The system is developed by using a linear array LED dynamic display system which utilizes the human eye vision effect.The system is driven by a high-speed rotation of the LED by the motor, and the bright time of the LED is precisely controlled by the single chip microcomputer to realize the display of characters, graphics and simple dynamic picture. Using Visual Basic 6.0 to write the mold software, the content to be displayed into a digital signal conversion, and the signal is transmitted to the display wireless or cable. The system consists of PC-side software, mobile controller, display 3 parts, can change the display content and display mode in real time. Range to provide a clear display.
LED dot matrix as a new type of display material, in recent years, rapid development, good market prospects. LED large screen display is widely used in industrial, transportation, commercial advertising, press releases, sports competitions, electronic scene simulation, etc. But the existing LED large screen, requires a large number of LED and driver chip, and control complex , Making the display expensive, easy to operate. At present there are some domestic research results show uneven brightness, can not display real-time shortcomings. It is understood that the content is usually to be recorded into the chip, the contents of the fixed cycle display, can not real-time changes in display content and display, inconvenient to use, and expensive. This paper will use the principle of visual retention, developed a New ring display system. Through the motor to drive a 64-bit LED high-speed rotation, precise control by the microcontroller to achieve the characters, graphics and simple dynamic picture of the clear display, real-time changes in display content and display. System principle application clever, high technological content, low cost, broad market prospects , Can become a new economic growth point.
1 principle
1.1 visual retention effect
The visual persistence effect refers to the light emitted or reflected by the scene, and the light image formed on the human retina is retained for a period of time in human vision, and even if the scene disappears from the field of view, the resulting light does not immediately disappear The residence time is about 0.05 ~ 0.2s. Experiments show that when the external light suddenly disappeared, the brightness of the human eye is gradually reduced by the exponential law. So that when a light source repeatedly off, in the low breaking frequency, the human eye can be found in the brightness of the change; and on-off frequency increases, the eyes can not gradually find the corresponding brightness changes. The experimental results show that the critical flicker frequency is about 24 Hz. So the use of 24 hours per second picture of the film, in people who seem to be a continuous activity of the image. Because the vision is temporary, the subjective brightness sensation is actually the average of the objective brightness when the light is repeatedly turned on and off at the critical flicker frequency. The visual persistence effect can be said to be the visual physiological basis of the static image and the moving image display.When the light source is pulsed (when the interval is small), the person will feel that it is always glowing and is the average brightness.
1.2 shows the basic principles
The system is the use of visual retention principle to achieve the character or image display. The 64 ultra-high brightness LED side by side, and then will display the Chinese characters into 32 × 32 dot matrix, graphics decomposition of 64 × 64 dot matrix, through the single-chip programming to each column of data in order To the LED dot matrix, through the high-speed rotation of the motor drive LED rotation, each circle to re-refresh the content to be displayed, so that the visual effect of the human eye, people see the display content with the same effect of continuous display The
2 hardware system
Hardware system mainly has a mobile controller and display two parts, as shown in Figure 1. Mobile controller is mainly responsible for receiving PC-side software to take touch data, add control characters and save, but also to the display to send a specific control commands, switch display content, change the display. The display is mainly motor control speed and single-chip control E3jLED display content.
2.1 mobile controller
The mobile controller is composed of five parts: single chip AT89C55, serial port transceiver, wireless transmission module, keyboard, liquid crystal display.
Single-chip selection of AT89C55, a large amount of memory; serial port transceiver, the use of mature serial transceiver chip MAX232 composition; wireless transmission module, using RFW102 chipset, which is a half-duplex DSSS wireless transceiver dual use Ic, ASK modulation mode, the operating frequency is 2.4GHz, power consumption is very low. The chipset is short-range wireless transceiver Ic, the maximum transfer rate of 1Mb / s; keyboard control key consists of four keys, namely "OK", " , "Left shift", "right shift", due to fewer keys, so were directly connected to the four I / O port; LCD screen, use 128x64 LCD module, can communicate directly with the CPU. Powerful remote control menu. Through the "exit", "OK", "left", "right" 4 keys to achieve from the PC to accept data, save data, wireless data transmission and other powerful features.
2.2 display
Display mainly by the single-chip control circuit, a 64-bit ultra-high brightness LED composed of column lattice, motor 3 parts.
SCM control circuit mainly by the 89S8252 microcontroller, wireless receiver module and a number of 7415373 latch components. Using the cost-effective AT89S8252 microcontroller as the main controller, it comes with EEPROM, can be used as a display cache, eliminating the need for conventional external memory expansion, simplify the external circuit, compatible MCS51 instruction, is a powerful single-chip. Circuit design of wired and wireless two receive data, wireless way to receive data, the data stored in the EEPROM, so that power will not lose data. Also in the single-chip bus on the expansion of the 8 7415373, each 7415373 control 8 LED, so the microcontroller can be flexible control of 64 LED light off state.
Motor part by the adjustable speed DC motor, DC governor, brush composition. The motor chooses Panasonic to produce a speed adjustable DC motor, its rated working voltage is 220V, adjustable speed range is 0 ~ 6000 r / min. Speed control system uses the terminal voltage control method.
3 software system
3.1 PC software
PC software using Visual Basic 6.0 programming. Can directly take the font, send data, user-friendly, easy to operate. The main function is real-time conversion of Chinese characters, English, numbers and graphics on the PC into certain rules of data information, and this data through the Pc machine's serial port to the microcontroller processing.
3.1.1 design ideas
The software takes the real-time mode: the data graph - the data. By introducing the middle of the graphics, making the extraction of the font becomes flexible, regardless of any fonts, symbols, can achieve real-time conversion.
3.1.2 character mode
The contents of the text box are set to null when the user clicks the text box. To be entered, the user presses the modifier button, the program first determines whether the population is a character or a graphic. If the character mode is determined, the individual characters to be taken are mapped to the picture frame. To determine whether the current characters are Chinese characters or non-Chinese characters, Chinese characters are 32x32 dot matrix, is the English, digital, and symbols are used 16x32 dot matrix. The pattern is mapped to the picture frame, the intersection point color judgment, the black judgment is 0, the white judgment is 1. The output data is output to the output text box. Character extension function is for 32 × 32 dot matrix accuracy is not enough to take some of the words when the song is not shown, color is not only 32 × 32 intersection, but each intersection and the intersection as the center of a small The value of the point in the range of a certain point of color is judged to be black, the intersection of the Boolean value is set to 0. Boldface is the default font.
3.1.3 graphics mold process
When the graphic mode is selected, the character mode function is set to lock, leaving only the character function. The main button is activated. Only the graphic box appears on the interface. The user can draw or load the image. To be entered, the user presses the modifier button, the program first determines whether the entry for the font or graphics. When the graphics mode is determined, it automatically jumps into the graphics word module code. Take the mold part of the use of the intersection point to take the graphics map to the picture box, the intersection of color to determine the black sentenced to 0, white sentenced to 1. And output the modulo data to the output text box.
3.2 Move the controller program
After the program is initialized, it is in a wait state. When the serial port is interrupted, the serial interrupt is prioritized. The transmitted wireless data is controlled by the keyboard and menu.
3.3 Display program
By the single-chip control of the LED off and wireless data reception.Data received through the wireless module, the microcontroller serial interface received data and passed to the master chip AT89S8252 processing, when there is wireless data transmission, the priority to receive data The display main program flow chart is shown in Fig. Figure 6 shows the flow chart of the wireless data receiving subroutine. Whether the display can clearly show the contents of the main aspects from the following aspects: 1) single-chip control LED bright off time: T = S / V, S for the LED surface width, the motor rotation line speed; 2) Balance; 3) ambient light contrast.
4 concluding remarks
The system shows the English characters using 16 × 32 dot matrix, Chinese characters with 32 × 32 dot matrix, the graphics using 64 × 64 dot matrix way. People can see a clear dynamic display within 360 degrees. Using Visual Basic 6.0 prepared by the mold software, can take the mold and send data through the COM port. Can be real-time input content, to achieve the character graphics touch; can handwriting input graphics, can achieve arbitrary graphics display, can display a simple dynamic picture. The system uses Bluetooth-like technology, data transmission is stable, accurate and reliable. Wireless and wired two data transmission methods can ensure the accurate transmission of data. Select the LED surface width of 3mm, the axis to the dot matrix LED distance of 160mm, full screen can display about 22 Chinese characters, display the size of the content determined by the above conditions and speed. The system has the characteristics of simple structure, unique viewing angle, novel design, easy to use and so on. It has high social application value and can be widely used in commercial advertising, conference notification, slogan, environment decoration and visual persistence in higher physics teaching demonstration experiment etc.