Classroom lighting energy-saving control system

Abstract: In today's increasingly energy-intensive environment, energy conservation and emission reduction have become particularly important. In order to advocate this concept, a classroom lighting control system was designed. The system uses STC89C51 single-chip microcomputer as the control core, and uses pyroelectric infrared sensor, light intensity detection module and counting module as the front-end signal acquisition unit. The MCU will comprehensively control the brightness and darkness of the fluorescent lamps in the classroom according to the input infrared signal, light intensity signal and number of people signals, so as to achieve the purpose of energy saving and emission reduction.

Everyone may have seen various energy-saving products in their lives, such as energy-saving lamps, inverter air conditioners, solar street lamps, and low-power LCD TVs. But for students, there are few energy-efficient applications on campus. Coupled with the extensive power management mode, the waste of electrical energy is everywhere. Classroom lighting consumes most of the electricity used in the campus. Therefore, considering how to minimize the use of classroom lighting, it is necessary to consider how to achieve energy-saving control of classroom lighting.

The MCU replaces the computer with its low price and reliable operation to become the core of the new generation of automatic control. The system uses the single-chip microcomputer as the main control core, and applies pyroelectric infrared sensor, photoelectric detection module and counting module as the front-end signal acquisition. After the logic judgment of the single-chip microcomputer, the output signal drives the relay to realize the control of the fluorescent lamp.

1 overall system design

The system consists of seven parts. The light intensity detecting module, the pyroelectric infrared sensor and the number detecting module are used as the front end signal collecting unit, and the signal is input into the internal one of the single chip microcomputer, and the output signal is controlled by the logic of the single chip microcomputer to control the relay, thereby controlling the brightness and darkness of the fluorescent lamp. If you need to turn off all lights or illuminate in an emergency, press the force button to turn all lights on or off. And the force button does not affect the normal operation of the system. The overall block diagram of the system is shown in Figure 1.

Figure 1 System block diagram

Figure 1 System block diagram

1.1 Light intensity detection circuit

A photoresistor is a component whose resistance changes as the external light intensity changes. The illumination is enhanced, the resistance is reduced, and vice versa. The light intensity detection circuit is designed using this characteristic of the photoresistor. When the light is on, the triode is turned on, outputting a low level, and vice versa. The light detection circuit is shown in Figure 2.

Figure 2 Schematic diagram of the light detection circuit

Figure 2 Schematic diagram of the light detection circuit

1. 2 infrared signal detection circuit

The pyroelectric infrared sensor is used as the human position signal detector of the system, and the pyroelectric infrared processing chip BISS0001 is used. The chip has high performance sensing signal integration processing capability. It is equipped with a pyroelectric infrared sensor and a small number of components to form a passive pyroelectric infrared measuring module. With the Fresnel lens, it is possible to detect a cone of 150 degrees, and the line detection distance is about 5 meters.

1. 3 counting circuit

In order to judge whether the student enters the classroom or walks out of the classroom, the counting circuit uses two sets of signal modules. One is mounted on the outside wall and one is mounted on the wall inside the door. The installation direction is parallel to the wall surface. In this way, counting can be achieved by detecting which sensor first signals and then detecting whether another sensor has a signal. If it is a prior signal outside the door, the later signal in the door indicates that someone has entered the classroom; otherwise, someone has left the classroom. The number of people remembered is registered in the MCU for use.

The circuit uses a laser head and a set of light intensity detection circuits to form a counting module, so that the light from the laser hair is directly incident on the photoresistor of the light intensity detecting circuit. If someone passes the door, it will block the laser light from the laser hair, and the light intensity on the photoresistor will change, thus generating a signal to the microcontroller. The schematic diagram is shown in Figure 3.

Figure 3 Counter installation diagram

Figure 3 Counter installation diagram

1. 4 output drive circuit

To control a 220 V AC fluorescent lamp, the relay must be used to isolate the strong and weak electricity to ensure safety. The working voltage of the relay is 12 V DC. In order to prevent the interference generated by the MCU system when the driving part is working, the optical isolation is added after the output buffer unit 74HC244. The relay working coil generates a counter electromotive force when the power is off, and a freewheeling diode is needed to prevent possible interference to the system.

1. 5 power module

The power circuit of this system is only a brief introduction because of its mature technology. The AC 220 V is reduced to 15 V and 6 V through the transformer, then converted to DC through the rectifier bridge, and then regulated by capacitor filtering and LM317 to DC 5 V and DC 12 V for use with microcontrollers and relays.

2 hardware overall circuit

The overall hardware circuit of the system mainly includes the following parts: light intensity detection, counting, infrared signal detection, photoelectric isolation part, output drive part, display output part. The overall circuit is shown in Figure 4.

Figure 4 system overall circuit

Figure 4 system overall circuit

The selection of the single-chip microcomputer should be carried out according to the controlled object. Since the control fluorescent lamp does not occupy too many input and output ports, the space occupied by the program is not large, so the selection of the 51 series single-chip microcomputer can meet the requirements. The serial communication between the microcontroller and the computer uses the MAX232 chip, which is a low-power level-shifting chip designed specifically for the computer's RS-232 standard serial port.

Isolation is very necessary for the MCU working around the strong power, which can reduce the interference of the strong power to the MCU. The optical isolation chip TLP521-4 is an optocoupler that can achieve signal isolation between the front end and the load side, which can enhance the safety of the circuit and reduce interference.

The output driver section uses the 74HC244 chip and the ULN2003 chip.

Both chips have the ability to enhance the load capacity of the microcontroller.

The display section consists of two 8-segment LED digital display tubes that show the number of people in the classroom in real time.

3 system programming

From the perspective of energy saving, the system can control the lighting conditions of the classroom according to the light intensity, the number of classrooms and the location of the person.

For example, if there are three lights in the classroom, when there is no external forced condition interruption, the light intensity is dark and the infrared sensor detects that someone enters the classroom and can light up. When there were no people in the classroom at first, all the lights would not light up. When the number of people is greater than 0 and less than 5, the lights in area 2 are forcibly lit. When the number of people is greater than or equal to 5 and less than 9, the light of which area is lit is determined according to the position of the person detected by the infrared sensor. When the number of people is greater than or equal to 9, all lights are illuminated. When the number of people is reduced to less than 9 and greater than or equal to 5, the infrared detection in the third area is for some time. If there is no one, the light in the third area will be extinguished. If there is someone, the light in the first area will be extinguished. When the number of people is less than 5, all the lights except the second lamp are turned off.

When the number of people is zero, all lights go out.

When there is an external interrupt, one interrupt will light all the lights, and once again the interrupt will return to its original state. The program flow chart is shown in Figure 5.

Figure 5 program flow chart

Figure 5 program flow chart

4 Conclusion

The system has been tested to meet the design requirements and has broad application prospects. It is not only suitable for classrooms, but also for places where people are concentrated in the venue, waiting room, etc., and can also be used as a Building Lighting control system. With a little change, you can adapt to lighting control in many situations. In the future, multiple systems can be centrally controlled by the upper computer, and the power coordination and distribution function can be added to better achieve the purpose of saving energy.

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