LED intelligent lighting system design

LED is called the fourth generation illumination source or green light source. The LED light-emitting device is a cold light source, which has the characteristics of energy saving, environmental protection, long life and small volume. The incandescent lamp, the tungsten halogen lamp has a luminous efficiency of 12 to 24 lm/W, a fluorescent lamp of 50 to 70 lm/W, and a sodium lamp of 90 to 140 lm/W, and most of the power consumption becomes heat loss. The LED can reach 50-200 lm/W, and the monochromaticity of the single light is good, the spectrum is narrow, and no filtering is required, and the visible light can be directly emitted. In the case of the same lighting effect, the power consumption is about one tenth of that of an incandescent lamp and one-half of that of a fluorescent lamp. The same effect of a fluorescent lamp is more than 40 watts, and the power of each LED is only 8 watts. With an average life of 100,000 hours, LEDs are safe and reliable, contain no mercury, sodium and other substances that may be harmful to health, and are environmentally friendly. They are called "green lighting sources."

2 Intelligent lighting control scheme design

The photosensitive light is used to detect the intensity of the indoor light. The passive pyroelectric infrared detector can detect the characteristics of the human body. The sensor transmits the detection data to the control core--the single-chip microcomputer , and controls the opening, closing and illumination of the lighting device according to the processing result. Figure 1 is a block diagram of the intelligent lighting control scheme.

The system is mainly composed of three parts: the sensor part, the controller part and the LED drive circuit and lighting system, as shown in Figure 1.

3 system hardware design

3.1 Sensor section

3.1.1 Passive pyroelectric infrared detector

The detector has three key components: the Fresnel filter chip, which acts as a bandpass filter through a filter chip with a cutoff wavelength of 8 to 12 μm, so that environmental interference is significantly controlled; Fresnel lens, focusing The function is to refract (reflect) the pyroelectric infrared signal on the pyroelectric infrared sensor. The second function is to divide the warning zone into several bright and dark zones, so that the moving object entering the warning zone can change with temperature. The form produces a varying pyroelectric infrared signal on the pyroelectric infrared sensor, such that the pyroelectric infrared sensor can generate a varying electrical signal; the pyroelectric infrared sensor converts the change in infrared radiation energy through the filter chip into an electrical signal , that is, thermoelectric conversion.

The human body has a constant body temperature, generally at 37 degrees, so it emits infrared light with a specific wavelength of about 10 μm. The passive infrared probe works by detecting infrared rays of about 10 μm emitted by the human body. The infrared light emitted by the human body of about 10 μm is enhanced by the Fresnel filter and collected on the infrared sensing source. The infrared sensing source adopts a pyroelectric element, which loses the charge balance when receiving the stable change of the infrared radiation of the human body, releases the charge outward, and can generate a level change after the detection process.

According to this principle, the infrared module with stable performance is applied. When someone walks, the module outputs 3.3V, and when no one is low. The module has an adjustable delay of up to 18 seconds.

3.1.2 Ambient brightness sensing module

The core device of this sensing module is a photoresistor. A resistive value of the photoresistor using the photoelectric effect of a semiconductor made with the intensity of incident light is changed resistor; incident light intensity, resistance is small, the incident light is weak, resistance increases. Photosensitive resistors are generally used for light measurement, light control, and photoelectric conversion (converting changes in light into electrical changes), as shown in Figure 2.

3.2 Control section

STC12C5628AD series MCU is a single clock /machine cycle (IT) MCU produced by Hongjing Technology. It is a new generation 8051 MCU with high speed/low power consumption and super anti-interference. The instruction code is fully compatible with the traditional 8051, but the speed is 8~12. Double, internal integration of the MAx810 dedicated reset circuit. 4-channel PWM, 8-channel high-speed 10-bit A/D conversion for motor control and strong interference.

Selecting this type of MCU mainly considers the role of PWM and AD conversion, which greatly simplifies the peripheral circuit. At the same time, the generated PWM signal can be directly connected to the driver chip, which makes the cost of this system much lower.

Since the PWM dimming method is adopted, in order to reduce unnecessary peripheral circuits, the selected driving chip can directly input the PWM square wave from the DIM pin.

The LM3407 is a pulse width modulated floating buck converter with an integrated N-channel power MOS FET designed to deliver a precise constant current output to drive high power light-emitting diodes (LEDs). A notable feature of the LM3407 is the Pulse Level Modulation (PLM) control scheme, which ensures constant current output accuracy over the entire input voltage and operating temperature range when using an external 1% precision current setting thick film resistor. Better than 10%. Another feature of the converter is that it has a DIM pin that accepts standard logic pulses and controls the brightness of the LED array, making the LM3407 an ideal device for precision power LED drivers or constant current sources.

software design

The program adopts the modular design idea, and sets two function module subroutines with the main program as the core: some functions are implemented in the subprogram, which simplifies the design structure. A function module subroutine is called by the main program during operation.

The system has two functional modules: l is an AD conversion module; 2 is a PWM generation module. It can be called directly in the main function, which greatly simplifies the design structure. The flow chart of its system is shown in Figure 6.

in conclusion

The experiment has verified that the system achieves good energy saving and improved lighting environment. It not only eliminates the problem of disturbing the people's corridors, but also solves the problem of saving energy by turning off the lights in time. The selected LED lights are called "green light sources in the 21st century."

The system has a simple structure and strong practicability. It can be applied to the corridor lights of the apartment building, the lighting of the bathroom, etc., which can achieve good lighting, energy saving and environmental protection effects. Moreover, the control card used in this design can only control the monochrome display of the display. If it can display two colors, even three colors, it is more convenient. The LED display can display changing numbers, texts and graphic images. It can be used not only in indoor environments but also in outdoor environments. It has the advantages that projectors, TV walls and LCD screens cannot match. LEDs can even be used in new technologies such as information lights, large screen displays, and backlit lights for liquid crystal displays (LCDs). It is one of the means of display for future intelligent transportation systems.

Since the analysis and design of the LED display has a lot to do with the actual application environment and application purposes, the requirements for its control system are also different. If the area requirement of the display screen is large and the amount of information displayed on the screen is too large, the amount of data to be transmitted also increases. How to design a more ideal font storage method and the compression algorithm for data transmission requires further research and discussion. .