Dynamic LED display system

A linear array LED dynamic display system using the persistence of vision effect of the human eye is developed. The system is driven by a motor to rotate a row of LEDs at high speed, and the LED on and off time is accurately controlled by a single-chip microcomputer, so as to realize the display of characters, graphics and simple dynamic pictures. The modeling software is written in Visual Basic 6.0, the content to be displayed is modeled and converted into a digital signal, and the signal is transmitted to the display screen by wireless or wired means. The system consists of three parts: PC-side software, mobile controller, and display screen. It can change the display content and display mode in real time, and can provide a clear display screen within a range of 360.
As a new type of display material, LED dot matrix has developed rapidly in recent years and has a good market prospect. Among them, LED large-screen display screens are widely used in industry, transportation, commercial advertising, news releases, sports competitions, electronic scene simulation and other fields. However, the existing LED large screens require a large number of LEDs and driver chips, and the control is complex, making the display screen expensive and difficult to operate. At present, some domestic research results have the disadvantages of uneven display brightness and inability to display in real time. It is understood that the content to be displayed is usually burned into the chip, and the content is fixed and displayed in a loop. The display content and display mode cannot be changed in real time, which is inconvenient to use and expensive. This article will apply the principle of visual persistence to develop a new type of ring display system. A row of 64-bit LEDs is driven by a motor to rotate at high speed, and the single-chip microcomputer accurately controls the clear display of characters, graphics and simple dynamic pictures, and the display content and display mode can be changed in real time. The system principle is cleverly applied, the technology content is high, the cost is low, and the market prospects are broad, which can become a new economic growth point.

1 Principle

1.1 Persistence of Vision Effect

The persistence of vision effect refers to the light image formed on the human retina by the light emitted or reflected by the scene, which will remain in the human vision for a period of time. Even if the scene disappears from the field of vision, the light image will not disappear immediately. The persistence time is about 0.05 to 0.2 seconds. Experiments show that when the external light source suddenly disappears, the brightness of the human eye gradually decreases according to the exponential law. In this way, when a light source is repeatedly turned on and off, the human eye can detect the change in brightness when the on-off frequency is low; and when the on-off frequency increases, the eye gradually cannot detect the corresponding brightness change. Experiments have shown that the critical flicker frequency is about 24Hz. Therefore, a movie with 24 frames per second looks like a continuous moving image to people. Because vision has persistence, when people repeatedly turn on and off light at a frequency higher than the critical flicker frequency, the subjective brightness perception they get is actually the average of the objective brightness. The persistence of vision effect can be said to be the visual physiological basis for the display of static images and moving images. When the light source is pulsed (with very small intervals), people will feel that it is always shining and has an average brightness.

1.2 Display Basic Principles

This system uses the principle of visual persistence to display characters or images. 64 ultra-high brightness LEDs are arranged in a row, and then the Chinese characters to be displayed are decomposed into 32×32 dot matrix and the graphics are decomposed into 64×64 dot matrix. The data of each column is sent to the LED dot matrix in sequence through the single-chip computer programming. The LED is driven to rotate by the high-speed rotation of the motor, and the content to be displayed is refreshed every circle. In this way, due to the visual persistence effect of the human eye, the display content seen by people is the same as the flat continuous display effect.

2 Hardware System

The hardware system mainly consists of two parts: the mobile controller and the display screen, as shown in Figure 1. The mobile controller is mainly responsible for receiving the PC software to fetch data, adding control characters and saving them, and can also send specific control commands to the display screen, switch display content, and change display effects. The display screen mainly has motor control speed and single-chip microcomputer control E3jLED display content.

2.1 Mobile Controller

The mobile controller is composed of 5 parts: single chip microcomputer AT89C55, serial port transceiver, wireless transmission module, keyboard and LCD display.

The single-chip microcomputer uses AT89C55, which has a large memory capacity; the serial port transceiver uses the mature serial transceiver chip MAX232; the wireless transmission module uses the RFW102 chipset, which is a half-duplex DSSS wireless transceiver IC, using ASK modulation, the operating frequency is 2.4GHz, and the power consumption is very low. This chipset is a short-range wireless transceiver IC with a maximum transmission rate of 1Mb/s; the keyboard control keys are composed of 4 keys, namely "OK", "Exit", "Left Shift", and "Right Shift". Due to the small number of keys, they are directly connected to 4 I/O ports respectively; the LCD screen uses a 128x64 LCD module, which can communicate directly with the CPU. The keyboard and LCD form a powerful remote control menu. Through the 4 keys of "Exit", "OK", "Left Shift", and "Right Shift", powerful functions such as receiving data from the PC, saving data, and wirelessly sending data can be realized.

2.2 Display

The display screen is mainly composed of a single-chip control circuit, a dot matrix consisting of a row of 64 ultra-high brightness LEDs, and a motor.

The single-chip control circuit is mainly composed of 89S8252 single-chip microcomputer, wireless receiving module and several 7415373 latches. The cost-effective AT89S8252 single-chip microcomputer is used as the main controller. It has its own EEPROM and can be used as a display cache, eliminating the conventional external memory expansion, simplifying the peripheral circuit, and compatible with MCS51 instructions. It is a powerful single-chip microcomputer. The circuit is designed with two data receiving methods: wired and wireless. After receiving the data wirelessly, the data is stored in the EEPROM, so that the data will not be lost after power failure. In addition, 8 7415373 are expanded on the bus of the single-chip microcomputer. Each 7415373 controls 8 LEDs, so the single-chip microcomputer can flexibly control the on and off status of 64 LEDs.

The motor part consists of an adjustable speed DC motor, a DC speed regulator, and brushes. The motor uses a speed-adjustable DC motor produced by Panasonic, with a rated working voltage of 220V and an adjustable speed range of 0-6000 r/min. The speed control system adopts the terminal voltage speed control method.

3 Software System

3.1 PC Software

The PC software is programmed with Visual Basic 6.0. It can directly fetch fonts and send data, with a friendly interface and simple operation. The main function is to convert Chinese characters, English, numbers and graphics into data information with certain rules on the PC in real time, and transmit this data to the single-chip microcomputer for processing through the serial port of the PC.

3.1.1 Design ideas

The software uses real-time modeling: data graphics - data. By introducing the intermediate quantity of graphics, the extraction of fonts becomes flexible, and any font or symbol can be converted instantly. The main program flow chart of the PC software is shown in Figure 2.

3.1.2 Character Modulus Process

When the user clicks the text box, the content of the text box is set to empty. After the input is completed, the user presses the modulo button, and the program first determines whether the population is a character or a graphic. If it is determined to be in character mode, the extracted single character is mapped to the picture box. Determine whether the current character is a Chinese character or a non-Chinese character. If it is a Chinese character, a 32x32 dot matrix is ​​used, and if it is English, a number, and a symbol, a 16x32 dot matrix is ​​used. The modulo part uses intersection modulo. After the character is mapped to the picture box, the intersection color is judged, black is judged as 0, and white is judged as 1. The modulo data is output to the output text box. The character extension function is designed for the insufficient precision of the 32×32 dot matrix, and some points cannot be displayed when taking Songti characters. The color is not only taken at 32×32 intersections, but at each intersection and a small range of points centered on the intersection. Once the color of a point in the range is judged to be black, the Boolean value at the intersection is set to 0. Boldface is the default font.

3.1.3 Graphics Modulus Process

When the graphic mode is selected, the character modulo function is set to locked, leaving only the main button of the character function in an active state. Only the graphic box appears on the interface, and the user can draw or load an image. After the input is completed, the user presses the modulo button, and the program first determines whether the entry is a font or a graphic. When it is determined to be a graphic mode, it automatically jumps into the graphic font segment code. The modulo part uses intersection modulo. After the graphic is mapped to the picture frame, the intersection color is judged, black is judged as 0, and white is judged as 1. And the modulo data is output to the output text box.

3.2 Mobile Controller Program

After the program is powered on and initialized, it is in a waiting state. When a serial port interrupt comes, it is processed first. Sending wireless data is controlled by the keyboard and menu. The flow chart of the mobile controller main program is shown in Figure 3; the wireless sending subroutine is shown in Figure 4.

3.3 Display screen program

The single-chip microcomputer controls the LED on and off and the reception of wireless data. After the data is received through the wireless module, the serial interface of the single-chip microcomputer receives the data and transmits it to the main control chip AT89S8252 for processing. When wireless data is transmitted, the received data is processed first. The main program flow chart of the display screen is shown in Figure 5. The wireless data receiving subroutine flow chart is shown in Figure 6. Whether the display screen can clearly display the content is mainly considered from the following aspects: 1) The single-chip microcomputer controls the LED on and off time: T=S/V, S is the LED surface width, and V is the motor rotation linear speed; 2) The axis of the motor is kept balanced when the motor rotates; 3) The contrast of ambient light.

4 Conclusion

This system displays English characters in 16×32 dot matrix, Chinese characters in 32×32 dot matrix, and graphics in 64×64 dot matrix. People can see clear dynamic display content within 360 degrees. The module software written in Visual Basic 6.0 can take modules in time and send data through the COM port. It can input content in real time to realize the touch of character graphics; it can input graphics by handwriting, realize the display of any graphics, and can display simple dynamic pictures. The system adopts Bluetooth-like wireless technology, and the data transmission is stable, accurate, safe and reliable. Both wireless and wired data transmission methods can ensure accurate data transmission. The LED surface width is selected to be 3mm, the distance from the axis to the column dot matrix LED is 160mm, and the full screen can display about 22 Chinese characters. The size of the displayed content is mainly determined by the above conditions and the rotation speed. The system has the characteristics of simple structure, unique viewing angle, novel design, and easy use. It has high social application value and can be widely used in commercial advertisements, conference notices, slogans, environmental decoration, and visual persistence phenomenon demonstration experiments in higher physics teaching.