Progress in research on LED light output structure

1 Introduction

Intelligent lighting systems are widely used in intelligent office buildings and modern buildings, but there are few research applications for teaching buildings, which leads to the widespread use of traditional lighting systems. The basic structure is that power lines are based on equipment control requirements. The split line uses a manual switch to directly control the power supply, and there is no concept of controlling the flow of information. This paper discusses the intelligent lighting system based on CAN/LIN bus, realizes centralized management of the whole system and reduces the management cost of the system. The use of dimmable electronic ballasts for constant illumination control, full use of daylight, truly achieves reasonable energy savings, creating a comfortable learning environment for students; soft start of the lamps, extending the service life and reducing the operating costs of the system.

The Controller Area Network (CAN) is a new generation network communication protocol with open architecture and broadcast. CAN was first introduced for data communication between the internal measurement and execution components of the car. It can work reliably under strong electromagnetic interference environment with low cost and high real-time processing capability [1]. The LIN bus is a low-cost serial communication network that aims to provide accessibility to existing automotive networks such as the CAN bus. The use of the LIN bus can result in significant cost savings in situations where bandwidth and versatility of high-end automotive buses like CAN are not required. In LIN-implemented systems, analog semaphores are typically replaced with digital semaphores, which optimize bus performance. Therefore, the CAN/LIN bus quickly expanded from the original automotive industry to the industrial control field [2].

2, system design

The trunk line of this system adopts CAN bus, and the branch line adopts LIN bus. The CAN bus has high reliability, high speed and long distance transmission, and the development system is cheap. Its unique multi-master transmission mode enables each extension (node) to send data autonomously according to the need, without the host continuously polling, saving network. The data traffic on the high transmission efficiency. The above performance of the CAN bus has been solidified in the CAN bus processing chip, which is extremely convenient to use [3]. The LIN bus is based on a general-purpose UART interface. Almost all microcontrollers have the necessary hardware for LIN. The network uses very few signal lines (a 12V signal bus and a node-synchronous clock line with no fixed time reference), and the hardware cost of the device is low [ 2].

The function realized by the digital tunable electronic ballast intelligent lighting system [4]:

(1) Decentralized control: Distribute control functions to each sub-controller of the system;

(2) Fully automatic dimming: The lighting system works in a fully automatic state. The system can set several states. These states will automatically switch to each other according to the preset time, and the illumination will be automatically adjusted to the optimal working level.

(3) The light-off state of the unit lamp can be observed on each control terminal panel;

(4) Self-locking: If the power is cut off, all the lights will remain off after the call;

(5) Automatic control combined with human intervention, setting switches on site to facilitate operation;

(6) Monitoring and management of the entire lighting system can be realized in the monitoring room;

2.1 Hardware Design [5]
The CAN/LIN bus control system is shown in Figure 1:

Figure 1 CAN / LIN bus control schematic

(1) System unit: PC (with CAN interface card), system power supply, sub-monitoring unit (51 MCU 8LPC902) on each floor, and classroom controller (51 MCU 8LPC902). As the main controller, the PC issues and accepts information to each subunit, monitors the entire lighting system, and is responsible for the logic operation of constant illumination control. The sub-monitoring unit is mainly responsible for communication switching, and adds a CAN/LIN bus gateway to perform data conversion at the interface with the CAN bus.

(2) Input unit: single/double/four-key switch, outdoor/indoor infrared sensor, illuminance sensor, photoelectric sensor, auxiliary input unit, which are used as the signal source of classroom controller, terminal controller on LIN bus The address number is set by the DIP switch, which is mainly responsible for signal acquisition and storage and response bus requirements release information. At the same time, the acquired signal is simply judged to determine the working state of each output unit. The terminal control MCU uses the LIN transceiver to accept the release signal, and the internal signal acquisition adopts the method of cyclic scanning and real-time updating.

(3) Output unit: single/double/four/12-way relay, four/eight-channel dimmer, and four analog output units.

(4) The teaching building corridor is treated as a terminal sub-unit. Using the infrared sensor as an input, the last illuminance calculation value of the main control unit is called to judge, and the illuminance sensor is not separately installed.

2.2 Software Design The control program block diagram of the microcontroller on the LIN bus (shown in Figure 2):