Deciphering the hardware design of the LED display control systemSeptember 23, 2022 2022-09-23 9:51
Deciphering the hardware design of the LED display control system
Deciphering the hardware design of the LED display control system
Various LED display systems make us dazzled, but the hardware of LED display control system has many similarities, such as high-end product full-color LED display, its control system mostly uses ARM, CPLD, PAG and other chips , the cost of full-color screens is relatively high, the technology is relatively complex, and the requirements for the quality of hardware are relatively stricter. The monochrome LED display is not the case. Because the monochrome LED display is mainly used in ordinary facade signs, etc., the hardware requirements for the control system are relatively loose. The following is a breakdown of the hardware design of the LED display control system.
The STC89C52 single-chip microcomputer is a single-chip microcomputer of Hongjing Technology. The single-chip microcomputer is compatible with the 8051 single-chip microcomputer. At the same time, there are many improvements. It is an enhanced 51 single-chip microcomputer. Compared with the original 51 single-chip microcomputer, it has the following advantages:
1. The program written by the single-chip microcomputer cannot be read, so that the confidentiality of the production port is good.
2. Wide voltage, not afraid of power supply jitter.
3. Wide temperature range, -40 to 85 degrees.
4. The I/O port has undergone special treatment and has strong anti-interference ability.
5. The power supply system inside the single-chip microcomputer has undergone special treatment.
6. The reset circuit inside the single-chip microcomputer is specially handled, and an external reset circuit is not required.
7. The internal watchdog of the single-chip microcomputer is specially handled, so that the program is not afraid of running away.
8. Optional 6 clock cycles/per machine cycle working mode to improve working speed.
9. The oscillation gain can be reduced to 1/2 of the original.
10. In system programming, expensive emulators and programmers are no longer needed.
11. With P4 port, the number of IO is increased.
12. The speed is fast, the crystal frequency can reach 80M, if you use 6 times faster, the frequency is equivalent to 160M of the ordinary 8051. It is more convenient to use. The specific usage method can be found in its data sheet.
SST39SF040 is a FLASH chip with a capacity of 512K×8, which has 100,000 erasing cycles and 100-year data retention time. It has a small capacity page of 4K per page, which can be page erased and chip erased, which is more convenient to use. See its data sheet for specific usage.
STC62WV256 has a wide range of operating voltage and data capacity of 32K × 8, and its use method is the same as that of general RAM. See its data sheet for details.
Communication part: As the communication of an LED display control system, there should be two independent communication ports, namely two serial ports. And the single-chip microcomputer I chose has only one serial port, which requires one serial port to be used as two serial ports, which will bring about the problem of task competition and assignment. In this design, a hardware switch is set externally to send two serial ports. One external task switch, one is used to receive the data communication of the external computer. One for sending data to an external display. The hardware switch uses the 74HC125 chip. The 74HC125 is a three-state output high-effective four-bus buffer gate. The design is shown in U6 in this schematic diagram. Communication with an external computer requires level conversion. In this design, based on the low-cost design principle, 232 chips are used, but triodes are used for level conversion, which can save more than 4 yuan in cost. The design principle is shown in the Q1 and Q2 parts in the figure.
LED display output part: This part is mainly responsible for perfectly sending the data sent from the serial port to the LED display screen. The data sent from a serial port needs to be sent to each line of the display screen, which requires a corresponding decoding control circuit to In general, this part of the circuit is completed in two parts. In the control part, only the data line and the clock line are separated. Each separation of a pair of data lines and clock lines can control 16 lines of display code on the display. And the circuit part that controls the control line of each row is put into the display screen to do. So here we mainly introduce the control part of the control system. A pair of data comes out from the single-chip microcomputer and then is divided into 8 pairs of data lines and control lines through 4 pieces of 74HC125, so that the control system can control the display screen with a height of 16×8. The decoding lines of the 16th row on the page only need to lead out 4 lines from the control system. After these 4 lines are connected to the display screen, they will be converted into 16-to-1 line control lines by the decoding circuit. The data latch line and the display enable line are also led out to the display screen. With these control lines and data, the display of the entire LED display can be controlled. And this control system can control the LED display screen with 16×8 height and 1024 dots width. This part of the circuit is shown in U5, U7, U8, U9, U10 in the schematic diagram.
Storage part: The storage part is divided into two parts, one part is used for the storage of the display code of the LED display screen, and the other part is used for the storage of the temporary display code. The display code memory adopts SST39SF040, which is a FLASH chip, and the data will not be lost after power failure. According to a Chinese character 32 bytes, the system can store 16384 Chinese characters. The temporary display code memory adopts STC62C256 memory, which is a RAM chip, and the data is lost after power failure, and is used to save the data displayed at that time. This part of the circuit is shown in the U2, U3, U4 parts in the schematic diagram.
The control system also adds a clock chip, which can be used in places with time display requirements.
All the chips used above are SMD packages to reduce the area of the circuit board and reduce the cost of hardware design.
Because the cost is considered everywhere, this control system does not have the hardware lineup of the general system. However, although the product is small and complete, the control system can also complete the task of LED display control.
The hard design of the LED display control system is also derived from the environmental requirements of the product use environment. The full-color LED display is mostly used outdoors, and the outdoor environment needs to face harsh conditions such as wind, sun, rain or snow. Such an outdoor use environment makes the hardware design of the full-color LED display control system relatively strict. , LED display control system hardware design is also in accordance with the needs of the market.