Design of LED intelligent street light system controlled by single chip microcomputer

Abstract: This control system uses STC89C58RD single-chip microcomputer as the controller, and is mainly composed of constant current source circuit, clock timing circuit, display circuit, photosensor circuit, infrared receiving circuit, sound and light alarm circuit, etc. It can set the time for street lights (LED) to turn on and off (using LED12864 to display relevant information). The street lights (LED) work normally through the constant current source circuit, and will not burn out even if they encounter short circuits, unstable voltage, etc. The circuit plays a constant current protection role. When the system encounters changes in the brightness of the environment, the street lights will automatically turn off and on, and automatically adjust the lighting conditions according to the traffic conditions on the road, and it has a timing function.

0 Introduction

With the development of digital technology and network technology, the digitization and networking of street lamps have become an inevitable trend. Saving energy, ensuring the life of lamps, improving the level of lighting management, beautifying the city night and ensuring the safety of night travel in the city have become a basic requirement for the lighting system. With the continuous development of social civilization and the rapid expansion of urban scale, urban lighting is no longer limited to road lighting. The society's requirements for lighting rate, accuracy of switching lights, real-time fault detection and timely maintenance, and energy saving of street lamps are also increasing. With the expansion of cities and the rapid growth of the number of street lamps, manual control methods are increasingly unsuitable for urban development in terms of real-time fault monitoring and processing, on-demand control, and energy saving. Therefore, the intelligent control and energy-saving measures taken for street lamps are very meaningful.

The LED intelligent street light control system designed in this paper uses the STC89C58RD microcontroller as the dominant control chip. It can realize a series of intelligent behaviors such as clock-timed switching of lights, switching lights on and off according to changes in ambient light, automatically adjusting the lighting status according to traffic conditions, and implementing sound and light alarms when street lights fail.

1 Overall system design

The system uses a photodiode to detect changes in ambient light and an infrared transmitter and receiver as a device to automatically adjust the light according to traffic conditions. The infrared transmitter is installed on the street light pole and the infrared receiver is installed on the street light bracket. When the photodiode cannot detect the light source and the infrared receiver detects the infrared signal, the street light will light up, otherwise it will not light up. Programming is used to achieve timing, design the time for turning on and off the street lights, select LCD12864 as the display device, and make corresponding displays. The system structure block diagram is shown in Figure 1.

Figure 1 System structure diagram

2 Unit module design

2.1 Clock timing part

The STC89C58RD chip we chose has a programmable timer/counter, which can be programmed by software to achieve timing/counting. When the set time is reached, the corresponding timing setting task will be executed.

2.2 Photodiode part

This circuit uses a photosensitive diode as the main control element (see Figure 2). When there is no light, the reverse resistance is large and the reverse current is small. When there is light, photons hit the vicinity of the PN junction, and electron-hole pairs are generated near the PN junction. They move in a directional manner under the action of the electric field inside the PN junction, forming a photocurrent. The stronger the light, the greater the photocurrent. Therefore, different voltage signals are output according to the brightness of the environment.

Figure 2 Photosensitive circuit

2.3 Infrared receiving and transmitting part (detecting traffic conditions and street lights on and off)

As required, infrared receivers are installed on the lamp posts on both sides of the road (see Figure 3). The receiving end of the signal is connected to the microcontroller. When a vehicle or pedestrian passes by, the receiver detects the infrared and the signal end detects the high-level input, thereby controlling the on and off of the street lights.

Figure 3 Infrared emission sensor

2.4 Sound and light alarm part

When the street lamp fails, LED0 lights up and the buzzer sounds, achieving the sound and light alarm function (see Figure 4). When the microcontroller P0.7-pin is given a high frequency, LED0 lights up, the transistor is turned on, and the buzzer also sounds.

Figure 4 Sound and light alarm

2.5 Display

This part uses LCD128*64 as the display (see Figure 5). The main reason for using this display is that it can display pictures and characters. It has very powerful functions and can control the entire circuit through display prompts.

Figure 5 Display circuit

2.6 Constant current source part

This circuit provides a constant current (see Figure 6). Q3 is connected to the load to make the load work stably. Increasing the load will not affect the change of current.

In this way, the connected street lamp can work stably. By adjusting the input voltage, the output current can be changed accordingly. The reference voltage of the collector C of the TIP122 Darlington tube can be l2-20V.

Figure 6 Constant current source circuit

2.7 Street light quality detection part

This circuit uses two voltage comparators built with an LM358, which can detect the quality of the two street lamps at the P1 and P2 ends respectively. When the street lamp is turned on, there will be voltage at the 2nd and 6th pins of the comparator, and the 3rd and 5th pins of the comparator adjust the voltage through the sliding resistor, and the adjustment voltage of the 3rd and 5th pins should be smaller than the working voltage of the 2nd and 6th pins respectively, but it cannot be adjusted to 0 V. Therefore, when the street lamp is working normally, the P0.5 and P0.6 pins of the microcontroller output low level, and when the street lamp is faulty, the P0.5 and P0.6 pins will output high level.

3 System Software Design

The system software block diagram is shown in Figure 7.

Figure 7 System software block diagram

4 System Test Results

The test results of the voltage and current at the output end of the LED street lamp drive current are shown in Table 1 and Table 2.

Table 1 Load 1 (one lamp)

Table 2 Load 2 (two lamps)

5 Conclusion

This paper proposes a design scheme of intelligent control system for street lamps based on single chip microcomputer, and completes the design of hardware and software. The intelligent control device can automatically adjust the lighting status according to the traffic conditions: when vehicles or pedestrians approach the street lamps, the street lamps gradually become brighter; when vehicles or pedestrians move away, the street lamps automatically dim and finally go out. The controller can also independently control the on and off time of each street lamp. The system has high overall cost performance, low maintenance cost, low power consumption, environmentally friendly process, and meets the requirements of green economy and conservation-oriented society.