Five common sensors for LED smart lighting

Cecelia Qiu Cecelia Qiu 29 December 2021
Five common sensors for LED smart lighting

As one of the equipment of signal acquisition and electromechanical conversion, the electromechanical technology of sensing technology has been quite mature. In recent years, it has entered the development stage of miniaturization, intelligence, multi-function, and low cost. Various types of sensors, such as photosensitive sensors and infrared sensors, can form an intelligent control system with LED lighting fixtures. The sensors convert various collected physical signals into electrical signals and pass the integrated AD (analog-to-digital) converter , Single-chip microcomputer (microcontroller), DA (digital-to-analog converter), to realize the intelligent processing of the collected signals, so as to control the switch quantity of the LED lighting lamps. And by this, various control requirements can be set on the MCU to control the switching time, brightness, color rendering, and color changes of the LED lights, so as to achieve the purpose of intelligent lighting control.

Five common sensors for LED smart lighting

Light sensor

The photosensitive sensor is an ideal electronic sensor that can control the automatic switch of the circuit due to the change of the illuminance at dawn and dark (sunrise, sunset). The photosensitive sensor can automatically control the opening and closing of the LED lighting fixtures according to the weather, time period and region. During the bright day, the power consumption can be reduced by reducing its output power. Compared with the use of fluorescent lights, a convenience store with an area of ​​200 square meters can reduce power consumption by up to 53%, and its life span is 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 and blue) colorful ways to make the light more colorful and the atmosphere more active.

The photosensitive sensor is an ideal electronic sensor that can control the automatic switch of the circuit due to the change of the illuminance at dawn and dark (sunrise, sunset). The photosensitive sensor can automatically control the opening and closing of the LED lighting fixtures according to the weather, time period and region. In bright daylight, power consumption can be reduced by reducing its output power. Compared with the use of fluorescent lights, a convenience store with an area of ​​200 square meters can reduce power consumption by up to 53%, and its life span is 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 and blue) colorful ways to make the light more colorful and the atmosphere more active.

Infrared sensor

The infrared sensor works by detecting infrared rays emitted by the human body. The main principle is: the infrared radiation 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 the human moves, the position of the infrared radiation will change. The component will lose the charge balance, and a pyroelectric effect will occur to release the charge outward. The infrared sensor converts the change in the infrared radiation energy passing 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, the pyroelectric infrared sensor detects the human body temperature and the temperature through the Fresnel lens. For the difference in background temperature, the signal is collected and compared with the existing detection data in the system to determine whether someone is actually waiting for the infrared source to enter the detection area.

Passive infrared sensors have three key components: Fresnel filter lens, pyroelectric infrared sensor and matching low noise amplifier. The Fresnel lens has two functions: one is focusing, that is, the pyro-infrared signal is refracted on the PIR; the second is to divide the detection area into a number of bright and dark areas, so that moving objects/people entering the detection area can be In the form of temperature changes, a changing pyro-infrared signal is generated on the PIR. Generally, a low-noise amplifier is also matched. When the ambient temperature on the detector rises, especially when it is close to the normal body temperature of the human body (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 similar to infrared sensors have been used in automatic detection of moving objects in recent years. Ultrasonic sensors mainly use the Doppler principle to emit high-frequency ultrasonic waves that exceed the human body's perception through the crystal oscillator. Generally, 25-40kHz waves are typically selected, and then the control module detects the frequency of the reflected waves. If there is movement in the area, the reflection The wave frequency will have a slight fluctuation, that is, the Doppler effect, which can be used to judge the movement of the object 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, the propagation frequency in the air is lower, and the attenuation is faster, but in solids and liquids, it attenuates Smaller, spread farther. Ultrasonic sensors use these characteristics of ultrasound. Ultrasonic sensors have the characteristics of large sensitive range, no blind spots, and no obstacles. They have been proved to be the most effective method for detecting the movement of small objects. Therefore, the system with LED lamps can control the switch sensitively. Due to the high sensitivity of the ultrasonic sensor, air vibration, the movement of the ventilation heating and cooling system and the surrounding space will cause the ultrasonic sensor to generate false triggers, so the ultrasonic sensor needs to be calibrated in time.

Temperature Sensor

The temperature sensor NTC (negative temperature coefficient) as the over-temperature protection of LED lamps has been widely used earlier. If LED lamps use high-power LED light sources, they must use multi-wing aluminum radiators. As LED lamps for indoor lighting have a small space, heat dissipation is still one of the biggest technical bottlenecks.

If the heat dissipation of the LED lamp is not good, it will cause the LED light source to overheat and cause early light decay. After the LED lamp is turned on, the heat will also be enriched in the lamp cap due to the automatic rise of hot air, which affects the life of the power supply. Therefore, when designing LED lamps, an NTC can be attached to the aluminum radiator close to 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 set value, the LED power supply is automatically turned off to realize the lamp over-temperature protection. When the temperature drops, the lamp is automatically turned on again.

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. The sound comparison result is used to determine whether to start the control circuit, and the original value setting of the sound control sensor is given by the regulator. The sound control sensor constantly compares the intensity of the external sound with the original value, and when the original value exceeds the original value, it will convey to the control center that there is "yes". "Sound" signal, voice-activated sensors are widely used in corridors and public lighting places.

Microwave sensor

A microwave induction moving target detector designed with the principle of Doppler effect. This method is to detect whether the position of the object is moved by non-contact, so as to realize the corresponding switch operation. After a person enters the induction zone, when the lighting requirements are met, the induction switch is automatically turned on, and the load appliance starts to work, delaying the start of the system. As long as the person does not leave the induction zone, the load appliance will continue to work. After the person leaves the sensor area, the sensor starts to calculate the delay, the delay is over, the sensor switch is automatically turned off, and the load appliance stops working. Truly safe, convenient, intelligent and energy-saving.

(Summarized by Easybom)

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