Design and Implementation Of Interfacing Of 5x7 Matrix Led Display To 8051

Transcription

1 Design and Implementation Of Interfacing Of 5x7 Matrix Led Display To 8051 BY Ami Goswami (IU ) Vatsal Shah (IU ) Department of Electronics & Communication Engineering Indus Institute of Technology

2 INDEX Abstract... 3 List of Figures... 4 List of Table... 4 Ch. 1 Introduction Introduction Objective Scope and Limitation... 5 Ch. 2 Review of Related Studies of LED matrix Theory of LED dot matrix display Description of LED Dot Matrix vs. 7-segment Display Advantages of LED Dot Matrix Construction Why used dot matrix? Definition of LED Driver... 7 Ch. 3 Design Specifications What do we need? Basic component required How does it work? Hardware Design ULN2003A Driver IC Software Description Assembly code: Ch.4 Procedure and Results Procedure Simulation and results Conclusion References... 15

3 Abstract A 5x7 matrix LED Display board with 8051 microcontroller has been designed. The LED s are connected like a matrix with 7 rows of 5 LED s per each row is designed on a board to display. For a 5x7 LED matrix, it is impractical to assign one I/O pin per LED, as a 5x7 matrix requires 35 I/O pins. These characters are switched continuously with a delay of 05msec. This design can be extended to number of units by using shift registers to display a message consisting of many numbers of characters. By controlling the data bits connected to the LED s, we can display any character. The 5x7 LED matrix display with 35 LED s are arranged in 7 rows and 5 columns structure. The purpose of ULN2003A here is to drive the column lines of the display. ULN2003A is a high voltage (50V), high current (500mA per channel) Darlington transistor array. Each IC has 7 channels with individual output clamp diodes. ULN2003A an active high device, which means logic high must be applied to the input to make the corresponding output high. The software required for displaying character A, B, C, etc. on the LED matrix, with a delay between each character display has been developed in assembly of The hex code is downloaded on to the AT89s51 microcontroller and is verified by interfacing the microcontroller pins for any given character, a corresponding pattern of LED is generated and is used to display the character at run time. The application and advantages that can be used at public transport places like bus stop, railway station, and airport. Displaying various important messages in hospitals, schools, colleges. In future development we can use GSM technology to receive the data from remote location. 3

4 List of Figures Figure No. Figure Title Page No X7 LED matrix Interfacing 5x7 matrix LED display to ULN2003A drive IC pin configuration and internal logic diagram LED display Simulated circuit of 5X7 Display List of Table Table No. Table Title Page No. 3.1 Code table 20 4

5 Ch. 1 Introduction 1.1 Introduction Visual impact is most effective mode of influencing human s minds main aim of advertisements etc. a display device serves this purpose. A display device is a device for presentation of information for visual reception, acquired, stored, or transmitted in various form. The display device is use to display the information on machines, clock, railway departure indicator and many other devices require a simple display of limited resolution. The display consist of a matrix of lights or mechanical indicator arranged in rectangular configuration (other shapes are also possible) such that by switching on or off the text or graphics can be displayed. Our initial goal was to create a display that would be useful and interactive in order to attract attention. In the development of our main goal, the modular LED array, we found that we would be dealing with three major components, Integrated circuits consisting of microcontroller, resistor array, and LED driver. Printed circuit board technologies, as well as software involved in their design. Programming in assembly language to drive the microcontroller and scan through individual row of LED s with the data needed to produce a message. For moving a message on display we design a A dot-matrix display contains 5x7 dots (LED s), the LED s are connected like a matrix with 7 rows of 5 LED s per each row and a matrix is designed on a board to display characters. LED dot matrices are very popular means of displaying information as it allows both static and animated text and images. Perhaps, you have encountered them at gas stations displaying the gas prices, or in the public places and alongside highways, displaying advertisements on large dot matrix panels. 1.2 Objective The objective of this study is to provide a way of displaying information electronically. That could result to effectual information dissemination. 1.3 Scope and Limitation This study is only intended to display information via alphanumeric and commonly used characters like dot (.), comma (,), etc. which means that it is not capable of showing animated figures or drawings since the inputs allowed are alphabets, numbers and special characters only. 5

6 Ch. 2 Review of Related Studies of LED matrix 2.1 Theory of LED dot matrix display In a dot matrix display, multiple LEDs are wired together in rows and columns. This is done to minimize the number of pins required to drive them. For example, a 5 7 matrix of LEDs (shown below) would need 35 I/O pins. By wiring all the anodes together in rows (R1 through R7), and cathodes in columns (C1 through C5), the required number of I/O pins is reduced to 16. Each LED is addressed by its row and column number. In the figure below, if R4 is pulled high and C3 is pulled low, the LED in fourth row and third column will be tuned on. Characters can be displayed by fast scanning of either rows or columns. FIG.2.1 5X7 LED matrix 2.2 Description of LED Light-emitting diodes (LEDs) are semiconductor devices that illuminate solely by motion of electrons. When forward-biased, these things emit light. LEDs provide a cheap and convenient way to display information electronically, fit easily into an electrical circuit, and are durable. 2.3 Dot Matrix vs. 7-segment Display LEDs are often arranged in patterns to display information. The 7-segment configuration of an LED arranged in the form of digit 8 can be restrictive in that it does not adequately allow the display of some alphanumeric characters. By contrast, the versatility of a dot matrix arrangement allows an LED unit to display complicated shapes. A 5x7 LED dot matrix is the appropriate device for displaying characters. 6

7 2.4 Advantages of LED LED advantages are energy efficient, environmental, produce the intended light and runs cool. It lights up quickly, fully dimmable, operates silently, and has good color rendering. One of LED savings is on the carbon dioxide (CO2) emission of power plant in producing electricity, which helps protect Earth. LEDs are even better that traditional lighting. Factors like energy savings, energy efficiency and environmental advocacy. 2.5 Dot Matrix Construction The two dot matrix configurations are the LED matrix with a common anode for LEDs in a row - all of the anodes in each row is common, and LED with a common cathode for LEDs in a row all the cathodes in each row is common. 2.6 Why used dot matrix? The dot matrix is the most versatile display in our line of LED displays. It is suitable for any application that requires numeric, alphabetical and symbolic/graphic information to be displayed. Choose a smaller pixel size for a crisper message and combine multiple modules for larger displays. Practically, a LED dot matrix is better than creating a panel composed of single LEDs because a matrix provides proper alignment and saves a huge amount of soldering. 2.7 Definition of LED Driver IC drivers are devices that provide the required current and voltage needed to turn power switching elements on or off such as LED displays filament lamps including5x7 Dot Matrix Display based on the logic output signals of a digital signal processor (DSP) and microcontroller or other logic device. The ULN2003 LED driver is a high voltage, high-current Darlington arrays containing Darlington pairs with common emitter configuration. Each channel rated at500 ma and can withstand peak currents of 600mA which can drive wide range of loads including solenoids, relays, DC motors; LED displays filament lamps, thermal print heads and high power buffers. Suppression diodes are included for inductive load driving. 7

8 Ch. 3 Design Specifications 3.1 What do we need? Micro controller based interface using ICAT89S51 Display size: 8x34 pixels, (26.5.cm) x (5.5.cm) Input Power: 8-12V DC, 500mA LED driver interface Crystal Power-On LED indicator Data receiving LED Resistors 3.2 Basic component required ICAT89S51 Control Circuit Display Board Computer 3.3 How does it work? We need to dump the code which we have written in C compiler into the ICAT89S51, and later we assemble the control circuit and fix connectors and also the serial port to pc. Now we setup the software into computer and when we type the messages in the computer we get the display. This is how it works. 3.4 Hardware Design : The Block diagram of 5x7 LED matrix is show in the figure. The 5x7LED matrix display with35 LED s are arranged in 7 rows and 5 columns Structure named as display character as shown in the figure 1. The data is provided to rows and columns through program loaded in IC1 AT89S51. Now the rows are connected to 89S51 through port p0. 8

9 FIG3.1.1Interfacing 5x7 matrix LED display to ULN2003A Driver IC The purpose of ULN2003A here is to drive the column lines of the display. ULN2003A is a high voltage (50V), high current (500mA per channel) Darlington transistor array. Each IC has 7 channels with individual output clamp diodes. ULN2003A an active high device, which means a logic high must be applied to the input to make the corresponding output high. The input pins are designated as 1B, 2B, 3B, 4B, 5B, 6B, 7B while corresponding output pins are designated as 1C, 2C, 3C, 4C, 5C, 6C, and 7C. The pin configuration and simplified internal logic of ULN2003A is shown in the figure below. FIG ULN2003A drive IC pin configuration and internal logic diagram. 9

10 3.6 Software Description The software required for displaying characters A on the LED matrix. The hex code is downloaded on to the 89S51 microcontroller and is verified by interfacing the microcontroller pins to the pins of the board. For any given character, a corresponding pattern of LED is generated and is used to display the character at run time. The equivalent data bytes required for the Display of A character were computed and stored at internal ram address and were transmitted sequentially by monitoring the TI flag of the SCON register. 10

11 3.7 Assembly code: #include <reg51.h> VoidMSDelay (unsigned int); sbit R1=P0^0; sbit R2=P0^1; sbit R3=P0^2; sbit R4=P0^3; sbit R5=P0^4; sbit R6=P0^5; sbit R7=P0^6; sbit C1=P1^0; sbit C2=P1^1; sbit C3=P1^2; sbit C4=P1^3; sbit C5=P1^4; //Rows connected with Port P0 //Columns connected with Port P1 void main(void) { while(1) { P1 = 0x01; //To print word EC P0 = 0x80; MSDelay(5); P1 = 0x02; P0 = 0xB6; MSDelay(5); P1 = 0x00; P0 = 0x00; MSDelay(5); P1 = 0x08; P0 = 0x80; MSDelay(5); P1 = 0x10; P0 = 0xBe; MSDelay(5); } } voidmsdelay(unsigned int time) { unsignedinti,j; for (i=0;i<50;i++) for (j=0;j<time;j++); } 11

12 Ch.4 Procedure and Results 4.1 Procedure Suppose, we want to display the word EC. We will first select the column C1 (which means C1 is pulled low in this case), and deselect other columns by blocking their ground paths (one way of doing that is by pulling C2 through C5 pins to logic high). Now, the first column is active, and you need to turn on the LEDs in the rows R1 through R7 of this column, which can be done by applying forward bias voltages to these rows. Next, select the column C2 (and deselect all other columns), and apply forward bias to R1,R5 and R7 and so on. Therefore, by scanning across the column quickly (> 100 times per second), and turning on the respective LEDs in each row of that column, the persistence of vision comes in to play, and we perceive the display image as still. Fast scanning across the columns results in a steady display. Fig3.1 Display Device 12

13 ROW\COL C1 C2 C3 C4 C5 R R R R R R R Table No. 3.1 code You should have noted that across each row, one pin is sourcing the current for only one LED at a time, but a column pin may have to sink the currents from more than one LED. For example, the column C1 should be able to sink the currents from 6 LEDs while displaying the WORD EC. A microcontroller s I/O pin cannot sink this much of current, so external transistor arrays are required. 13

14 4.2 Simulation and results Simulated circuit to print any word on 5X7 matrix using 8051uC as shown below: Fig 3.7 Simulated Circuit of 5X7 Display 4.3 Conclusion The display consists of a dot matrix of lights arranged in a rectangular configuration such that by switching on or off selected text or graphics can be display. A dot matrix controller converts instructions from a processor into signals which turns on or off lights in the matrix so that the required display produced. 14

15 5 References Muhammad Ali Mazidi (2012), The 8051 Microcontroller and Embedded System, Second Edition, Pearson datasheet for-led-current-drive mpg/samplefinalprojectreport.pdf 15