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1、题 目： LED 点阵显示器1 引言：自20世纪80年代后期开始，随着LED制造技术的不断完善，在国外得到了广泛的应用。在我国改革开放之后，提别是进入90年代国民经济的高速增长，对公众场合发布信息的需求日益强烈。而LED显示屏作为信息传播的一种重要手段，已经成为城市信息现代化建设的标志,LED显示屏随着社会经济的不断进步，以及LED制造技术的完善，人们对LED显示屏的认识将会越来越深入，其应用领域将会越来越广；LED显示屏经多年的开发、研制、生产，其技术目前已经成熟。 现在各种广告牌不再是白底黑字了，也不再是单一的非电产品，而是用上了丰富多彩的LED电子产品，为城市的增添了一道靓丽的风景。而且
2、它采用低电压扫描驱动，具有耗电少、使用寿命长、成本低、发光效率高、故障少、视角大、可视距离远、可靠耐用、组态灵活、安全、响应时间短、绿色环保、控制灵活、色彩丰富以及对室内外环境适应能力强等特点。近年来LED显示屏市场得到了迅猛的发展，已经广泛应用到银行、邮电、税务、机场、车站、证券市场及其它交易市场、医院、电力、海关、体育场等需要进行多种公告、宣传的场合。 因此，学习LED系统原理与工程技术很有必要。 2.1 LED显示屏的开发环境2.1.1 显示屏驱动电路的选择 方案一 在禁止使用专用的LED控制芯片的情况下采用通用芯片74LS595，其具有8位锁存、串并移位寄存器和三态输出，可以用它的锁存
3、功能实现硬件电路对数据的刷新。其特点是控制信号简单，级联方便，芯片数量少。 方案二 我们可以用移位寄存器74HC164和译码器74HC138配合三级管来实现LED点阵显示的行列控制.但由于三极管需要量太大使电源超负荷，将导致屏幕暗亮。综合考虑，我们采用方案一。2.1.2 亮度连续可调 方案一 通过在软件中调节刷新频率。刷新频率高的时候,连续点亮的时间短,显示屏亮度低,当刷新频率调低时,连续点亮的时间延长,显示屏变亮。因此通过调节占空比来实现显示屏亮度的调整。但是由于软件调节亮度变化不连续.不能实现连续的亮度调节。并且会出现闪烁。调节的效果不明显。方案二 通过调节电位器来改变电压,实现亮度的调节
4、。调节电位器实现线形电压调整,从而控制三极管使显示屏压降发生改变。从而达到连续调节亮度的目的。电位器的调节范围较大，因此用此方法来调节。 考综合虑，我们采用方案二。图2.1 简单单片机处理框图2.1.3 串行口的选择方案一 采用RS485来进行长距离（1200M）的传输，RS-485总线通信模式由于具有结构简单、价格低廉、通信距离和数据传输速率适当等特点而被广泛应用.2但RS485总线存在自适应、自保护功能脆弱等缺点，如不注意一些细节的处理，常出现通信失败甚至系统瘫痪等故障而且总线本身存在许多的局限性，效率低，实时性差，通信的可靠性低，应用不灵活。方案二 采用MAX232来进行串行的传输, 用
5、串行通讯的好处是简单，抗干扰性强.由于本系统有寄存器,因此不需要远距离传输,因此MAX232已经足够满足要求。并且可直接和PC机接口，2不用外加协议转换电路。综上所述，方案二比较合理。3 系统的具体设计与实现3.1 系统总框图图3.1系统原理图3.2 硬件条件 用常用的AT89S52控制。技术比较熟练，应用广泛，9现在的51系列技术硬件发展的也非常得快，也出现了许多功能非常强大的单片机，因此使用单片机可以实现要求的基本功能。 都是8051的内核，只不过52的内部资源比51稍多，8比如增加了一个16位的计数器T2，当然相应的特殊寄存器(SFR)也有了一点变化，另外52的内存也从51的128字节提
6、高到了256字节，ROM也从2K提高到4K，可以装下更大的程序，但是若单从运算速度来讲，由于二者都是8051的直系后代，基本上可以认为二者运算性能相同。 考虑到内存的增加对较复杂的程序带来的好处，52的总体性能是要比51好不少的。1 另外S52比C51还增加了ISP功能，1就是在线可编程功能，这可是很有用的功能哦，首先是省去购买编程器的钱，另外，对于买不起仿真器或希望能板上调试（就是插在成品电路板上调试）的人来说十分有价值，你可以随时更新插在电路板上的单片机的程序，十分方便。当然S51也具备这一功能，C51和C52都不具备，不过他们也已经停产了，7现在电子市场能买到的大都是S系列的。图3.2
7、8*8点阵外观及引脚图 采用4个8*8LED显示模块，构成16行*16列点阵显示点阵显示屏。4片8*8点阵LED显示模块利用总线形组成一个16*16的LED点阵，用于同时显示1个1616点阵汉字或4个168点阵的字母字符或数字。4单元显示屏可以接收来自控制器（主控制电路板）或上一级显示单元模块传输下来的数据信息和命令信息，并可将这些数据信息和命令信息不经任何变化地再传送到下一级显示模块单元中，因此显示板可扩展至更多的显示单元，用于显示更多的显示内容。3.3 软件部分3.3.1 LED显示屏驱动电路4采用74HC154译码器。将从AT89S52里出来的列信号通过74HC154级联而成的16位的信
8、号输出端连接到16*16的点阵LED的输入端，作为点阵的行驱动信号。从89S52输出四个信号分别输入到级联的74HC154译码器，2然后输出16位行信号，经过16个200欧姆的电阻，再输入到16个PNP（8550）三极管的B极来进行对行信号的放大，其中所有的三极管的E极相连接+5V的电源，所有的C极接16个LED点阵的行型号引脚，得到的信号作为点阵LED 的行输入信号。通过对154的四个输入信号进行控制，改变行信号来控制二极管的亮、灭来显示出所要求的字符、汉字。行驱动电路：每个LED管亮需要7mA的电流，那么64个同时亮就需要448mA的电流，所以我们要对列进行驱动，我们采用晶体管8550对列
9、信号进行放大，使LED点阵能够正常显示。其驱动电路如下：图3.3 74HC154行驱动线路图3.3.2 LED显示器列驱动电路4 此电路是由集成电路两个级联74HC595构成的，它具有一个8位串入并出的移位寄存器，可以实现在显示本行各列数据的同时，传送下一行的列数据。图3.4 74HC595列驱动线路图3.4 亮度连续可调用一个200欧姆的电阻和8550的三极管组成，可以对LED的压降进行调节，以到达连续改变亮度。5此是作为对亮度的调节的方法。3.5 刷新频率的计算根据人眼的视觉的暂留特性，50HZ是适宜的刷新频率，所以CPU的刷新频率一般不低于60HZ，但是刷新频率太高的话，会使显示屏的亮度
10、降低，所以刷新频率有最高值要求，本设计最高刷新频率为600HZ。1 3.6 键盘待添加的隐藏文字内容2键盘是使用比较简单的独立式键盘，而且具有指示功能模块电路图如图图3.5 按键开关线路图 键盘各项功能如下：显示模式键：键可以模式选择五种模式，预存汉字、预存符号、SD卡信息、时钟和PC数据显示。滚动模式键：可以控制二种滚动模式，在正常显示模式下实现左、右滚动。循环模式键：可以控制定时循环模式。时间调整键：即时间设定键，在时钟显示模式下，可配合加减键循环设置时、分、秒。定时键：按下时，显示当前的循环间隔的时间，可利用加减键进行间隔控制调整。刷新频率键：按下后，显示刷新频率，可利用加减键调整。滚动
11、速度键：按下后可以显示当前的速度，利用加减键调节滚动速度。加、减键：配合其他键，在各种模式下，实现调整。复位键：复位系统。外文翻译： LED Light Emitting Diode Light Emitting Diode is the abbreviation of, is a kind of can convert electric power into the visible semiconductor. Of LED dot matrix is arranged by leds of display devices, in our daily life in the electric
12、 everywhere, very common is also well known. In particular, it belongs to the luminous type cold light, efficiency and heat is ordinary light devices incomparable, it USES low voltage scanning drive, has: less consumption, long service life, low cost, high brightness, low malfunction, perspective, v
13、isible distance, specification product, reliable and durable, application flexible, safety, response time is short, the green environmental protection, the control of flexible, etc. At present, the LED display screen as a new generation of information transmission media, has become a symbol of the c
14、ity information modernization construction. With the economic and social progress, and LED display technology continues to improve, people on the LED display know will more and more thorough, its application field, will be more and more widely. This design is simple to use single chip AT98S52 as the
15、 main control module, use the periphery of the simple circuit to drive 16 * 16 matrix LED display. Since the 1980 s began, with the continuous improvement of the LED manufacturing technology, in foreign a wide range of applications. After the reform and opening in China, especially in the 90 s put n
16、ational economic growth, for public release information needs become increasingly strong.And the LED display as information transmission of a kind of important means, has become a symbol of the city information modernization construction, the LED display with the economic and social progress, and LE
17、D to the improvement of the manufacturing technology, people on the LED display know will more and more thorough, its application field, will be more and more wide; The LED display after years of development, the development, the production, the technology currently has the maturity.Now all kinds of
18、 billboard is no longer a white background with black text, also no longer is a single the electric products, but to use the rich and colorful LED electronic product, for the city added to the beautiful beautiful scenery. And it with low voltage scanning drive, has less consumption, long service lif
19、e, low cost, high luminous efficiency, low malfunction, perspective, visible distance, reliable and durable, configure, flexible, safety, response time is short, the green environmental protection, control and flexible, rich color of indoor and outdoor environment adaptable etc. Characteristics. In
20、recent years the LED display market has developed rapidly, and has been widely applied to the bank, post and telecommunications, taxation, airport, station, securities market and other trading market, the hospital, the electric power, the customs, the stadium to perform a variety of public announcem
21、ent, propaganda occasion.Therefore, the study LED system principle and engineering technology is necessary. Plan a through the software refresh frequency regulation. The high frequency refresh, continuous light of short time, the screen brightness low, when lower frequency refresh, extend the time o
22、f continuous light, screen to brighten. So by regulating the board of empty realize the adjustment of the screen brightness. But because the software adjust brightness changes discontinuous. Cant achieve continuous brightness to adjust. And there will be flashing. The effect of regulation is not obv
23、ious. Scheme ii by adjusting the potentiometer to change voltage, realize the brightness the adjustment. Adjust potentiometer realize linear voltage adjustment, so as to control transistor to scroll pressure drop to change. So as to achieve the purpose of continuous adjust brightness. The adjustment
24、 of the potentiometer range is very large, so how to use this method to adjust. Take an examination of comprehensive safety, we use the scheme ii. Use the conventional AT89S52 devices control. More skilled technology and wide application, 9 now 51 series technology hardware development is also very
25、fast, also appeared many function very powerful microcontroller, so using SCM can realize the basic function of requirements.Are the core of 8051, just 52 of the internal resource of a little more than 51, 8 such as increased a 16 bit counter T2, of course, the corresponding special register (SFR) a
26、lso has been a change, in addition to the memory of the 52 from 51 128 bytes of increased to 256 bytes, ROM from 2 K increased to 4 K, can hold more program, but only from the operation speed if terms, because both the direct descendant of 8051, basically can believe that the same operation performa
27、nce The 74 HC154 decoder. AT89S52 came out from listed by 74 HC154 signal a cascade of 16 signal output connected to 16 * 16 matrix of LED input, as do the driving signal matrix. From 89 S52 output signal input to four respectively cascade of 74 HC154 decoder, 2 and then output 16 line signal, after
28、 16 200 ohm resistance, then enter to 16 a PNP transistor (8550) of the B to signal to a line of amplifier, including all of the transistors E very connected + 5 V power, all the C very take 16 of LED dot matrix line model pin, get the signal as the line of input signal lattice LED. Through to the 154 four input signal control, change the line of control signal to light, to destroy the diode shows the required character, Chinese characters.
