LED display in the subway as a public-facing information display terminal, has a very wide range of residential and commercial value.
Currently running subway cars in the country in general are equipped with a LED display, but additional features small, single-screen display. To cope with the new subway passenger information systems, we have designed a new type of multi-bus LED display dynamic screen.
The display not only in communicating with a variety of external bus interface, the internal control circuit design also uses a single bus and I2C bus devices.
LED screen on the subway in two ways: one is placed on the outside of the car, the train operating range for displaying, running direction of the current station and the station name, in English and is compatible with the display; other services may also need to display information according to the operation; the text display can be choose static, scroll, pan, waterfalls, animation and other effects, the maximum number of characters is 16 × 16 dot matrix display 12 characters. Another is the end of the led street lighting Manufacturer, placed in the car, the train operator terminal LED display can request pre-terminus, and real-time display of the current terminus, while displaying the current temperature inside the car, the maximum number of characters displayed 16 × 16 dot matrix characters for eight.
2 System Components
LED display system screen consists of two single-chip control unit and a display unit, the display unit can display a single 16 × 16 characters 4, if making the production of a certain size LED graphic display system, as long as the number of intelligent display unit, a "building block "approach can be realized using serial communication links between system each display unit. In addition to the control unit is responsible for controlling the display unit and the transmission of instructions and PC signals, but also built a single-bus digital temperature sensor 18B20. Thanks to modular design of the control circuit, if the humidity measurements under the requirements of the situation there, 18b20 can be upgraded to the module's circuit Dallas DS2438 and Honeywell's HIH23610 composition. In order to meet the communication needs of the vehicle, between the control unit using the PC and the car's CAN bus to communicate.
The display unit by the LED display panel and a display circuit of two parts, LED display panel is composed of four modules of the lattice 16 × 64 dot matrix display unit generic smart single full screen display unit may display four 16 × 16 dot matrix characters or symbol, the system uses a serial communication link between the display unit, allowing work to harmonize the entire system. Display circuit consists of two 16-pin ribbon cable port, two 74H245 tristate bus driver, a 74HC04D six inverters, two 74H138 eight decoder and 8 74HC595 shift latch components. The control circuit of the high-speed microcontroller core for WINBOND 77E58, crystal frequency is 24MHz.AT29C020A for 256K of ROM, for storing 16 × 16 dot matrix character base and 16 × 8 dot matrix ASCII code table. AT24C020 is based on the I2C serial bus EP2ROM, storing pre-set statements, such as the subway station names, greetings and so on. 18b20 temperature inside the vehicle is measured by a single bus digital temperature sensor. SJA1000 CAN bus and TJA1040 respectively controller and transceiver.
3.1 Design of the control circuit unit
The whole system winbond dynamic core microcontroller 77E58, 77E58 with a redesigned microprocessor core, the instruction compatible Series 51, but because of the clock cycle is only four cycles, at the same clock frequency, its speed generally higher than traditional 8051 increased by 2 to 3 times, so a good solution to large-capacity dynamic characters displayed on the microcontroller frequency requirements, in addition to its own watchdog. 77E58 74LS373 latch controlled by the flash memory AT29C020, size is 256K. Since the memory capacity of more than 64K, so using a paging addressing methods in the design, which uses flash memory P1.1 and P1.2 to conduct the election page, is divided into four pages addressing size 64K, P1.5 except for external AT29C020 chip select, but also to ensure that the right cause P1.1 and P1.2 AT29C020 on a 16-pin ribbon cable connector multiplexed misuse. CAN controller is a key part of the communication, in order to improve the anti-jamming capability between SJA1000 CAN controller and CAN transceiver TJA1040 plus access high-speed optocoupler 6N137, microcontroller through P3.0 SJA1000 CAN controller chip select. 18B20 single bus device, the device and the microcontroller interface only occupies one I / O ports, the temperature can be directly converted into a digital signal, and 9 digit code serial output mode, the choice in the control circuit P1.4 complete 18B20 chip select and data transmission capabilities. AT24C020 clock line SCL and SDA bidirectional data lines were connected to the microcontroller pins P1.6 and P1.7.16 cable interface control circuit and display interface part of the circuit.
3.2 The display unit connected to the control
Display circuit section through a 16-pin cable (1) 16-pin ribbon cable port and the port connected to the control circuit, the 16-pin cable outlet (1) single-chip instruction and data will be transmitted to the led street light wholesale circuit, the 16-pin cable (2 ) is used to cascade multiple display screens, its wiring and 16-pin cable outlet (1) is basically the same, but pay attention to the R side of the connection from left to right are two of the first eight 74H595 end of DS chart , when it is in cascade (1) connected in series with the port under a 16-pin cable screen (Figure 1). CLK is a clock signal terminal, STR latch side row, R is the data side, G (GND), LOE lit for row enable terminal, A, B, C, D for the row select terminal. The specific role of each port are as follows: A, B, C, D for row selection terminal for controlling specific data from the PC to the specified line on the display panel, R is the data side, the microcontroller accepts data transmission. LED display unit working sequence is as follows: CLK clock signal terminal R side, after receiving a data, by the control circuit to a pulse rise artificially, STR data in a row (16 × 4) 64 transmits data after all, to the rising edge of a pulse to latch data; LOE lit the row set by the microcontroller. Display circuit diagram shown in Figure 3.
No comments:
Post a Comment