Industry news

2016August

Design scheme of intelligent control system for LED street lamp

From: www.szbako.com Data:10/08/2016

in recent years, with the rapid development of economy and the gradual popularization of cars, the city's traffic problems have attracted more and more attention, the importance of urban road lighting is also increasing. At present, the street lamp lighting in most cities of our country are using & quot; all night light constant illumination & quot; way, control is still simple light control and time control and other traditional methods, which greatly increased the city's electricity consumption. To this end, the government undertakes the huge expenditure, and the service life of the LED street lamp lighting equipment is also greatly reduced. Therefore, the introduction of intelligent transportation system (ITS) has become an important way to improve the level of urban traffic management.

the design with the low power consumption MSP430 SCM main control unit, the pyroelectric infrared signal emitted by the electric infrared sensors to detect human and vehicle, the use of photosensitive resistance measurement of background light intensity, through a constant current source to control LED light intensity. According to the varied time of each season of dark set their own street lights turn on and off time, in a specified time of moving objects were detected realizing the intelligent control of street lamp, to improve the effectiveness of the street lamp, to avoid the waste of power resources.

1 pyroelectric infrared sensor and Fresnel lens


using infrared sensor can detect the infrared light emitted by objects, which can detect the existence of different objects. Manufacturing heat release pyroelectric infrared sensor materials, oxide ceramics and piezoelectric most used, this kind of material has strong spontaneous polarization performance, when subject to thermal radiation arising from changes in temperature dielectric polarization state changed. Because the internal charge is much faster than the change of the surface charge, the two ends of the crystal will have an equal and opposite independent charge, which is the pyroelectric effect of the dielectric. Pyroelectric infrared sensor is to detect the change of temperature of the sensitive element by the heat radiation of the object being measured. Pyroelectric infrared sensor is widely used in security monitoring, electronic anti-theft, automatic control lighting and industrial automatic control and other fields. The infrared energy released by the

object is very weak, and the sensitivity is relatively low when the infrared sensor is used to receive the infrared directly, and it is difficult to meet the system requirements in general. In order to improve the heat release electric infrared sensor receiving sensitivity, on the surface cover a piece of Fresnel lens, the detection distance can be increased to the original 5 to 7 times. Fresnel lens [1] is a made of polyethylene materials according to the Fresnel principle is made of thin plastic lines lens and infrared transmittance was more than 65%. According to the working principle of the Fresnel lens is knowable, when there are moving objects emit infrared into the detection range of the lens, Fresnel lens will produce an alternating & quot; blind & quot; and & quot; high sensitive area & quot; pyroelectric infrared sensor and two reverse series of sensitive element turns to detect moving objects, forming a series of light pulses into the sensors. Therefore, pyroelectric infrared sensor can not detect static objects. The distance between the Fresnel lens and the pyroelectric infrared sensor should be satisfied with the focal length of the Fresnel lens.

2 control system hardware design


hardware for control system based on MSP430 as the core controller, supplemented by external circuit such as AD /DA data acquisition processing system module, a heat release electric infrared sensor module, background light detection module and the LED driving module and. The hardware block diagram of the system is shown in figure 1.



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2.1 data acquisition module

2.1.1 object location detection


signal using passive double element pyroelectric infrared sensor P2288, and on the surface cover a Fresnel lens is used to improve the detection sensitivity. It detects the weak infrared energy emitted by the human body and the vehicle in the form of non contact and transforms it into electrical signal output, and the object location detection circuit is shown in Figure 2. When P2288 detects a person or vehicle entering the detection area, the P2288 generates an alternating infrared radiation signal, and outputs a weak voltage signal (TTL level). And and between the cut-off high output, low level output below the cut-off conduction high output (Uref2 and (used to, used to



signal through the second stage operational amplifier input to the double limit comparator, which RW3 adjusting the second stage operational amplifier magnification rw4 set a threshold level Uref1 U7 U8,) when the detection voltage is greater than the Uref1, U7 of electric flat, U8 output low level, D2 and D3, heat release electric out for high level; when the voltage detected Uref2 U7 U8, level, D2 and D3 conduction, heat release electric out for high level; when the voltage detected Uref1 Uref2 D2 D3 deadline heat release electric out low level. After amplification and shaping the signal input to the microcontroller. The background of

2.1.2 light detection

photosensitive resistor is made of the semiconductor photoelectric effect of a resistance value varies with the changes in the intensity of the incident light resistor and the incident light intensity resistance is reduced. The background light detection circuit is shown in Figure 3 (left), and the collector output voltage of the transistor is input to the A/D converter. Because the microcontroller has been integrated with the high precision of the 12 bit a /D digital to analog converter, so the selection of the internal A /D converter, the analog input range of control in the range of 0 ~ 5V, by the SCM storage and control register Sref determined.



when background light intensity strong time sensitive resistance is reduced, the triode in non working state, transistor collector output low level; when the background light intensity is weak when the photosensitive resistance increases, triode in working condition, transistor collector output high level. When the output is higher than the set value, the object location detection subsystem is opened.

and, in order to avoid due to other reasons (such as lightning, light source, etc.) caused by the influence of, set up Street opened to determine the time is 30s, after 30 seconds of the MCU detects the transistor collector output is indeed higher than the preset value, the SCM sends out object detection signal to open. LED

2.2 constant current source drive module and PWM drive mode


LED because of long life, energy saving, environmental protection and high photoelectric efficiency of many advantages, has become the focus of attention in the field of lighting. According to LED volt ampere characteristic curve can be seen, very steep positive volt ampere characteristics of LED, small driving voltage fluctuation can lead to drastic changes in the LED drive current, which will directly affect the LED's life, luminous flux and reliability. LED unique electrical characteristics makes the LED driver circuit is also facing a greater challenge, LED driver circuit is related to the reliability of the entire LED lighting system performance. So in order to prevent the damage of LED, the design of the drive can be precisely controlled LED drive current. The system design of the constant current source is in the constant voltage mode control increase a current series negative feedback, constant current source output value also reflects the size of the output voltage source, but the precise control of the LED drive current, thereby stabilizing control LED brightness. Constant current source drive circuit is shown in Figure 3 (right). Current series negative feedback is composed of U4 and Q3.

system uses PWM to adjust the brightness of LED light. PWM is used to adjust the LED is actually a fixed DC voltage through a certain frequency to open and close the switch, thereby changing the voltage on the LED. Assuming a fixed DC voltage to provide the maximum current for IMAX, the switching frequency is f and closed cycle T, through the average LED current I is:


so as long as the change in the closed period T can change through the average LED current, and then change the LED brightness. Proportion of assuming that the PWM output system air ratio is τ and the frequency and the output voltage of the PWM respectively for F and upwm, by the circuit of Figure 3 shows the current through the LED value:


, t0=Tτ and I is the value of the instantaneous current and upwm for the output voltage of the PWM. In small current values at the same brightness pulse current drive driven than DC current required, therefore the pulse current drive can bring to the system efficiency.

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3 software system design

according to the hardware design of the function of each module and, system software design is mainly combined with hardware circuit. The system function is divided into control module with independent sub function.

design uses a modular approach to be more easy to read and understand, the software structure is more clear, but also conducive to software debugging. System software programs mainly by the initialization process, the background light detection procedures, the human body infrared signal detection procedures and the RS-485 protocol, such as [6]. After the circuit is started, the single chip microcomputer is initialized and the circuit control system is in the working state. The working flow chart of the system is shown in Figure 4.

in the provisions of the lighting time, if the background light intensity is weak, the host computer is transmitted to the lower computer to work orders and information, otherwise the lower position machine waiting in response to a PC to send commands. Slave response. When a person or vehicle into the infrared detection region SCM according to the intensity of the background light and output PWM signal, driving controller with the LED lighting to ensure the LED light intensity is sufficient to meet the requirements of pavement's visibility. If the lower machine does not detect the infrared signal, the street lamp LED goes out.


4 system flow chart


4 experimental results and analysis

because arrived at the scene to carry out experiment has certain difficulty, so simulation experiments only on the human body infrared signal were detected. System provides for setting the lighting time for PM 6:00~7:00 will heat release electric infrared sensor fixed on the lab bench, the output end of the sensor connected on an oscilloscope probe, to sensor detection area and observe the output waveform oscilloscope. Test results shown in Table 1, A said the sensor did not cover the output of the Fresnel lens; B said the output of the sensor cover Fresnel lens. The results show that the system can accurately control the turn-on time of intelligent street lamp; Fresnel lens can significantly improve the detection sensitivity of the sensor.

Table 1 sensor output results


test constant current source drive circuit choose 1 W of high power LED lamp, through the regulation of PWM for empty ratio detection through the LED current value. If the LED light dark frequency exceeds 100Hz, the human eye to see is the average brightness, rather than the LED flicker. The frequency of the PWM output signal is 1kHz, and the simulation results are shown in Table 2. From table 2, the error precision of the constant current source is proportional to the duty ratio of ±, 4mA, LED, and PWM output signal. The constant current source drive circuit is simple, but its performance is very excellent.
Table 2 LED street lamp operating current test


5 conclusion

research and design intelligent,

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