Design of digital tube dynamic display based on single chip microcomputer

　　1. Introduction

　　The static display system of digital tubes needs to occupy too many single-chip microcomputer lines, but it can ensure normal brightness. In order to solve the problem of occupying too many lines and wasting hardware resources, researchers have developed a series of digital tube driver chips such as 74HC595, which can realize serial-to-parallel working mode and drive digital tubes to achieve static and dynamic display. However, such a working mode exposes problems such as insufficient real-time performance of the control system, and has certain limitations in its application in some occasions where the system response time requirements are relatively high. In order to solve the above-mentioned drawbacks, this paper proposes a design scheme for a dynamic digital tube display based on a single-chip microcomputer, using the IAP15F2K61S2 series single-chip microcomputer as the control core, and adopting a brand-new software and hardware circuit to realize the dynamic display of the digital tube.

　　2. Control system hardware design

　　2.1 Display appearance design

　　This display uses six common anode digital tubes. According to the usual practice, the six digital tubes are arranged horizontally at the top of the product, as shown in Figure 1. This design can conveniently display the control status of the control system. The 40-pin DIP packaged microcontroller is used below, and all parallel port lines are arranged with pins, which can easily realize the external expansion of the system and enhance the portability of this display.

　　The display housing is made of transparent acrylic material, which can transmit visible light well and firmly fix the circuit board.

　　2.2 Display Control Core

　　The core selection IAP15F2K61S2 MCU is the latest 1T MCU launched by STC in 2013. It is an enhanced version of the conventional 51 MCU. The running speed of this series of MCU is 7-12 times faster than that of the ordinary 51 MCU, which can greatly improve the response speed of the MCU control system and reduce the response time of the system.

　　The IAP15F2K61S2 microcontroller integrates a wealth of practical functional components, simplifies the hardware structure of the minimum system of conventional microcontrollers, eliminates external reset circuits and clock circuits, optimizes pin configuration, and configures five 8-bit (P0, P1, P2, P3, P4) and one 2-bit (P5) general parallel I/O lines.

　　This display configures the lower six bits of the P2 port of the IAP15F2K61S2 microcontroller as the selection control signal of the digital tube, and the P0 port as the display segment code transmission data bus of the digital tube.

　　2.3 Display Control Circuit Design

　　The control circuit of this display includes power supply module, drive module, display module, program download module and other modules. The product circuit schematic is shown in Figure 2.

　　The power module of the monitor adopts two power supply modes.

　　The first way is to power the monitor through a USB to serial port downloader, and the second way is to power it through a 5V DC power adapter. It can also be easily converted into a 220V AC power supply. The power supply of the downloader comes from the USB port of the computer. The current that can be provided to the control system is too small, which affects the normal display brightness of the digital tube. The use of 220V AC power supply also requires the addition of too many power processing circuits. The second way, a 5V DC power adapter, is used to power this monitor, which is convenient for powering the product and can also provide sufficient current.

　　The driver module ensures the normal display of the common anode digital tube. Since the output current of the microcontroller pin is limited, the control of the common end of the common anode digital tube by the P2 port requires the addition of a transistor for driving. This display uses the NPN transistor 9013 to realize the control of the common end of the digital tube.

　　Arrange six digital tubes horizontally in a row, the common end is controlled by a transistor, and the data segment is directly connected to the port line of the microcontroller to form the display module of this display.

　　The IAP15F2K61S2 series MCU program can be downloaded through the two pins RXD (P3.0) and TXD (P3.1) configured by its built-in full-duplex asynchronous serial port (UART). This program download method requires very simple hardware conditions and the operation method of downloading software is very convenient, which is favored by many MCU system developers. This display adopts such a program download method.

　　3. Display control system software design

　　3.1 Display Information Processing

　　The dynamic display is a highly efficient display that controls the display position of the digital tube and the corresponding display characters through asynchronous display. When it is necessary to display certain information on the display, the segment code corresponding to the information must be obtained first and stored in the corresponding array as the data to be displayed. Before sending the display segment code, the common anode common terminal of the corresponding digital tube needs to be set to a high level, and then the display code is sent to the digital tube through the P0 port, and the information required to be displayed by the code will be displayed on the display.

　　The arrangement of the display buffer array information is exactly consistent with the hardware of this product and the functions of the display function, so as to facilitate the data display.

　　3.2 System Software Design

　　This product uses six common anode digital tubes to make this display. The design common anode digital tube display code table is as follows:

　　In order to give full play to the modular programming advantages of C language, the dynamic display sub-function is encapsulated as a common module. The program is as follows:

　　When the display is required to work, the main program only needs to pass the address of the first information unit in the display buffer to the inside of the sub-function through the formal parameter of the sub-function. Through the processing of the sub-function, all the data in the display buffer will be displayed in turn.

　　The display effect of this display is shown in Figure 3.

　　4. Summary

　　The digital tube dynamic display designed in this scheme greatly improves the real-time performance of the system, speeds up the response of the system, has lower power consumption, novel structure and low cost, while ensuring the normal operation of the digital tube and saving wires.