LED dot matrix display principle and procedure

The LED dot matrix display introduced in this article can be used to display parameters such as safety days, time, temperature, etc. The program of this article is written using the real-time operating system RTOS. It is introduced as follows.

1. Hardware composition and working principle

(1) CPU control board: The principle is shown in Figure 1. ATmega16 is the core. A 4-16 decoder CD4514 is added to drive ULN2003 to complete the row scanning of the LED. The real-time clock is composed of DS1302 and a 3.6V rechargeable battery. The clock can still work when the power is off. J3 is the ISP program download interface, J4 is the program debugging interface, and J8 is the external adjustment button. The parameters can be adjusted manually without a remote control. J5 is an integrated infrared receiver. ATmega16 has a hardware ISP interface that can directly drive the serial shift chip 74HC595.

(2) LED display board: The principle is shown in Figure 2. It is composed of 16 8x8 LED dot matrices and can display 4 Chinese characters at the same time. 8 74HC595s complete the column drive of the display screen. The two circuit boards are connected by a 40-core flat cable. A display buffer area is opened in the internal RAM of the CPU. The CPU control board reads the Chinese character dot matrix code inside the flash and writes it to the display buffer area. Then read the first line of data in the video memory, drive the 74HC595 through the ISP interface, convert the serial data to parallel, and then connect the corresponding line. After displaying for 1ms, take the next line of data and display it for 1ms until the 16th line, completing a scan. Then shift the data in the video memory to the left by one position and scan it again. In this way, all the Chinese characters are moved into the video memory and displayed in turn, thus realizing the shift of Chinese characters from right to left. After all the Chinese characters are moved, the registers of time, temperature and safety days are refreshed once.

2. Basic structure of the program

First, divide the tasks according to their functional independence. They are divided into five tasks: time reading and writing, temperature acquisition, LED scanning and display, date and day adjustment, and adjusted parameter flashing. Secondly, determine the priority of the task. Time reading and writing, temperature acquisition are 8 levels, date and day adjustment and adjusted parameter flashing are 5 levels, and LED scanning and display are 3 levels. The priority of the task can also be changed dynamically during program operation. The main program is as follows:

The RTOS timing operating system is used in the programming. The main difference between this program and the general foreground and background programs is that each task (i.e., subroutine) works in an infinite loop. The user only needs to do some initialization work for the task. As for when to run what task, this tedious matter can be left to the system to do, so as to maximize the utilization of the CPU.

3. Usage

The remote control used is a finished TV remote control. Press the power button, and it will display "adjust year ××××" and the adjusted digit will flash. Press the volume "+" to increase the corresponding digit, and after adding to 9, it will return to 0. Press the channel "+" to change the adjusted digit.

At the same time, the corresponding bit flashes.

Press the power button again, and the screen will display “Adjust month ××”, “Adjust day ××”, “Week ××”, “Adjust time ××”, “Adjust minute ××”, and “Adjust day ××××” in sequence, ending.