Sôn am egwyddorion dylunio sylfaenol sgriniau arddangos dan arweiniad isffordd; mae gan sgriniau arddangos dan arweiniad dan do, fel math o derfynell arddangos gwybodaeth sy'n wynebu'r cyhoedd yn yr isffordd, ystod eang iawn o werthoedd sifil a masnachol.
At present, the subway vehicles operating in the country are generally equipped with indoor LED display screens, but there are fewer additional functions and the screen display content is single. In order to cooperate with the use of the new subway passenger information system, we designed a new multi-bus subway LED display dynamic screen.
Arddangosfa dan arweiniad isffordd
Arddangosfa dan arweiniad dan do isffordd
The display not only has a variety of bus interfaces for external communication, but also uses single bus and I2C bus devices in the design of the internal control circuit.
There are two types of LED screens on the subway: one is placed on the outside of the carriage, used to display the train running section, running direction and the name of the current station, compatible with Chinese and English; it can also display other service information according to the needs of the operation; text display can be Choose static, scrolling, translation, waterfall, animation and other effects, the number of displayed characters is 12 1616 dot matrix characters. The other is the terminal indoor LED display, which is placed in the car. The terminal indoor LED display can preset the terminal according to the train operation requirements and display the current terminal in real time. It can also display the current temperature in the car and display characters. The number is 8 1616 dot matrix characters.
Arddangosfa dan arweiniad isffordd
Arddangosfa dan arweiniad isffordd
System Components
The LED display system screen is composed of a single-chip microcomputer control unit and a display unit. A single display unit can display 4 Chinese characters of 1616. If a certain size LED graphic display system is produced, only a number of intelligent display units are used. The method of "building blocks" can be realized, and the display units in the system are connected by serial communication. In addition to controlling the display unit and transmitting instructions and signals from the upper computer, the control unit also embeds a single-bus digital temperature sensor 18B20. Thanks to the modular design of the control circuit, if humidity measurement is also required, 18b20 can be upgraded to a modular circuit composed of Dallas' DS2438 and HoneywELl's HIH23610. In order to meet the communication needs of the entire vehicle, CAN bus communication is adopted between the host computer and each control unit in the vehicle.
Arddangosfa dan arweiniad dan do isffordd
Arddangosfa dan arweiniad dan do isffordd
hardware design
The display unit is composed of an LED display panel and a display circuit. The LED display unit board is a 1664 dot matrix universal intelligent display unit composed of 4 dot matrix modules. A single display unit can display 4 1616 dot matrix Chinese characters on the full screen. Or symbol, serial communication is adopted between the display units in the system, so that the work of the whole system is coordinated and unified. The display circuit consists of two 16-pin cable ports, two 74H245 three-state bus drivers, one 74HC04D six inverters, two 74H138 eight decoders and eight 74HC595 shift latches. The core of the control circuit is WINBOND's high-speed single-chip microcomputer 77E58, the crystal frequency is 24MHz. AT29C020A is a 256K ROM, used to store 1616 dot matrix Chinese character library and 168 dot matrix ASCII code table. AT24C020 is an EP2ROM based on the I2C serial bus, which stores pre-set sentences, such as subway station names, greetings, etc. The temperature in the vehicle is measured by a single-bus type digital temperature sensor 18b20. SJA1000 and TJA1040 are CAN bus controller and transceiver respectively.
Control circuit unit design
The whole system is based on Winbond's dynamic microcontroller 77E58. 77E58 uses a redesigned microprocessor core. Its instructions are compatible with the 51 series. However, since the clock cycle is only 4 cycles, its operating speed is generally faster than that of the same clock frequency. The traditional 8051 is increased by 23 times, so it solves the frequency requirements of the single-chip microcomputer during the dynamic display of large-capacity Chinese characters. In addition, it also comes with a watchdog. 77E58 controls the flash memory AT29C020 through the latch 74LS373, the size is 256K. Because the memory capacity is greater than 64K, the page addressing method is adopted in the design, that is, use P1.1 and P1.2 to page select the flash memory. It is divided into 4 pages. The addressing size of each page is 64K. In addition to the chip selection of AT29C020, P1.5 also ensures that P1.1 and P1.2 are not caused to AT29C020 when they are multiplexed on the 16-pin cable interface. Misoperation. The CAN controller is the key part of communication. In order to improve the anti-interference ability, a 6N137 high-speed optocoupler is added between the CAN controller SJA1000 and the CAN transceiver TJA1040, and the single-chip microcomputer selects the CAN controller SJA1000 through P3.0. The 18B20 is a single-bus device. The interface between the device and the single-chip microcomputer only needs to occupy one I/O port. It can directly convert the temperature into a digital signal and output it serially in a 9-bit digital code mode. P1.4 is selected in the control circuit to complete the pairing. 18B20 chip selection and data transmission function. The clock line SCL and the bidirectional data line SDA of AT24C020 are respectively connected to the P1.6 and P1.7 of the single-chip microcomputer. The 16-pin cable interface is the interface part of the control circuit and the display circuit.
Display unit connection and control
The display circuit part is connected to the 16-pin cable port of the control circuit part through the 16-pin cable (1) port. The 16-pin cable port (1) transmits the instructions and data of the single-chip microcomputer to the LED display circuit. The 16-pin cable (2) ) Used for the cascading of multiple display screens. Its connection is basically the same as the 16-pin cable port (1), but it should be noted that the R terminal is connected to the 8th 74H595 DS terminal from left to right in Figure 2. When cascading, it will be connected in series with the 16-pin cable (1) port of the next display screen (as shown in Figure 1). CLK is the clock signal terminal, STR is the row latch terminal, R is the data terminal, G (GND) and LOE are the row lighting enable terminals, and A, B, C, and D are the row selection terminals. The specific functions of each port are as follows: A, B, C, D are row selection terminals, which are used to control the data from the host computer to the specified row on the display panel, and R is the data terminal, which accepts the data transmitted by the single-chip microcomputer. The working sequence of the LED display unit is as follows: After the CLK clock signal terminal receives a data at the R terminal, the control circuit artificially gives a rising edge of the pulse. A rising edge of a pulse is used to latch the data; LOE is set by the microcontroller to light the row. The schematic diagram of the display circuit is shown in Figure 3.
Modular design
Metro vehicles have different requirements for indoor LED display screens according to actual conditions, so we have fully considered this when designing the circuit, that is, specific modules can be interchanged under the condition that the main functions and structure remain unchanged. This structure makes the LED control circuit have good scalability and ease of use.
Temperature and humidity module
In the hot and rainy areas of the south, despite the constant temperature air-conditioning in the car, humidity is also an important indicator of concern to passengers. The temperature and humidity module we designed has the function of measuring temperature and humidity. The temperature module and the temperature and humidity module have the same socket interface, and both have a single bus structure, and both are controlled by the P1.4 port, so the exchange is very convenient. HIH3610 is a three-terminal integrated humidity sensor with voltage output produced by Honeywell. DS2438 is a 10-bit A/D converter with a single bus communication interface. The chip contains a high-resolution digital temperature sensor, which can be used for the temperature of the humidity sensor. compensate.
485 bus expansion module
As a mature and cheap bus, the 485 bus has an irreplaceable position in the industrial field and the transportation field. For this reason, we designed the 485 bus expansion module, which can replace the original CAN module for external communication. This module uses MAXIM's photoelectrically isolated MXL1535E as the 485 transceiver. In order to ensure compatibility in control, both MXL1535E and SJA1000 are chip-selected through P3.0. In addition, a transformer provides 2500VRMS electrical isolation between the RS2485 side and the controller or control logic side. A TVS diode circuit is added to the output of the module to reduce line surge interference. Jumpers can also be used to determine whether to load the terminal resistance of the bus.
software design
The system software is composed of upper computer management software and unit controller control software. The upper computer management software is developed on the Windows22000 operating platform using C plus plus BUILD6.0, including display mode selection (including static, flashing, scrolling, typing, etc.), scrolling direction selection (including up and down scrolling and left and right scrolling), Dynamic display speed adjustment (ie text flashing frequency, scroll speed, typing display speed, etc.), display content input and display preview, etc.
When the system is running, the system can not only display characters such as station announcements, advertisements, etc. according to the preset, but also manually input the required display characters. The unit controller control software adopts 8051 KEILC programming, solidified in the EEPROM of the single-chip 77E58, and mainly completes the functions of communication between the upper and lower computers, data acquisition of temperature and humidity, and I/O interface control. In actual operation, the temperature measurement accuracy reaches ±0.5 degree , and the humidity measurement accuracy reaches ±2 percent RH.
in conclusion
From the hardware schematic design, logical structure, composition block diagram, etc., the design ideas of the subway indoor led display are introduced. Through the design of the fieldbus interface module and the temperature and humidity module interface, the indoor led display can adapt to different environments. Requirement, with good scalability and versatility. After many tests, the indoor LED display has been installed in the domestic subway new passenger information system for trial use, and the effect is good. Practice has proved that the display screen can well complete the static display of Chinese characters and graphics and various dynamic displays, and has the characteristics of high brightness, no flicker, and simple logic control, which fully meets the display requirements of subway vehicles on the LED screen.
