1 Introduction
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 size. Incandescent lamps, halogen lamps have a luminous efficiency of 12 to 24 lm / W, fluorescent lamps of 50 to 70 lm / W, and sodium lamps of 90 to 140 lm / W, and most of the power consumption becomes heat. The LED can reach 50 ~ 200lm / W, and the single light has good monochromaticity, narrow spectrum, no filtering, and can directly emit colored visible light. 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, while the power of each LED is only 8 watts. LEDs have an average life of 100,000 hours, 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 sourcesâ€.
2 Intelligent lighting control scheme design
Overall 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 consists of three main components: the sensor part, the controller part and the LED drive circuit and lighting system, see Figure 1.
Figure 1 Block diagram of the lighting control scheme
3 system hardware design
3. 1 sensor section
3. 1. 1 Passive pyroelectric infrared detector
The detector has three key components: Fresnel filter wafer, which passes the filter chip with a cut-off wavelength of 8 ~ 12μm, acts as a band-pass filter, so that the environmental interference is obviously 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 zones and dark zones, so that the moving objects 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 produce a varying electrical signal; the pyroelectric infrared sensor converts the change in infrared radiation energy through the filtered optical chip into an electrical signal , that is, thermoelectric conversion.
The human body has a constant body temperature, usually 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* to 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 voltage, and when there is no one, it is low level. 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. The photoresistor uses a photoelectric effect of a semiconductor to produce a resistor whose resistance value changes with the intensity of the incident light; the incident light intensity, the resistance is small, the incident light is weak, and the resistance is increased. Photoresistors are commonly used for light measurement, light control, and photoelectric conversion (converting changes in light into electrical changes), as shown in Figure 2.
Figure 2 Relationship between photo resistance value and light intensity