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C8051F020-based automatic monitoring and control LED energy-efficient lighting system design

In Electronic Infomation Category: C | on April 23,2011

Abstract: A novel based on the ambient light intensity and REF02HP datasheet and temperature changes in infrared automatic switches, adjust the brightness of the LED lighting system design. C8051F020 microcontroller for system control by the core design of silicon photovoltaic cells and REF02HP price and integrated operational amplifier consisting of light intensity sensor, used as a pyroelectric infrared wireless sensor module, the use of DS18B20 for the temperature sensor, also used to achieve a working LCD information display. Experimental results show that the system power at 2 170 lx of light or temperature higher than 82.5 can automatically shutdown, when the light intensity is less than 1 040 lx or when temperature is below 49.3 automatically open; when the light intensity at 1 000 ~ 2 000 lx changes, LED brightness can automatically adjust to maintain the basic stability of the environment illumination.

LED-called "fourth generation light green light", has been gradually applied in telecommunications, transportation, agriculture, medicine, military and REF02HP suppliers and other fields. LED (Light-emitting Diode, Light Emitting Diode) is a solid state semiconductor components, able to light energy directly into electrical energy. As a solid light source, LED has a long life, high luminous efficiency, multi-light color and other characteristics, can work in a safe low voltage can also be a continuous flash switch off, to achieve 0% to 100% dimming.

This paper describes an automatic monitoring and control based on C8051F020 MCU LED energy efficient lighting design. The system LED lights can control light intensity, when the ambient light intensity automatically increase the luminous intensity of LED, when light intensity decreased to strong LED lights automatically when the luminous intensity, luminous intensity to maintain the stability of the environment and save energy effect. Meanwhile, the system also has a light intensity, temperature, infrared sensors switch 3 LED lights on and off, coupled with over-voltage, over current protection measures to further improve energy efficiency and ensure the normal operation of the lighting system. In addition, the system also uses LED lighting to achieve the work of the LCD external display of information. The system can be used as corridor lighting, task lighting, equipment, lighting, and many other occasions.

1 overall design plan

C8051F020 MCU used in this system as the core to achieve the automatic LED lighting and control, the overall framework of the system shown in Figure 1.

Figure 1, the overall framework of the system

Points throughout the system design of hardware and software design, hardware design, modules can be divided into supply-driven, automatic monitoring and control and display module 3.

Process of supply-driven module is: 12 ~ 24 V DC power input, through the over-voltage protection circuit formed after the SN3350 chips to provide a safe voltage LED driver circuit, driver circuit driving LED lights work properly. Automatic monitoring and control and display module including light intensity sensors, temperature sensors, infrared wireless sensor and LCD display. Light intensity sensor uses a silicon photovoltaic cells and integrated operational amplifier composed of photoelectric conversion circuit, the environment, light intensity is converted to voltage signal, through the microcontroller A / D conversion, based on the measured voltage and illumination curve, the corresponding voltage value into a luminance and for the LCD1602 LCD display; DS18B20 chip temperature sensor circuit used, the ambient temperature will be converted to real-time signal analysis and processing is passed to the microcontroller, the same by LCD1602 LCD display; infrared sensor used to BISS0001 core pyroelectric infrared wireless sensor circuit, sensing circuit receives the signal transmitted MCU LED lights on and off.

Energy-saving and automatic monitoring and control system functions to achieve by the C8051F020 MCU. The idea is to software programming: PWM signal generated internally by the microcontroller control chip SN3350 drive ADJ pin. By changing the PWM duty cycle to achieve any voltage on the ADJ input, then control the LED lighting, light switches and brightness adjustment.

2 Hardware Design

2.1 MCU C8051F020

The system uses microcontroller C8051F020, CIP-51 includes the chips CPU core instruction set is fully compatible with MCS-51. With 64 kB on-chip Flash program memory, 4 352 B of RAM, 8 Ge I / O ports a total of 64 I / O lines, a 12-bit A / D converter an 8-bit A / D converter and a dual 12-bit D / A converter, 2 comparators, 16-bit general purpose timers 5, 5 capture / compare modules programmable counter / timer arrays, watchdog timer, VDD Monitor, and Temperature Sensor and other parts. C8051F020 MCU supports dual clock, the operating voltage range of 2.7 ~ 3.6 V (Port I / O, RST, and JTAG pins of the voltage is 5 V).

2.2 LED driver circuit

The system chosen SN3350 chip LED driver circuit as the core. SN3350 is a continuous inductor current mode step-down driver chip for a supply voltage higher than the required voltage or a string of LED applications. Chip input voltage range * 0 V, output current up to 750 mA, output power up to 30W. Figure 2-based system uses the LED driver circuit.

Figure 2 LED driver circuit

Figure 2, 3, ADJ pin is multi-functional switch / brightness control pin, the pin characteristics are:

1) pin is left floating: work in normal mode. (Normal mode VADJ = VREF = 1.2 V, operating current IOUTnom = 0.1/R1);

2) the input voltage drops below 0.2 V: shut down output current;

3) the input DC voltage from 0.3 ~ 1.2 V: Output current adjustment range from 25 ~ 100%;

4) through different signal to control the PWM duty cycle output current;

5) When the ADJ pin voltage exceeds 1.2 V: the current is automatically clamped at 100%.

SN3350 output current can be added in the ADJ pin to set the control signal. Generated by the system microcontroller PWM signal input ADJ pin above the pin driver circuit according to the different characteristics of the voltage into the different working patterns.

2.3 light intensity sensor

Intensity of this system uses a photoelectric conversion sensor circuit, the schematic diagram shown in Figure 3. The role of the circuit is integrated operational amplifier LM324 and through the feedback resistor Rf, the silicon photovoltaic cells (the equivalent of a light controlled current source) output current is converted to voltage signal output. Rf resistance by adjusting the size, can change the size of the output voltage, which can be adapted to the input signal level control circuit voltage requirements. Practical applications, the light intensity of, Is the size, thereby causing changes in Vout, thus achieving the light intensity signal into a voltage signal.

Figure 3 photoelectric conversion circuit

Table 1 and Figure 4 is actually made in the photoelectric conversion circuit, according to meter and voltage meter measured the light intensity - voltage relationship.

Table 1 photoelectric conversion circuit test results

illumination Figure 4 - Voltage

Be seen from Figure 4, with the ambient light increases, the photoelectric conversion circuits output voltage increases linearly, correlation of 99.1% and good linearity. This indicates that in Figure 3 photoelectric conversion circuit made of the actual test results with the theoretical expectations conformity is good. Meanwhile, Figure 4 of the light intensity - voltage relationship for the software part of the linear programming provides an important basis.

2.4 infrared wireless sensor

Infrared sensor of the system as the core to adopt a BISS0001 pyroelectric infrared wireless sensor circuit. BISS0001 by the operational amplifiers, voltage comparators, state controller, the delay time and blocking time timer timers pose a number of other mixed-specific integrated circuit. To BISS0001 core pyroelectric passive infrared sensors detect the wireless mode, the circuit shown in Figure 5. Fresnel lens (DSG) received by the body into the detection region emission wavelength of 8 ~ 12 m in the infrared, through the pyroelectric sensor (PIR) optical signals into electrical signals, amplified by the circuit system, filter, and finally signal output.

Figure 5 pyroelectric infrared wireless sensor circuit

2.5 other circuit blocks

This system there are two relatively simple circuit blocks: over-voltage protection circuitry and temperature sensor circuit. The significance of

overvoltage protection. When the internal regulation loop switching power supply failure or improper operation of the user causes the output over-voltage phenomenon, over-voltage protection circuit can be protected to prevent damage to electrical equipment after class. There is also the power supply circuit in the system self-recovery fuse in series, played the role of over-current protection. The system

Dallas Semiconductor temperature sensor with a digital temperature sensor DS18B20. This is a support of the worlds first "bus line" interface, the temperature sensor. DS18B20 used for the temperature sensor circuit is very simple, nine temperature signal via a bus, passed directly to the microcontroller for processing.

3 Software Design

Software design idea is the first independent design sub-module, and then consolidate the various modules. The system programming flow chart shown in Figure 6.

Figure 6, the flow chart of system programming

Program is divided into five modules: the brightness control module, the temperature detection processing module, the light intensity detection processing module, infrared wireless detection processing module, LCD module, the following more complex for the first 3 minutes and state of the module.

1) brightness control module LED driver according to the given pin circuit chip SN3350 features, you can control the ADJ pin voltage signal to control LED brightness. SCM 80C51F020 to self-generate Vpp = 5 V of the PWM signal, so you can control the duty cycle of the PWM signal to control the brightness of LED lights. The light intensity according to Figure 4 - Voltage line set to determine procedures, obtained the corresponding duty cycle, can be achieved for the brightness control.

2) temperature probe DS18B20 chip processing module as output signal output pin is a digital signal, the contents of this module is mainly obtained from DS18B20 decoding digital signals, to obtain the actual temperature values.

3) light intensity detection processing module in Figure 3 photoelectric conversion using ambient light intensity detection circuit output voltage signal. This signal is an analog signal, therefore, need to convert this analog to digital signals only after enough single chip for processing. 80C51F020 comes with A / D converter module, analog to digital conversion can be achieved. Light corresponding to the voltage signal between 0 ~ 2.4 V, so the value of a particular voltage to convert to 8 bit digital signals, then similar treatment with the temperature signals to control light.

According to the article described in section 2.2 SN3350 ADJ pin-side driver IC control features, program design specific programs are as follows:

LED lamp illumination with the automatic adjustment of the external environment and control: When the actual measured light intensity is greater than 2 000 lx (self-illumination value can be set according to need, the same below), the Order ADJ pin input voltage is 0, LED off; when the actual measured less than 1 000 lx illumination, let the ADJ pin input voltage is 0.3 V, LED light; When measured the actual light intensity is greater than 1 000 lx and less than 2 000 lx, the order cited ADJ pin input voltage between 0.3 ~ 1.2 V make the appropriate changes.

LED lights with automatic adjustment of the external environment and control of temperature: When the LEDs temperature is higher than 80 (temperature value can be based on need to set their own, the same below), the so VADJ = 0; when the LED temperature of less than 50 , so VADJ = 1.2 V.

LED light with infrared radiation signals outside the automatic adjustment and control: When the pyroelectric infrared sensor when the sensing signal came, so VADJ = 1.2 V, no signal came, the order VADJ = 0.

4 System Test

4.1 Basic operation test

Power supply 15 V; measured three LED lights at both ends of the working voltage is 14V; drive circuit output current is 320 mA; overvoltage test regulation when the input voltage is greater than 24 V, LED drop voltage across quickly; When the input voltage is increased to 27V when the voltage across the LED has dropped to 0V.

Test results show that the system can work under low normal and stable, with overvoltage protection.

4.2 functional testing

1) measurement and display capabilities

Can display environment light intensity: energy, LCD display light intensity can be accurate to 1 lx;

Can display temperature: can, LCD displays ambient temperature can be accurate to 0.1 ;

2) automatic control functions

Light intensity changes can switch lights: energy, light levels at 2 170 lx automatically turn off the lights; light intensity is less than 1 040lx automatically turn off the lights (design threshold values ??were 2 000lx and 1 000 lx); < / P>

Temperature changes can turn off the lights: energy, temperature higher than 82.5 automatically turn off the lights;

Temperature below 49.3 automatically turn on the lights (design threshold values ??were 80 and 50 );

Ability to maintain the basic stability of light intensity: energy, environment, light intensity, but not less than 1 000 lx, automatically increase the luminous intensity LED; light intensity increased, but not more than 2 000 lx, automatically reduced LED luminous intensity;

Infrared sensors and can switch lights: Yes, some people enter the LED lights in the distance (3.5 m at the maximum radius), the automatic lights, and after 10 s to maintain light levels gradually decreased until the close.

Test results show that the system has with the light intensity, temperature, infrared radiation changes in the automatic control switch, regulating the function of light intensity, the measured data and theoretical values ??match fairly well designed.

5 design problems that need attention

The system is characterized by more hardware module circuit design should pay attention to a total match with the interface. Specifically, the MCU C8051F020, LED drive circuit of the SN3350 chips, photoelectric conversion circuit in the integrated operational amplifier LM324, pyroelectric infrared wireless sensor core BISS0001 circuit chip, DS18B20 temperature sensor circuit and overvoltage protection circuit module 6 common ground with the DC power supply. Interface matching problem mainly in the light intensity, infrared radiation, the temperature sensor output 3 the input of the microcontroller and the microcontrollers output port and LCD LCD1602, LED Driver IC SN3350 control pins. In addition, LM324, BISS0001, DS18B20 other chip operating voltage 5 V, LED lighting system is less than 15 V operating voltage, the test subject received 5 V power supply, but the actual production of finished products when you need to add a level conversion circuit will be unified into 15 V supply voltage 5 V regulator output to the relevant chips.

Should be considered in the preparation of program information is sent by each sensor microcontroller processing priority. According to actual needs, the system receives the reference signal in order of priority as follows: temperature signals, infrared signals, light intensity signal.

6 Conclusion

LED lighting system designed in this paper, using C8051F020 microcontroller as a control core to realize the intensity according to ambient light, infrared radiation, temperature changes in the automatic switch, adjust the brightness and other functions, highlighting the advantages of LED energy efficient lighting, and thus has more good practical reference value. The most prominent feature of this system is functional, high integration, set for measurement, control, display as a whole, including light intensity, infrared radiation, the temperature sensor 3. In practice, you can set according to the different needs of the relevant threshold or highlight a feature. For example, applications in the corridor, bathroom lighting, sensing the infrared radiation is used when the main function does not light when no one, it was only when the bright lights, to the effect of saving energy; used in offices, classrooms mainly used when the intensity lighting sensors and dimming function, so that light intensity and stability at a set value, during the day does not light or dark, night lights, to improve energy efficiency; application in the smart table lamp, table lighting, can have the workpiece temperature monitoring (such as when the lamp is off more than 80 ); and so on.

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