Design of ambient light measurement and timing circuit for intelligent lighting control

　　Outdoor lighting is usually controlled by manually operated mechanical switches to turn the lighting system on or off. To save energy, you may not want to keep the lighting system on in a certain area all night. In this case, it will be more convenient if the lighting system can be accurately controlled to automatically turn it on or off when necessary. The controller can detect the ambient light intensity, turn on the lights when it gets dark and keep them on for a certain time interval, and then automatically turn them off at a specified time. In the morning, the process is reversed. If the ambient light intensity is still below the preset lighting threshold within the predetermined time, the system will turn on the lights. When the ambient light is bright enough, the system will turn off the lights. It is not difficult to design an intelligent lighting controller based on the ambient light sensor (ALS) to detect and measure the ambient light intensity. Since the controller is equipped with a real-time clock (RTC), it can also turn the lighting system on or off at a specified time. The management system described in this article can be used for mains lighting systems.

　　Integrated system components

　　The lighting controller in this design uses an ALS to measure the ambient light level. There are two different ALSs on the market: one that outputs an analog voltage proportional to the ambient light level and the other that provides a digital output. This system uses a digital output ALS. The controller needs to know the exact time, so a real-time clock (RTC) is used. Considering the possibility of power outages, the time information needs to be backed up by a battery. The time and other parameters are set through the user interface. The user interface here includes two 7-segment LED displays and a button. When the button is pressed briefly, the system displays the time and other parameters; when the button is pressed for a long time, the time and parameters can be adjusted. The system has an automatic/manual switch to enable manual control of the lights. The system is powered by the mains, and the lighting system is connected/disconnected by a relay. The system's digital signals are electrically isolated from the mains.

　　In manual mode, the Auto/Manual switch must be switched to the Manual position. In Manual mode, the relay remains on and the lighting system is turned on/off by a standard wall control switch. When the Manual/Auto switch is in Auto mode, the wall control switch must be on for the controller to work properly. If the wall switch is not on, the controller will not control the lighting. The lighting system may consist of multiple lamps.

　　

　　Figure 3 System schematic diagram

　　With modern semiconductor technology, the system can measure the ambient light level and control the lighting system to turn on/off in a preset manner. This article describes how to design a controller solution that can achieve intelligent lighting management based on ambient light and time information. The system is ideal for mains lighting systems.