LED光带型交通诱导屏的设计

Design of LED Light Ribbon Traffic Guiding Panel

LED光带交通诱导屏是近年来出现的一类新型交通诱导屏。它由静态文字、图形路段标识区和镶嵌其中的LED光带组成,以图形方式呈现道路整体轮廓和走向。LED光带可显示红、绿、黄三色,以之标示路段堵塞、畅通和拥挤三种路况信息。光带诱导屏控制部分由1台工控机和多台光带显示控制器构成,采用RS-485总线按自订通信协议以主从方式进行半双工通信。本文重点阐述了光带显示控制器的设计与实现。光带显示控制器主要由单片机、CPLD和RAM构成。单片机的主要作用是通信处理并生成显示数据。对信源实施游程长度压缩编码保证了LED光带的及时更新。CPLD可实现光带逐色灰度显示。单片机与CPLD共用外部RAM,采用中断和软件定时策略解决了访问冲突问题。为简化印制版布线,提出了CPLD辅助单片机访问外部RAM的方案,采用16bit恒流驱动芯片MBI5027,其断开故障检测功能使系统无需检测电路,仅用软件就可实现LED检测。

As a new traffic guiding panel, LED light ribbon traffic guiding panel appears in recent years. On the panel, static text and route segment are shown to indicate outline and direction of roads. Traffic condition of roads, such as block, smooth and congestion are expressed by different LED colors： red, green and yellow. Control system of panel consists of an industry computer and many LED light rib- bon display controllers, which all connect to RS-485 bus. The system adopts half-duplex mode and self-defined communication protocol. This paper chiefly presents design and implementation for light ribbon display controller. Each controller mainly composes of MCU, CPLD and RAM. MCU per- forms the task of producing display data and dealing with communication, CPLD accomplishes gray display that same color has same gray. Run length compress code is employed to ensure refreshing LED light ribbon quickly. Visiting conflict that MCU and CPLD visit the same RAM in same time can be avoided by applying interruption and software timing strategy. A method which MCU visits RAM assisting by CPLD leads to simplifying PCB wire arrangement. 16 bit constant current driver MBI5027 with function of LED open circuit error detecting makes LED detecting carry out only by software without circuit.