the figure uses 9014. Its function is to control the working status of relay K2 through the input signal of LM324‘s 14 pin. Since the signal of 14 pin cannot directly drive K2 to work, the design of 9014 is still necessary.
(5) Peripheral circuit of the switch
The nodes P1, P2, P3, and P4 in Figure 3 correspond to the P1, P2, P3, and P4 nodes in Figure 2. This way, the switch can control the off and off states of the light bulb, thereby achieving the goal of energy conservation.
Figure 3 Switch Peripheral Circuit
3. Working principle of the overall circuit
A state: When the circuit connection is correct and working normally, the switch is connected to the D end of LHI907, relay K1 works, causing the contact to be connected. At this time, the power supply is to the human infrared sensing circuit, and the infrared sensing works normally. Relay K2 can be controlled to act by detecting the presence of no one. At this point, a single action of manual switch SW can directly cut off the power supply of infrared sensing, thereby unconditionally terminating the operation of relay K2. Another action of SW can switch to infrared monitoring status.
Status B: When the break point occurs in the working state, relay K1 stops working. When there is another power call, relay K1 cuts off the power supply to the 9014 transistor collector, so relay K2 does not work. When SW acts once, K1 works to achieve the relay‘s self-protection function. When SW acts again, it can return to the working state in A. Thus, the function of turning off the lights when leaving and automatically powering off incoming calls after a power outage is achieved, achieving the effect of saving electricity.
4. Result analysis
Make the actual circuit and measure the working condition of the light bulb in each state of the switch, as shown in Table 1:
So the entire switch has achieved the functions of "people leaving the light off, people coming the light on" and automatic disconnection after power outage.
5. Conclusion
This article designs a new type of switch - a switch that combines the functions of common human infrared sensing switches and incoming and outgoing power switches. At present, there is no switch with this switch function produced in China, and its production cost is also low, with good application prospects; It can be used not only in student dormitories, but also in homes, office spaces, and other places, making installation convenient. Through extensive practical use, it has been proven that as long as the installation position of the infrared sensing head is appropriate, the switch can operate normally and reliably, playing a role in energy conservation and power outage protection.
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