PWM dimming technology is currently considered the most promising LED dimming technology. When performing pulse width PWM dimming, an additional pulse width adjustment signal source needs to be provided. By changing the duty cycle of the input pulse signal, the gate control signal of the LED driver chip to the power field effect transistor is modulated, thereby achieving the purpose of adjusting the current through the LED. The full name of PWM dimming is Pulse Width Modulation. In this dimming method, the brightness of the backlight is actually fixed. It adjusts the brightness of the screen by controlling the periodic turning on and off of the backlight. , for example, displays 75% brightness, turns on the backlight 75% of the time, and turns off the backlight 25% of the time. Due to the persistence of vision effect of the human eye, the screen will appear to the naked eye to be always on at 75% brightness. But in fact it flashes "on-off-on-off" quickly at 100% brightness! As LED lighting develops in the direction of smart lighting, various communication protocols have begun to become the key to smart lighting control technology. Among them, 2.4G, Bluetooth , wifi, zigBee and other protocols are the most widely used.
one. Definition
ZigBee is a two-way wireless communication technology with low power consumption, low cost, short delay, large network capacity, reliability and security. It mainly uses 2.4gHz communication globally, with a maximum transmission rate of 250kb/s and a transmission distance of 75m. Within 65,000 devices can theoretically be connected. What is the concept? Everyone is familiar with wifi. A wireless router can support about 10 devices. If the number exceeds the limit, some devices will be unable to connect to the Internet and will be disconnected. Zigbee can support up to 100 networks in an area, so Zigbee can accommodate a considerable number of network devices. Largely, the wireless dimming solution currently mainly used especially in foreign countries is zigbee.
2. Principle
ZigBee dimming system uses a distributed wireless telemetry, remote control, and remote communication control system composed of computers, wireless communication data transmission technology, computer intelligent information processing, and energy-saving electrical appliance control technologies to achieve intelligent control of lighting equipment. . It can adjust light brightness, switch control, timing control, scene setting and other functions, and achieve the characteristics of safety, energy saving, comfort and efficiency.
three. The application
zigbee is used by major companies such as Philips , Xiaomi , Google , IKEA and Samsung , and is widely used in industries such as smart homes, industrial automation, smart cities, and smart agriculture. Zigbee is mainly used in environments where there are many terminal devices and a small amount of data needs to be transmitted. Of course, zigbee also has its own shortcomings, that is, it requires an additional gateway to connect and cannot be directly connected with a mobile phone. The other is the communication protocol of zigbee between different manufacturers. It is not consistent. Although it is already the zigbee3.0 era, the zigbee protocol between various manufacturers is still not fully interoperable. This requires the gateway device to support multi-protocol standards to achieve unified UI interaction.
