Six common sensors for LED smart lighting


As a device for signal acquisition and electromechanical conversion, the sensor's electromechanical technology has been quite mature. In recent years, sensor technology has made great strides towards miniaturization, intelligence, multi-function and low cost. Various types of sensors, such as photosensitive sensors and infrared sensors, can be combined with LED lighting fixtures to form an intelligent control system. The sensors convert the collected various physical quantity signals into electrical signals, which can be integrated into an AD (analog-to-digital) converter. , MCU (microcontroller), DA (digital-to-analog) converter intelligently processes the collected signals, thereby controlling the turning on and off of LED lighting fixtures. And can set various control requirements on the MCU, control the switching time, brightness, color rendering, colorful change of LED lights, so as to achieve the goal of intelligent lighting control.

Light sensor

The light-sensitive sensor is an ideal electronic sensor that can control the automatic switching of the circuit due to the change in illuminance during daylight and darkness (sunrise, sunset). The photosensitive sensor can automatically control the opening and closing of LED lighting fixtures according to the weather, time period and area. In bright daylight hours, the power consumption is reduced by reducing its output power. Compared with the use of fluorescent lamps, the convenience store with an area of 200 square meters can reduce the power consumption by up to 53%, and the life span is also about 50,000 to 100,000 hours. Under normal circumstances, the life of LED lighting fixtures is about 40,000 hours; the color of the light can also be changed in RGB (red, green, blue) colorful ways to make the lights more colorful and the atmosphere more active.

Infrared sensor

Infrared sensors work by detecting the infrared rays emitted by the human body. The main principle is: the infrared ray of about 10μm emitted by the human body is enhanced by the Fresnel filter lens and collected on the pyroelectric element PIR (passive infrared) detector. When a person moves, the emission position of infrared radiation will change. The element will lose the charge balance, and the pyroelectric effect will release the charge. The infrared sensor will convert the change of infrared radiation energy through the Fresnel filter lens into an electrical signal, that is, thermoelectric conversion. When there is no human body moving in the detection area of the passive infrared detector, the infrared sensor senses only the background temperature. When the human body enters the detection area, through the Fresnel lens, the pyroelectric infrared sensor senses the human body temperature and The difference in background temperature, after the signal is collected, is compared with the existing detection data in the system to determine whether someone or other infrared source has entered the detection area.

The passive infrared sensor has three key components: Fresnel filter lens, pyroelectric infrared sensor and matching low noise amplifier. The Fresnel lens has two functions: one is the focusing effect, that is, the pyroelectric infrared signal is refracted on the PIR; the second is to divide the detection area into several bright and dark areas, so that moving objects/people entering the detection area can In the form of temperature changes, PIR infrared signals are generated on the PIR. It is generally matched with a low-noise amplifier. When the ambient temperature on the detector rises, especially when it approaches the normal human body temperature (37°C), the sensitivity of the sensor decreases, and the gain is compensated through it to increase its sensitivity. The output signal can be used to drive the electronic switch to realize the switch control of the LED lighting circuit.

Ultrasonic sensor

Ultrasonic sensors, which are similar to infrared sensor applications, have gained more applications in automatic detection of moving objects in recent years. Ultrasonic sensors mainly use the Doppler principle to emit high-frequency ultrasonic waves beyond the human body's perception through the crystal oscillator. Generally, 25 to 40 kHz waves are typically selected, and then the control module detects the frequency of the reflected waves. If there are objects moving in the area, the reflection There will be slight fluctuations in the wave frequency, that is, the Doppler effect, to judge the movement of objects in the illuminated area, so as to achieve the purpose of controlling the switch.

The longitudinal oscillation characteristics of ultrasonic waves can propagate in gases, liquids and solids, and their propagation speeds are different; it also has refraction and reflection phenomena, and the propagation frequency is lower in air and the attenuation is faster, while it is attenuated in solids and liquids Smaller and spread farther. Ultrasonic sensors make use of these characteristics of ultrasound. Ultrasonic sensors have the characteristics of large sensitivity range, no blind spots, and no interference from obstacles. They have proved to be the most effective method for detecting the movement of small objects. Therefore, the system composed with LED lamps can sensitively control the switch. Due to the high sensitivity of the ultrasonic sensor, the air vibration, ventilation, heating and cooling system and the surrounding space will cause the ultrasonic sensor to trigger falsely, so the ultrasonic sensor needs to be calibrated in time.

Temperature Sensor

The temperature sensor NTC (negative temperature coefficient) is used extensively as an over-temperature protection for LED lamps. If the LED lamps use high-power LED light sources, they must use multi-wing aluminum radiators. Since the LED lamps used for indoor lighting have very little space, the heat dissipation problem is still one of the biggest technical bottlenecks.

Unsatisfactory heat dissipation of LED lamps will lead to early light decay of LED light sources due to overheating. After the LED lamp is turned on, the heat will also be accumulated in the lamp cap due to the automatic rise of hot air, affecting the life of the power supply. Therefore, when designing LED lamps, an NTC can be placed close to the aluminum radiator near the LED light source to collect the temperature of the lamp in real time. When the temperature of the aluminum radiator of the lamp cup rises, this circuit can be used to automatically reduce the output current of the constant current source. Cool the lamp; when the temperature of the aluminum radiator of the lamp cup rises to the limit setting value, the LED power supply is automatically turned off to realize the over-temperature protection of the lamp. When the temperature decreases, the lamp is automatically turned on again.

Voice control sensor

A voice control sensor (microphone array) composed of a voice control sensor, an audio amplifier, a channel selection circuit, a delay opening circuit, and a thyristor control circuit. Determine whether to start the control circuit based on the result of the sound comparison, and use the regulator to set the original value of the sound control sensor. The sound control sensor continuously compares the external sound intensity with the original value, and when the original value is exceeded, it communicates to the control center "Sound" signal, voice-activated sensors are widely used in corridors and public lighting.

Microwave sensor

The microwave induction sensor is a moving object detector designed using the principle of Doppler effect. It detects whether the position of the object moves in a non-contact manner, and then generates the corresponding switch operation. When someone walks into the induction zone and meets the lighting requirements, the induction switch automatically turns on, the load appliance starts to work, and the delay system is activated. As long as the human body does not leave the induction zone, the load appliance will continue to work. When the human body leaves the sensing area, the sensor starts to calculate the delay. When the delay is over, the sensor switch automatically turns off and the load electrical appliance stops working. Really safe, convenient, intelligent and energy-saving.

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