The LED electronic screen in traffic is mostly used for trains, which can be divided into two types: one is placed on the outside of the carriage, which is used to display the train operation section, running direction and the name of the current arrival station. It can also display other service information according to the operation needs; Text display can be static, scrolling, translation, waterfall, animation and other effects. The maximum number of displayed characters is 16 × 16, 12 lattice characters. The other is the terminal LED display, which is placed in the train. The terminal station LED display can preset the terminal station according to the train operation requirements, and display the current terminal station in real time. At the same time, it can also display the current temperature in the train. The maximum number of displayed characters is 16 × 16 dot matrix characters.
LED display system screen is composed of single-chip microcomputer control unit and display unit. A single display unit can display four 16 × 16 Chinese characters. If a certain scale LED graphic display system is manufactured, only a number of intelligent display units can be used and the method of “building blocks” can be used. The serial communication is selected between the display units in the system. The control unit not only acts as the control display unit and transmits the instructions and signals of the upper computer, but also has a single bus digital temperature sensor 18B20. Thanks to the module planning of the control circuit, if the humidity measurement is also required, 18B20 can be upgraded to the module circuit composed of Dallas DS2438 and Honeywell hih23610. In order to meet the communication needs of the whole vehicle, the CAN bus communication method is selected between the upper computer and the control units in the vehicle.
The display unit is composed of LED display panel and display circuit. LED display panel is a 16 × 64 dot matrix general intelligent display unit composed of four dot matrix modules. A single display unit can display four 16 × 16 dot matrix Chinese characters or symbols on the full screen. Serial communication is selected between the display units in the system, and then the work of all systems is harmonious. The display circuit consists of two 16 pin parallel ports, two 74h245 tri state bus drivers, one 74hc04d six inverter, two 74h138 eight decoders and eight 74HC595 shift latch. The control circuit center is a high-speed microcontroller 77e58 of Winbond. The crystal frequency is 24 MHz. A t29c020a is a 256 K ROM, which is used to store 16 × 16 dot matrix Chinese character library and 16 × 8 dot matrix ASCII code table. A t24c020 is ep2rom based on I2C serial bus, which stores preset sentences, such as subway station title, greetings, etc. The interior temperature is measured by a single bus digital temperature sensor 18B20. SJA1000 and TJA1040 are can bus controllers and transceivers respectively.