led matrix display project report

KATHMANDU UNIVERSITY SCHOOL OF ENGINEERING

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

PROJECT REPORT

LED Matrix Display

Submitted To:

Mr. Jeevan Shrestha

Project Supervisor

Department of Electrical and Electronics Engineering

School of Engineering

Kathmandu University

Submitted By:

Kabool Neupane (EE1, 22017)

Bigyan Chapagain (EE2, 22031)

Praveen Shrestha (EE2, 22042)

Manish Prajapati (EE2, 22048)

June 27, 2010

i

ABSTRACT

The project LED Matrix Display is concerned with the construction of a two dimensional

arrangement of LEDs in a rectangular arrangement for the purpose of displaying English

Alphabets (Upper Case) and decimal numerals. The characters to be displayed are entered

using a computer. Therefore, in this project the computer functions as an input device and

LED Matrix Display functions as an Output device. A computer program shall also be

included in the project to create a user-interface environment to enter the characters and

numbers to be displayed.

ii

ACKNOWLEDGEMENT

We express our sincere thanks to our project supervisor Mr. Jeevan Shrestha for his kind

support, encouragement and guidance throughout the course of our project work. It is

because of his continuous support we were able to acheive much in this project work. We

would also like to express our sincere gratitude to our project coordinator Mr. Samip Malla

for his guidance on this project course. Similarly we would like to thank all the teachers

and lab incharges who have helped us in every possible way. This project has helped us a

lot in our understanding and experience. Besides, it has been a great excitement doing this

project and we hope to achieve much more in future. We, therefore look forward to your

kind support in the years to come.

iii

SYMBOLS AND ABBREVIATIONS

A. Symbols

Symbol Description

Ohm

K Kilo ohm

s Micro second

mA Milli ampere

B. Abbreviations

Abbreviation Full Form

LED Light Emitting Diodes

PC Personal Computer

IC Integrated Circuit

PCB Printed Circuit Board

iv

LIST OF FIGURES

Fig. No. Title Page No.

1. Block Diagram 2

2. Parts of a LED 4

3. The inner workings of LED 4

4. Eye response to color 5

5. LED Matrix 6

6. Transistor as a switch 7

7. Pulse driven LED 8

8. Pin configuration of 4017 9

9. Timing diagram of 4017 10

10. Cascade 4017 11

11. Parallel port 11

12. Parallel port configuration 12

13. IC 74244 13

14. Block diagram 14

15. Cascaded counter implementation 15

16. Cascaded LED Matrix 16

17. Code Protection circuit 17

18. Flowchart of the program 19

19. Flowchart to detect the column of matrix 20

20. LED Matrix component setup 21

21. Master transistor switch setup 21

22. Output waveform from data pin 6 22

23. Output waveform from data pin 1 23

24. LED Matrix display 24

25. LED Matrix display in PCB 27

26. Gantt chart 29

v

LIST OF TABLES

Table No. Title Page No.

1. Pin configuration of 4017 9

2. Ring counter sequence 10

3. Port pins in our project 12

4. Address of registers 13

5. Cost Estimation 26

vi

TABLE OF CONTENTS

Abstract i

Acknowledgement ii

Symbols and Abbreviations iii

List of Figures iv

List of Tables v

Chapter 1: Introduction 1

1.1 Background theory and Objectives 1

1.2 System overview 2

1.3 Methodology 2

1.4 Overview of the Report 3

Chapter 2: Technology and Literature Survey 4

2.1 Components used 4

2.1.1 LEDs 4

2.1.2 LED Matrix configuration 6

2.1.3 Transistor as a switch 7

2.1.4 LED Driving Circuit 7

2.1.5 Counter IC 4017 9

2.1.6 Parallel port 11

2.2 Software used 13

Chapter 3: System Analysis and experiments 14

3.1 System Analysis 14

3.1.1 System analysis 14

3.1.2 Overall description of the circuit 15

3.1.3 Computer Program 18

3.2 Mathematical calculation and experiments 21

3.2.1 Mathematical calculation 21

3.2.2 Experimental observation 22

Chapter 4: Product description and performance 24

4.1 Product description 24

4.1.1 Physical description 24

4.1.2 Cost Estimation 26

4.2 Product performance 27

4.3 Final product 27

vii

Chapter 5: Discussion and performance 28

5.1 Gantt chart 29

Biblography 30

Appendix A: Mathematical Calculations 31

Appendix B: Computer program 33

Appendix C: PCB Circuit 50

Appendix D: Datasheets of components 52

D1: Datasheet of BC548

D2: Datasheet of 1N4148

D3: Datasheet of SL100

D4: Datasheet of 74244




1

CHAPTER 1

INTRODUCTION

1.1 Background Theory and Objectives

1.1.1 Background Nowadays, we can see various ways of visual information everywhere. One of the

most common sights that we can see today is the LED Matrix Display. Nowadays

these are extensively used in streets, malls, buildings, parks and other public places.

LED Matrix Displays have become a basic way of visual information since they are

cheaper and more reliable than LCD displays and other expensive display devices.

Now, considering the growing popularity of the LED Matrix display, we decided to

construct a small home based PC controlled LED Matrix display so that it could be

used for small household purposes as well as for various entertainment purposes.

Therefore our project deals with the construction of a LED Matrix display whose

input device is a computer.

1.1.2 Objectives This project mainly focuses on the following topics

To study existing concepts and required materials related to a LED

Matrix Display

To design a proper circuit, for a LED Matrix Display, which is most

suitable for our case.

To create a computer program to enter data to be displayed by the LED

Matrix Display.

To make the program an user interface program.

2

1.2 System Overview

Figure 1: Block Diagram

The Operational framework of the LED Matrix display is shown in Figure 1. The

figure illustrates that the computer port controls the rows of the matrix and the

columns are controlled by the counter. Furthermore, Computer triggers the counter of

the circuit. This helps in synchronizing the timing pulse of counter with the computer

signal.

1.3 Methodology In order to complete this project work we have taken help from various books,

magazines, websites, and by consulting to teachers and seniors. The procedure taken for

the successful design and operation of LED Matrix Display comprises of mainly two

parts i.e.

Hardware part

Software part

1.3.1 Hardware Part For hardware part, the following procedures were taken:

- Firstly literature survey was conducted. - Different approaches to the circuit design were considered and the best

was chosen.

- The circuit was implemented on a bread board. - Various experiments were undertaken. - The overall system was analyzed. - Constantly, the circuit in bread board was upgraded to get the best

performance.

- Finally, the circuit was completed in PCB, obtaining successful output.

Power Flow

Signal Flow

Computer Control

LED Matrix Display

Control Column

Con

trol

Row

Counter

3

1.3.2 Software Part For software part, we applied the following procedures.

- The user interface program was decided to be implemented in C programming language.

- The algorithm for the program was discussed. - Then the program was written and implemented in virtual LED Matrix

environment.

- For simplicity and user friendliness, the program was further modified with function modules.

- The program was implemented in the hardware part. - Various problems were encountered, and solved. - Finally the successful output was obtained.

1.4 Overview of the report This report gives an overview of the project LED Matrix Display. In the next pages, we will discuss about the processes involved in the project. We will also be dealing

with the technologies used. This report also discusses about the C program

implementation on accessing and controlling the parallel port. To sum up, this report

gives any reader a complete overview of our project on LED Matrix Display.

4

CHAPTER 2

TECHNOLOGY AND LITERATURE SURVEY

This project can broadly be divided into two sections:

Software part: Software part includes programming design for the system. In this part, a C program is developed in order to send information to LED

Matrix from PC via the parallel port.

Hardware part: Hardware part includes the design and construction of the hardware parts of the system. Design of LED Matrix and construction of

supporting elements like development of ring counter, implementation of

transistors as switch and LED driving circuits are included in this portion.

Firstly, we will discuss about main components used in the circuit and their structure.

Later on, their working mechanisms and their effect in the circuit will be discussed.

2.1 Components used

2.1.1 LEDs As the name implies, a Light Emitting Diode (LED) is a diode that gives visible or

invisible (infrared) light when energized. LEDs are diodes usually constructed by

GaAs. In such semi-conductor p-n junction, during the recombination of holes and

electrons, the energy is dissipated in the form of photons resulting in the emission of

light.

Figure2: Parts of a LED

aaaaALELlLLED

Figure3: The inner workings of LED

5

The color of the LED used for the LED Matrix Display is red. The reason we have

selected this LED is because it is known that human eyes are least sensitive to red

color. In other words, shades of red light are least sensitive to our eyes. This implies

that slight variation in the brightness of the red LED lights will mostly go unnoticed

by our eyes. This fact is crucial in our product since we require constant brightness of

all LEDs. Even though considerable thought and careful designing has been done to

maintain constant brightness, it is nevertheless probable that slight error will arise,

due to imperfect and non-uniform electronic components, which is inevitable.

Therefore, red lights provide the perfect solution for this problem.

Figure 4: Eye Response to color

Figure 4 illustrates that RED and Blue lights are least sensitive to human eyes. While

this fact is advantageous to our product as discussed earlier, it however implies that a

red LED must have a much stronger efficiency than a green one to be visible at the

same intensity. It means that sensitivity to wavelength and sensitivity to intensity are

different. For a green LED and red LED to be of equal intensity, the latters efficiency

should be greater or in other words power transfer should be greater. Considering this

fact it is ensured that optimum intensity of the red LEDs used in the product has been

maintained under safe limits.

Generally Red LEDs are constructed using GaAsP and their threshold voltage is

usually 1.3 V.

RED

GREEN

BLUE

6

2.1.2 LED Matrix Configuration:

The dimension of LED Matrix chosen for our project is 55. It is chosen since it is

relatively easy to design a character or a number in such configuration. Furthermore,

since the project implies the use of parallel ports with 8 output pins, the matrix can be

friendly for the port interface. In any case, a LED matrix with 55 dimension implies

controlling of 25 LEDs at any time. To reduce this difficulty the configuration of the

LED matrix is done in following way:

The configuration shown in figure 5 allows reduction of points to be controlled for the

LED Matrix Display. Instead of controlling each individual LED, the configuration

allows us to control entire row and column at any instance. In the configuration, the

anodes of the LEDs are connected along a row and the cathodes are connected along a

column. This allows control of an individual LED in any instance. For example, if we

wish to control a LED at position 22, we can do it by controlling voltage supply at

2nd

row and ground supply at 2nd

column. In this way any LED in the matrix can be

controlled. In case of 55 LED matrix, this configuration reduces the control points to

10 from 25.

For further reduction of number of control pins, we have used a counter to

automatically control entire column. By doing so, the control pins are further reduced

to half.

Figure 5: LED Matrix

Configuration

7

2.1.3 Transistor as a Switch

Transistor is a three layer semi-conductor device consisting of either two n- and one

p-type layers of material or two p- and one n-type layers of material. Both types can

be used for switching purpose. In such application a transistor works in saturation and

cut off mode. The transistor we have used in the project is an npn type transistor

BC548. This transistor has been used for switching purpose. It is set in common

emitter configuration. The reason behind the use of transistor as switch is to control

the power supply to the LEDs.

VCC

VCC

1

0

23

2

2.1.4 LED Driving Circuits:

LEDs are current driven elements. It requires a constant current in order to maintain

constant brightness. A LED Driving Circuit is a circuit that is designed to maintain

constant brightness in LEDs.

LED Driving Circuit:

- Delivers a constant average current under all conditions.

- Controls ripple current at acceptable level under all conditions.

- A LED Driving circuit is a type of power conversion circuit

that delivers constant current instead of constant voltage.

If a constant current is not maintained, a pulse circuit can be designed to generate

maximum brightness from a LED without damaging it.

Figure 6: Transistor as a switch

Common configuration for tran

istor as a switch

8

Pulse Circuit:

- A sufficient current pulse for the maximum brightness of a

LED is sent at a suitable frequency.

- The pulse duration saves a LED from over heating by sending

the average of current pulses while maintaining the brightness

of a LED.

- The pulse duration and synchronization is maintained by

providing the same timing pulse of computer signal to the

counter.

VCC

5V

1

2

3

4

5

7

11

Figure 7: Pulse Driven LED

Row

s co

ntr

oll

ed v

ia p

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port

Column connected to counter output

Code protection output

9

Brief Description:

The previous diagram represents the configuration of the LED driving circuit at any

instance of time. Since any column is controlled by a counter, no two columns can be

active at a same time. Therefore at any instant only one such column is active. Now

the transistors controlled by the parallel port provide a constant current to each LED

connected to it. This configuration is thus better than the previous ones, which we

have implemented, which failed to ensure constant current to each LED at all

conditions. The new configuration along with the pulse driving circuit thus ensures

better results.

2.1.5 Counter (IC 4017)

Figure 8: Pin configuration of IC 4017

PIN NO. SYMBOL NAME AND FUNCTION

3, 2, 4, 7, 10, 1, 5, 6, 9,

11 Q0 to Q9 decoded outputs

8 GND ground (0 V)

12 Q5-9 carry output (active LOW)

13 CP1

clock input (HIGH-to-LOW, edge-

triggered)

14 CP0

clock input (LOW-to-HIGH, edge-

triggered)

15 MR master reset input (active HIGH)

16 VCC positive supply voltage

Table 1: Pin configuration of IC 4017

The 4017 counter has ten outputs which go high in sequence when a source of pulses

is connected to the clock input and suitable logic is applied to Reset and Enable

inputs.

Internally 4017 contains five bistable subunits. These are interconnected in a pattern

known as Johnson counter. The Johnson Counter is a counter in which the Q output of last F/F is connected to the serial input of the first stage. The outputs of bistables

are then decoded to give ten individual outputs.

10

The timing diagram for the 4017 counter is shown below:

Figure 9: Timing Diagram of 4017

The behavior of a 3 stage Johnson Counter can be understood as following:

(ALL F/F is reset in the beginning)

Table 2: Ring Counter sequence

5 stage Johnson counter has 10 decoded outputs (2n output states). The decoder uses 2

input NOR gates to give 10 decoded outputs.

Clock Pulses D Input Output A Output B Output C

0 1 0 0 0

1 1 1 0 0

2 1 1 1 0

3 0 1 1 1

4 0 0 1 1

5 0 0 0 1

6 1 0 0 0

11

Cascading 4017:

Figure 10: Cascaded 4017

It is essential not to enable the counter on CP1 when CP0 is HIGH, or on CP0 when

CP1 is LOW as this would cause an extra count.

We cascade the 4017 IC for extending the number of decoded outputs. Decoded

outputs are sequential within each stage and from stage to stage with no dead time

(except propagation delays).

2.1.6 Parallel Port

Introduction

Parallel port is a type of interface located at the back of PC used for communication

and device control. Usually, it is used for connecting printer, so also called printer

port or centronics port. The type of parallel port present in the computer is D-Type 25

Pin female connector. There may be also be D-Type 25 pin male connector. Since it is

easy to program and faster compared to other ports, nowadays it is very much popular

for controlling external devices. But the main disadvantage of parallel port is it

requires more number of transmission lines, so it cannot be used for long distance

communication and is so used for short distances only.

In our project, it is used as the bridge between the hardware component and the

software component.

Figure 11: Parallel Port

12

Pin Configuration

In parallel port, all 8 bits of a byte will be sent to the port at a time and an indication

will be sent in another line. For the accomplishment of this task, the 25 pins are grouped to various groups to accomplish the parts of this task. The below given figure

illustrates it better.

Figure 12: Parallel port configuration

For the above figure, it is clear that the port is composed of 4 control lines, 5 status

lines and 8 data lines and the rest of pins are for ground. The data lines send the data

from port to the external device. Status lines give the information about the current

status of the port and control lines control the port access. The control lines and status

lines are uni-directional i.e. they can feed data only into one direction, whereas the

data ports are bi-directional.

Under our project, the port pins are used for respective purposes:

Table 3: Port pins in our project

Brief Description on parallel port setup

The data pins connected to the rows of the LED matrix (D0 to D4) are used to send

data to the Led Matrix. D0 is connected to the lowest row, D1 is connected to the row

above the one connected to D0 and so on.

D5 data pin is connected to the CP0 of the counter. This pin thus provides the

necessary clock pulse to the counter.

Register Pin No. Connected to

D0 to D4 2 to 6 Each row of the LED matrix starting from the bottom row.

D5 7 CP0 (CLK) of counter

D6 8 MR(Master Reset) of counter

D7 9 Clock to D Flip flops

S6 10 Any one counter output connected to a column.

GND 18 to 25 Ground

13

D6 data pin controls the Master Reset pin of the counter. This pin when high resets the

counter to its starting condition irrespective of its present state.

D7 data pin provides the clock pulses to the D flip flops which are used in the product

for code protection of the LED Matrix. This is further discussed in the sections to be

followed

S6 status pin is used to detect an output pin of a counter which is connected to a

column of the matrix. This status pin is used to determine the number of columns of

the matrix.

Pins 18 to 25 are shorted internally to provide a complete circuit for other pins. Thus

they are used as ground for the parallel port.

Besides these other pins are not used in the project.

Port address For the programming, we require the address of the registers present in port. Usually,

the port address starts with 0x378 in most of the computers. The addresses are in

hexadecimal number system. The addresses for the different registers are given

below.

Registers Address

Data (+0) 0x378

Status (+1) 0x379

Control (+2) 0x379A

Table 4: Address of registers

Parallel Port protection Parallel Port protection is necessary since it can supply and sink very limited amount

of current. A little high current above certain limit may damage the parallel port. In

our case parallel port protection is done using the buffer IC 74244.

Figure 13: IC 74244

2.2 Computer Program A C program was used to create a user interface program to control the parallel port.

The two functions used to control the parallel ports are:

outportb(PORT ADD,Data); (Sends one byte of data)

inportb(PORT ADD,Data); (Reads one byte of data)

14

CHAPTER 3

SYSTEM ANALYSIS AND EXPERIMENTS

3.1 System Analysis

3.1.1 System Analysis

Figure 14: Block Diagram

The LED Matrix display has rows and columns connected separately in order to

reduce the control bits. The rows are connected via transistors, used as switch, to the

parallel port. So the rows of the matrix are controlled by the computer. Similarly the

columns of the matrix are connected via transistors, used as switch, to the counter.

Therefore, the columns are controlled by the counter. The counter consists of 3

cascaded 4017 with 23 working output pins. Therefore, the cascaded counter is used

to produce 23 bits ring counter. In order to display certain character, it is necessary to

synchronize the counter triggering and data sent via parallel port. A certain

combination of data is sent through the port and displayed on first column. When

another bit combination is sent it is necessary to trigger the counter so that the bit

pattern is displayed on second column and so on.

A particular problem may arise when the computer is restarted. Whenever a computer

is restarted, the BIOS sends high bits to all parallel port pins. This may cause a

problem to the LED matrix since the first column is lit at this condition. In order to

prevent this we have designed a circuit which we have named code protection. In this

method we have used two D flipflops whose outputs are Anded and given to a master

transistor switch which acts as a switch to the whole Matrix. Now a certain bit pattern

to clock input and D input of the D FFs will only set the transistor. Therefore, a

particular bit pattern which acts as a code will only initialize the LED Matrix and

prevent unnecessary lighting of the matrix.

Computer Control

Counter

LED Matrix Display

Control Column

Con

trol

Row

Power Flow

Signal Flow

15

3.1.2 Overall description of the circuit

In this section, description and working of the entire circuit is provided. The

description is done in separate parts of each major components of the circuit.

Counter:

4017BD_5V

O0 3

O1 2

O2 4

O3 7

~CP113

MR15

CP014

O4 10

O5 1

O6 5

O7 6

O8 9

O9 11

~O5-9 12

4017BD_5V

O0 3

O1 2

O2 4

O3 7

~CP113

MR15

CP014

O4 10

O5 1

O6 5

O7 6

O8 9

O9 11

~O5-9 12

4017BD_5V

O0 3

O1 2

O2 4

O3 7

~CP113

MR15

CP014

O4 10

O5 1

O6 5

O7 6

O8 9

O9 11

~O5-9 12

CLOCK Figure 15: Cascade Counter Implementation

In cascading, the first decoded output of 1st IC resets the second 4017 IC and so on.

Similarly, the last decoded output of the IC is ANDed with the master clock. Hence,

the second IC gets clock as soon as the last decoded output of first IC is high. Since

we have used 4 LED Matrix we require 23 output counter bits. So 9 bits are taken

from first counter, 8 bits from second counter and 6 bits from third counter. Therefore

the master reset of first counter is connected to output 7 of third counter. Therefore we

have 23 bits output counter.

The clock input the counter is given via the parallel port. Also, the Master Pin is also

connected to the parallel port in addition to output 7 of third column.

16

LED Matrix display

.....

.....

.....

.....

VCC

5V

R0

R1

R2

R3

R4

.....

LED MATRIX SWITCH

O1 O2O0 O4 O5O3 O7 O8O6 O9

To Counter Ouputs

Figure 16: Cascaded LED Matrix

The transistors connected to the buffer IC control the Vcc supply to the LEDs.

Similarly the transistors connected to the counter control the ground to the LEDs.

Furthermore, the anodes of LEDs in a particular row are connected together to a

single transistor controlled by parallel port. Similarly, the cathodes of LEDs in a

particular column are connected together to a single transistor controlled by the

counter. Therefore, we have a setup where we can control any particular row and

column which was our objective.

In order to display a certain character we need to synchronize the triggering of counter

and the data sent through the parallel port. When a certain bit pattern is supplied one

of the columns is lit. Now before the next pattern is supplied it is necessary to trigger

the counter so that next column is initiated. Therefore when the next bit pattern

arrives it is displayed on next column and so on. In order to synchronize the counter

and the parallel port, the clock pulse to the counter is taken from the computer itself

and not by external timer.

The Master LED Matrix switch is used in order to control the entire LED Matrix

Display. This is used in the code protection component which is described in the

following section.

To P

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Port

via

Buff

er I

C

17

Code protection

The code protection is used in order to prevent unnecessary switching on of the LED

Matrix Display. One such condition arises when computer is restated. Similarly when

operating software is loaded the parallel port may have unpredictable bit patterns.

Furthermore, certain noise voltages may also initialize the LED Matrix. So, it is of

prime importance that a design be made to prevent unnecessary lighting up of the

LED Matrix Display. The design used for this purpose in our product is illustrated

below:

D_FF

D Q

~Q

RESET

CLK

SET

D_FF

D Q

~Q

RESET

CLK

SET

Master LED Matrix Transistor

1211

10

9

8

7

LED MATRIX

VCC5V

0

From data pin 7

From data pin 8 Figure17: Code Protection circuit

In order to initialize the LED Matrix we need to supply logic 1 to data pin 7 and clock

pulse to data pin 8 so that both FFs have high outputs. At this condition the transistor

is on and the LED Matrix display has ground supply. Similarly in order to disable the

LED Matrix display, we need to supply logic 0 to data pin 7 and clock pulse to data

pin 8 so that any one of the FFs has 0 output. At this condition the transistor is off and

the LED Matrix is relinquished from ground supply.

When the LED matrix is in working condition, i.e. when characters are being

displayed, the data pin 8 is at 0 pin all the time. Therefore there is no clock pulse to

the D FFs and they are not affected. In this way we can control the entire LED Matrix

Display at any time.

18

3.1.3 Computer Program: Considerable time in the course of this project work has been dedicated to the construction of

a computer program to control the outputs of LED Matrix display. We have constructed a C

program to control the LED Matrix. The features of our program are listed below:

1. Real-Time Display: Allows user to display characters on the matrix display

in real time.

2. Scrolling Display: Allows user to scroll the characters on the matrix display.

3. Automatic detection of number of columns: A status feedback discussed

above detects the number of columns automatically. This also detects if the

hardware is turned on or not. It also follows that the program supports any

number of columns as long as it can maintain a good clock frequency for

persistence of vision.

4. Flexibility: The program is flexible in terms of variations. Any variation such

as modifications to font style can be easily achieved.

5. Alphanumeric characters: Allows user to enter uppercase alphabets (A to

Z) and numerals (0 to 9) along with few special characters (+, -, =).

Functions used in the program and their descriptions:

int essentials() : Determines and Sets pre-requisites of the program

void det_col(): Determines number of columns

void det_mat(): Determines number of matrices

void initials(): Sets default characters

void real_time_disp() : Real-Time Display

int real_time_screen(int *chlen): Real-Time's Menu Screen

int scroll_disp(): Scrolling Display

int scroll_screen(): Scrolling's Menu Screen

void char_select(char tempch[],int strno): Selects entered characters and determines the

bit pattern

void extract(int *bit[],int chlen): Extracts the bit patterns and stores them separately

void byte_dec(int *bit[], int dec[]): Generates decimal equivalence of the extracted bits

sequentially

void real_matrix(int dec[]): Sends data to data port

void initmat(): Enables LED Matrix display

void stopmat(): Disables LED Matrix display

19

Flowchart of the program:

Figure 18: Flowchart of the program

START

Menu

Choice

Call essentials()

Call det_col()

Column

Detected

?

Try

Again

?

Call det_mat()

Check

Menu

Choice

Call real_time_disp() Call scroll_disp()

Call real_time_screen() Call scroll_screen()

Call char_select()

Call extract()

Call byte_dec()

Call real_matrix()

STOP 1 or 2

Esc

YES

NO NO

YES

1 2

Call initmat()

Call stopmat()

20

Flowchart to detect the column of the matrix:

The status line is connected to one of the counter outputs which is connected to one of

the columns. When the output pin is high status becomes low. This initiates the

counting sequence and it continues until the next state when status is again 0.

START

Status

=

0?

Status = 1

Count=Count+1

Status

=

0?

Column = Count

STOP

Clock Pulse

Clock Pulse

YES

NO

YES

NO

Figure 19: Flowchart to detect the columns of the matrix

21

3.2 Mathematical Calculations and Experiments

We have performed several mathematical calculations and experiments under this

project in order to achieve correct outcomes. These calculations and experiments

include:

3.2.1 Mathematical Calculations (All detail calculations are shown in Appendix A)

1. Required instantaneous current for maximum brightness = 0.2A

2. Calculation for Resistors i. For LED Matrix resistors

1

2

0

3

4

6Counter

Port viabuffer

VCC5V

2V

3.1V

5

VCC

RC

RB1

RB2

8

0

Figure 20: LED Matrix component setup

RC = 15

RB1 = 333

RB2 = 2.2k

ii. For Master Led Matrix transistor


LED MATRIX

VCC5V

0

1RB

Figure 21: Master Transistor switch setup

RB = 645

22

3.2.2 Experimental Observations

Experiment 1: Output Pins of Parallel Port and Buffer IC

Direct Port: 5.15V

Corresponding Buffer Output: 6.1V

Experiment 2: Voltage Drop across Diode (Red)

Voltage Drop: 1.81V 2V

Experiment 3: Frequency from the parallel port when data is sent

From Data Pin 6 (Clock input):

Figure 22: Output waveform from data pin 6

Frequency observed: 1.515kHz.

23

From Data Pin 1 (Controls Row 1 of LED Matrix):

Figure 23: Output waveform from data pin 1

Of any particular column

On time 600us Total time period 14ms

24

CHAPTER 4

PRODUCT DESCRIPTION AND PERFORMANCE

4.1 Product Description

4.1.1 Physical Description

The main purpose of this project LED Matrix Display is to display the alphanumeric characters. It is used as a basic way of visual information. These are

best used to advertise, display news on streets, malls, buildings, parks and other

public places. However our product is designed for small purposes such as calculators

and games.

The final product consists of LEDs arranged into 2 dimensional, 55 matrix. There

are 4 such matrices with three additional columns, a D25 male connector for

connection between the parallel port of pc and the display device, LED Matrix

Display.

Figure 24: LED Matrix Display in PCB

Feature of LED Matrix Display

The final product of LED Matrix display can be divided into two parts: They are:

Hardware part and software part.

Hardware part

Code protection: The code protection feature prevents unwanted lighting of the LED

Matrix under certain conditions such as computer restart and noise.

This therefore ensures safety of LEDs.

Maintenance of constant current in the LEDs: The constant current is maintained in each LEDs of the LED Matrix,

Hence this provides equal brightness of LEDs when it is on.

Absence of high level circuits: The circuit is build up by using simple electronic components like

transistors and counter ICs. Advanced components such as

microcontrollers which are usually used to construct LED Matrix

display are not used. Hence, this feature helps to reduce the price of

our final product.

25

Software part

Real-Time Display:

Allows user to display characters on the matrix display in real time.

Scrolling Display:

Allows user to scroll the characters on the matrix display.

Automatic detection of number of columns:

The computer program detects the number of columns automatically. This

also detects if the hardware is turned on or not. Similarly it indicates if the

parallel port is connected or not. It also follows that the program supports any

number of columns as long as it can maintain a good clock frequency for

persistence of vision.

Flexibility:

The program is flexible in terms of variations. Any variation such as

modifications to font style can be easily achieved.

Alphanumeric characters: Allows user to enter uppercase alphabets (A to Z) and numerals (0 to

9) along with few special characters (+, -, =).

26

4.1.2 Cost Estimation

Cost Estimation of LED Matrix Display

Hardware Cost

Item Quantity Rate Price (Rs.)

LEDs 150 1.5 225

Transistor (BC548) 29 4 116

Transistor (SL100) 1 20 20

IC 74244 1 65 65

IC 4017 5 40 200

IC 7408 1 30 30

IC 74244 Holder 1 30 30

IC 4017 Holder 5 10 50

IC 7408 Holder 1 10 10

Zener Diode 5 5 25

Resistor (2.2k) 23 1 23

Resistor (10) 5 1 5

Resistor (300K) 5 1 5

Resistor (450) 3 1 3

Resistor (3.3K) 1 1 1

PCB Board (66) 1 300 300

TOTAL Rs. 1108

Table 5: Cost Estimation

Software Cost

LED Matrix Software = Rs.2500

Labour Cost

Labour cost per hour = Rs. 8

Total hour worked per week = 6 hours

Labour cost per week = Rs. (86) = Rs. 48

Labour cost per month = Rs. (484) = Rs. 192

TOTAL LABOUR COST of 8 months = Rs. (1928) = Rs. 1536

TOTAL COST without profit = Rs. (1108+2500+1536) = Rs. 5144

Profit

5% profit = Rs. 257.2

TOTAL COST with profit = Rs. (5144+257.2) = Rs. 5401.2

27

4.2 Product Performance

Algorithm

1. Connect the parallel port cable to parallel port of the computer. 2. Give 5V DC supply to the circuit. 3. Run the program and follow the menu instructions.

When the above procedure was followed the LED Matrix display worked properly.

The LEDs were lit with constant brightness and the Matrix did not turn on in

unwanted conditions.

4.3 Final Product.

Figure25: Final Product

28

CHAPTER 5

DISCUSSION AND CONCLUSION

The final product of our project has been done on a PCB board. The final product

represents the design concept of our product. The same concept can be utilized to

construct other LED Matrix displays for other purposes such as calculators and LED

Matrix display game.

We have tried to make our product better in every possible way. For this we have

spent considerable time and put on a lot of effort on it. In the course of the

construction of the LED Matrix display we feel that we have achieved much

knowledge and acquired immense experience.

The following is the list of work accomplished during the project course:

Work accomplished:

- Literature survey on existing LED matrix displays and related materials.

- Designing a proper LED Matrix display circuit most appropriate for our purpose.

- Creating a C program to enable user interface between the hardware and the

computer.

- Fabrication of the circuit on a PCB board.

Though we have tried to make the product as complete as possible there is always

room for improvements. The major improvement that can be done in the software

portion is constructing a proper delay function to ensure proper frequency. In our case

we have devised a proper way to maintain appropriate frequency which however can

be computer dependent. When a proper delay function is devised one can also create a

program which can set the on-time and off-time automatically to set proper frequency

automatically for any number of columns. In further improvements, the C program

can be made compatible for Windows NT and higher systems. In hardware portions

suitable parallel port slot and dc supply slot can be created to make the product

portable.

Therefore considering all the facts discussed in this report, it can be assured that our

product works properly and is reliable. The product is quite unique in the sense that

the design concept is in many ways different from that of existing LED Matrix

displays. Thus in the allocated time we have successfully completed our project work

and come up with a fine product.

29

5.1 Gantt Chart

March April May June

Proposal

writing

Proposal

defense

Literature

review

Prototype

design

Testing and

Implementation

Final

presentation

Figure 25: Gantt chart

Work Remaining

Work Completed

30

Bibliography

Boylestad, Robert L & Nashelsky, Louis. Electronic Devices and Circuit Theory. 9th edition. Prentice Hall. India. 2008

http://en.wikipedia.org/wiki/Led http://www.doctronics.co.uk/4017.htm http://electrosofts.com/parallel/parallelwin.html http://logix4u.net/Legacy_Ports/Parallel_Port/A_tutorial_on_Parallel_port_Int

erfacing.html

31

APPENDIX A

MATHEMATICAL CALCULATIONS

1. Calculation for required instantaneous current for maximum brightness

Iav =

Since Iav = =8mA

Iins = =0.18A =0.2A

2. Calculation for Resistors

(i) For LED Matrix resistors

1

2

0

3

4

6Counter

Port viabuffer

VCC5V

2V

3.1V

5

VCC

RC

RB1

RB2

8

0

We have, Isat = 0.2A

Now,

RC = =15

IB1 = = =5.210-4

A

V

600us

14ms

t

32

We take IB1, slightly greater

i.e. IB1 =610-4

A

Now,

RB1 = =333.33

So, we have used 310 resistor.

Similar for RB2,

RB2 = =2.6k 2.2k

(ii) For Master LED Matrix transistor


LED MATRIX

VCC5V

0

1RB

ICsat =0.25 =1A

IB1 = =6.6710-3

A

Therefore, RB = =645

33

APPENDIX B

COMPUTER PROGRAM

/*LED MATRIX DISPLAY PROGRAM FOR MATRIX OF 5 ROWS*/

#include

#include

#include

#include

#include

#include

#include

#define PORT 0x378 /* PORT'S REGISTER ADDRESS */

#define ON_TIME 1

#define OFF_TIME 0

#define ROW 5

int **byte; /* Stores character patterns */

char check; /* Checks choice in menu */

int COL; /* No. of columns */

int MAT; /* No. of matrices */

int charlen=100; /* Maximum number of characters */

char ch[100];

int essentials(); /* Determines and Sets pre-requisites of the program */

void det_col(); /* Determines number of columns */

void det_mat(); /* Determines number of matrices */

void initials(); /* Sets default characters */

void real_time_disp() ; /* Real-Time Display */

int real_time_screen(int *chlen); /* Real-Time's Menu Screen */

int scroll_disp(); /* Scrolling Display */

int scroll_screen(); /* Scrolling's Menu Screen */

void char_select(char tempch[],int strno); /* Selects entered characters and

determines the bit patterns */

void extract(int *bit[],int chlen); /* Extracts the bit patterns and stores

them seperately */

void byte_dec(int *bit[], int dec[]); /* Generates decimal equivalence of the

extracted bits sequentially*/

void real_matrix(int dec[]); /* Sends data to data port */

void initmat(); /* Enables LED Matrix */

void stopmat(); /* Disables LED Matrix */

34

int main(){

while(1){

clrscr();

gotoxy(30,20);

printf("Please enter a choice:\n");

gotoxy(31,22);

printf("1: Real Time Display\n");

gotoxy(31,24);

printf("2: Scrolling Display\n");

gotoxy(36,28);

printf("Esc: Exit:\n\n");

gotoxy(40,30);

check=getch();

delay(100);

if(check=='\033') return 0;

if(essentials()==0) continue;

initmat();

if(check=='1') real_time_disp();

if(check=='2') scroll_disp();

stopmat();

outportb(PORT,0);

}

outportb(PORT,0);

free(ch);

free(byte);

return 0;

}

void initmat(){

outportb(PORT,0);

outportb(PORT,64);

delay(10);

outportb(PORT,192);

delay(10);

outportb(PORT,64);

delay(10);

outportb(PORT,192);

delay(10);

outportb(PORT,64);

delay(10);

outportb(PORT,0);

}

35

void stopmat(){

outportb(PORT,0);

outportb(PORT,0);

delay(10);

outportb(PORT,128);

delay(10);

outportb(PORT,0);

delay(10);

outportb(PORT,128);

delay(10);

outportb(PORT,0);

delay(10);

outportb(PORT,128);

}

int essentials(){

int i;

char chtry;

while(1){

det_col();

if(COL==-1){ /* Column not detected */

clrscr();

gotoxy(33,20);

printf("Column not detected\n");

gotoxy(24,23);

printf("Please check the connection and try again");

gotoxy(30,28);

printf("Press any key to try again");

gotoxy(29,30);

printf("Press Esc to return to menu");

gotoxy(42,32);

chtry=getch();

if (chtry=='\033') return 0;

else continue;

}

det_mat();

initials();

byte=(int *)malloc(charlen*sizeof(int*));/*Create memory to store bit

patterns*/

for(i=0;i

36

void det_col(){

int counter,count=0,checker=0;

int F=0;

int data;

clrscr();

while(1){

checker++; /* Sets the time limit for the counting sequence */

data=inportb(PORT+1);

counter=(data & 0x40)/0x40;/* Checks the status line connected to a counter

output */

gotoxy(38,25);

printf("LOADING");

if(counter==0){ /* Initiate counting sequence */

while(1){

checker=0;

outportb(PORT,32); /* Clock Pulse for the counter */

delay(1);

outportb(PORT,0);

delay(1);

data=inportb(PORT+1);

counter=(data & 0x40)/0x40;

count++; /* Incremented with every timing pulse */

if(counter==0){ /* The counting is stopped */

F=1;

break;

}

}

}

outportb(PORT,32); /* Clock Pulse for the counter */

delay(1);

outportb(PORT,0);

delay(1);

if(F==1) break;

if(checker==1000){ /* If no status detection till checker limit

hardware error */

count=-1;

break;

}

}

COL=count;

outportb(PORT,0);

}

37

void det_mat(){

int m,r;

m=COL/5;

r=COL%5;

if(r!=m-1) m=m-1; /* Sets the most feasible matrix number */

MAT=m;

clrscr();

printf("Column=%d Matrix=%d",COL,MAT);

getch();

}

void initials(){

int i;

for(i=0;i

38

value=real_time_screen(&i);

if(value==0) break; /* Esc or Enter Pressed */

if(value==-1) continue; /* Maximum character reached */

k=i;

gotoxy(20,20);

if(i0){ /* Backspace */

if(i=charlen-1){ /* Maximum character check */

gotoxy(26,15);

printf("Maximum character limit reached");

gotoxy(xco,yco);

return -1;

}

if((ch[i]>=060&&ch[i]=0101&&ch[i]

39

i++;

*chlen=i;

return 1;

}

return -1;

}

int scroll_disp(){

int i=0,j,x=40;

int xco,yco;

int col=0;

float check=0;

int shift;

int start=COL,add=0;

float scroll_speed;

int swap_shift=0;

int chlen;

int *bit[ROW],*temp[ROW];

int *dec;

char keystr,tempch;

dec=(int *)malloc(COL*sizeof(int));

for(i=0;i

40

if(check>scroll_speed) check=scroll_speed-1;

gotoxy(5,5);

//printf("%d ",scroll_speed);

}

gotoxy(25,25);

cprintf("");

gotoxy(x,25);

cprintf("|");

gotoxy(40,26);

printf("%f %f",scroll_speed,check);

check++;

byte_dec(temp,dec);

real_matrix(dec);

if(check>scroll_speed){ /* Change pattern of output */

shift--;

check=0;

if(swap_shift==0){ /* Scroll the characters to the left */

start--;

if(start

41

}

}

}

}

return 0;

}

int scroll_screen(){

int i=0;

char tempch;

int xco,yco,init_yco;

clrscr();

gotoxy(26,1);

printf("LED MATRIX SCROLLING DISPLAY");

gotoxy(1,6);

printf("PLEASE ENTER THE CHARACTER SEQUENCE: ");

init_yco=wherey();

while(1){ /* To compensate the

problem with getch() */

xco=wherex();

yco=wherey();

if(i>charlen){ /* Maximum character

reached */

gotoxy(25,10);

printf("Maximum character limit reached");

gotoxy(xco,yco);

}

else{

gotoxy(24,10);

printf(" ");

gotoxy(xco,yco);

}

tempch=toupper(getch());

if(tempch=='\015'||tempch=='\033') break; /* If Enter or Esc */

if(tempch=='\010'){ /* If Backspace */

if(i>0){

ch[i]='\000';

i--;

if(wherey()!=init_yco&&wherex()==1) gotoxy(80,wherey()-1);

else gotoxy(wherex()-1,wherey());

clreol();

}

continue;

}

if(i>charlen) continue;

if((tempch>=060&&tempch=0101&&tempch

42

i++;

}

}

gotoxy(24,10);

printf(" ");

gotoxy(24,15);

printf("PRESS:\n");

gotoxy(27,17);

printf("+ : Increase scrolling speed");

gotoxy(27,19);

printf("- : Decrease scrolling speed");

gotoxy(28,40);

printf("Press Esc to return to menu");

if(i==0){

ch[0]=' ';

return 1;

}

else return i;

}

void extract(int *bit[],int chlen){

int i,j,k,l,r,q;

for(i=0;i=0;j--){ /* Start from the last character */

q=byte[j][i];

for(k=0;k

43

void real_matrix(int dec[]){

int i;

float j=0;

outportb(PORT,64); /* Master Reset */

for(i=0;i

44

byte[i][0]=10001;

byte[i][1]=10001;

byte[i][2]=11111;

byte[i][3]=1;

byte[i][4]=1;

break;

case '5':

byte[i][0]=11111;

byte[i][1]=10000;

byte[i][2]=11110;

byte[i][3]=1;

byte[i][4]=11110;

break;

case '6':

byte[i][0]=1110;

byte[i][1]=10000;

byte[i][2]=11110;

byte[i][3]=10001;

byte[i][4]=1110;

break;

case '7':

byte[i][0]=11111;

byte[i][1]=1;

byte[i][2]=10;

byte[i][3]=100;

byte[i][4]=1000;

break;

case '8':

byte[i][0]=1110;

byte[i][1]=10001;

byte[i][2]=1110;

byte[i][3]=10001;

byte[i][4]=1110;

break;

case '9':

byte[i][0]=1110;

byte[i][1]=10001;

byte[i][2]=1111;

byte[i][3]=1;

byte[i][4]=1110;

break;

case 'A':

byte[i][0]=1110;

byte[i][1]=10001;

byte[i][2]=11111;

byte[i][3]=10001;

byte[i][4]=10001;

break;

case 'B':

45

byte[i][0]=11110;

byte[i][1]=10001;

byte[i][2]=11110;

byte[i][3]=10001;

byte[i][4]=11110;

break;

case 'C':

byte[i][0]=1111;

byte[i][1]=10000;

byte[i][2]=10000;

byte[i][3]=10000;

byte[i][4]=1111;

break;

case 'D':

byte[i][0]=11110;

byte[i][1]=10001;

byte[i][2]=10001;

byte[i][3]=10001;

byte[i][4]=11110;

break;

case 'E':

byte[i][0]=11111;

byte[i][1]=10000;

byte[i][2]=11110;

byte[i][3]=10000;

byte[i][4]=11111;

break;

case 'F':

byte[i][0]=11111;

byte[i][1]=10000;

byte[i][2]=11110;

byte[i][3]=10000;

byte[i][4]=10000;

break;

case 'G':

byte[i][0]=11111;

byte[i][1]=10000;

byte[i][2]=10111;

byte[i][3]=10101;

byte[i][4]=11101;

break;

case 'H':

byte[i][0]=10001;

byte[i][1]=10001;

byte[i][2]=11111;

byte[i][3]=10001;

byte[i][4]=10001;

break;

case 'I':

byte[i][0]=11111;

46

byte[i][1]=100;

byte[i][2]=100;

byte[i][3]=100;

byte[i][4]=11111;

break;

case 'J':

byte[i][0]=1111;

byte[i][1]=10;

byte[i][2]=10;

byte[i][3]=10010;

byte[i][4]=1100;

break;

case 'K':

byte[i][0]=10011;

byte[i][1]=10100;

byte[i][2]=11000;

byte[i][3]=10100;

byte[i][4]=10011;

break;

case 'L':

byte[i][0]=10000;

byte[i][1]=10000;

byte[i][2]=10000;

byte[i][3]=10000;

byte[i][4]=11111;

break;

case 'M':

byte[i][0]=10001;

byte[i][1]=11011;

byte[i][2]=10101;

byte[i][3]=10001;

byte[i][4]=10001;

break;

case 'N':

byte[i][0]=10001;

byte[i][1]=11001;

byte[i][2]=10101;

byte[i][3]=10011;

byte[i][4]=10001;

break;

case 'O':

byte[i][0]=1110;

byte[i][1]=10001;

byte[i][2]=10001;

byte[i][3]=10001;

byte[i][4]=1110;

break;

case 'P':

byte[i][0]=11110;

byte[i][1]=10001;

47

byte[i][2]=11110;

byte[i][3]=10000;

byte[i][4]=10000;

break;

case 'Q':

byte[i][0]=1110;

byte[i][1]=10001;

byte[i][2]=10101;

byte[i][3]=10011;

byte[i][4]=1111;

break;

case 'R':

byte[i][0]=11110;

byte[i][1]=10001;

byte[i][2]=11110;

byte[i][3]=10100;

byte[i][4]=10011;

break;

case 'S':

byte[i][0]=1111;

byte[i][1]=10000;

byte[i][2]=11110;

byte[i][3]=1;

byte[i][4]=11110;

break;

case 'T':

byte[i][0]=11111;

byte[i][1]=100;

byte[i][2]=100;

byte[i][3]=100;

byte[i][4]=100;

break;

case 'U':

byte[i][0]=10001;

byte[i][1]=10001;

byte[i][2]=10001;

byte[i][3]=10001;

byte[i][4]=1110;

break;

case 'V':

byte[i][0]=10001;

byte[i][1]=10001;

byte[i][2]=10001;

byte[i][3]=1010;

byte[i][4]=100;

break;

case 'W':

byte[i][0]=10001;

byte[i][1]=10001;

byte[i][2]=10101;

48

byte[i][3]=11011;

byte[i][4]=10001;

break;

case 'X':

byte[i][0]=10001;

byte[i][1]=1010;

byte[i][2]=100;

byte[i][3]=1010;

byte[i][4]=10001;

break;

case 'Y':

byte[i][0]=10001;

byte[i][1]=1010;

byte[i][2]=100;

byte[i][3]=100;

byte[i][4]=100;

break;

case 'Z':

byte[i][0]=11111;

byte[i][1]=10;

byte[i][2]=100;

byte[i][3]=1000;

byte[i][4]=11111;

break;

case '`':

byte[i][0]=11111;

byte[i][1]=11111;

byte[i][2]=11111;

byte[i][3]=11111;

byte[i][4]=11111;

break;

case '-':

byte[i][0]=0;

byte[i][1]=0;

byte[i][2]=11111;

byte[i][3]=0;

byte[i][4]=0;

break;

case '+':

byte[i][0]=100;

byte[i][1]=100;

byte[i][2]=11111;

byte[i][3]=100;

byte[i][4]=100;

break;

case '=':

byte[i][0]=0;

byte[i][1]=11111;

byte[i][2]=0;

byte[i][3]=11111;

49

byte[i][4]=0;

break;

case '^':

byte[i][0]=100;

byte[i][1]=1010;

byte[i][2]=10001;

byte[i][3]=0;

byte[i][4]=0;

break;

default:

byte[i][0]=0;

byte[i][1]=0;

byte[i][2]=0;

byte[i][3]=0;

byte[i][4]=0;

}

}

}

50

APPENDIX C

PCB Circuit

Top section

51

Bottom section

52

APPENDIX D

DATASHEETS

The following pages contain datasheets of the components used in the final product.

The datasheets are organized sequentially in following order:

1. Datasheet of BC548 2. Datasheet of 1N4148 3. Datasheet of SL100 4. Datasheet of 74244 5. Datasheet of 7408 6. Datasheet of 74175 7. Datasheet of 4017

BC548 / BC548A / BC548B / BC548C

NPN General Purpose Amplifier

BC548BC548ABC548BBC548C

This device is designed for use as general purpose amplifiersand switches requiring collector currents to 300 mA. Sourced fromProcess 10. See PN100A for characteristics.

Absolute Maximum Ratings* TA = 25C unless otherwise noted

*These ratings are limiting values above which the serviceability of any semiconductor device may be impaired.

NOTES:1) These ratings are based on a maximum junction temperature of 150 degrees C.2) These are steady state limits. The factory should be consulted on applications involving pulsed or low duty cycle operations.

Thermal Characteristics TA = 25C unless otherwise noted

Symbol Parameter Value UnitsVCEO Collector-Emitter Voltage 30 VVCES Collector-Base Voltage 30 VVEBO Emitter-Base Voltage 5.0 VIC Collector Current - Continuous 500 mATJ, Tstg Operating and Storage Junction Temperature Range -55 to +150 C

Symbol Characteristic Max UnitsBC548 / A / B / C

PD Total Device DissipationDerate above 25C

6255.0

mWmW/C

RJC Thermal Resistance, Junction to Case 83.3 C/WRJA Thermal Resistance, Junction to Ambient 200 C/W

EB C

TO-92

1997 Fairchild Semiconductor Corporation 548-ABC, Rev B

BC548 / BC548A / BC548B / BC548CNPN General Purpose Amplifier

(continued)

Electrical Characteristics TA = 25C unless otherwise noted

OFF CHARACTERISTICS

Symbol Parameter Test Conditions Min Max Units

V(BR)CEO Collector-Emitter Breakdown Voltage IC = 10 mA, IB = 0 30 VV(BR)CBO Collector-Base Breakdown Voltage IC = 10 A, IE = 0 30 VV(BR)CES Collector-Base Breakdown Voltage IC = 10 A, IE = 0 30 VV(BR)EBO Emitter-Base Breakdown Voltage IE = 10 A, IC = 0 5.0 VICBO Collector Cutoff Current VCB = 30 V, IE = 0

VCB = 30 V, IE = 0, TA = +150 C155.0

nAA

ON CHARACTERISTICShFE DC Current Gain VCE = 5.0 V, IC = 2.0 mA 548

548A 548B

548C

110110200420

800220450800

VCE(sat) Collector-Emitter Saturation Voltage IC = 10 mA, IB = 0.5 mAIC = 100 mA, IB = 5.0 mA

0.250.60

VV

VBE(on) Base-Emitter On Voltage VCE = 5.0 V, IC = 2.0 mAVCE = 5.0 V, IC = 10 mA

0.58 0.700.77

VV

SMALL SIGNAL CHARACTERISTICShfe Small-Signal Current Gain IC = 2.0 mA, VCE = 5.0 V,

f = 1.0 kHz125 900

NF Noise Figure VCE = 5.0 V, IC = 200 A,RS = 2.0 k, f = 1.0 kHz,BW = 200 Hz

10 dB

DATA SHEET

Product data sheet Supersedes data of 2002 Jan 23

2004 Aug 10

DISCRETE SEMICONDUCTORS

1N4148; 1N4448High-speed diodes

M3D176

NXP Semiconductors Product data sheetTYPE NUMBERPACKAGE

NAME DESCRIPTION VERSION1N4148 hermetically sealed glass package; axial leaded; 2 leads SOD271N4448High-speed diodes 1N4148; 1N4448

FEATURES

Hermetically sealed leaded glass SOD27 (DO-35) package

High switching speed: max. 4 ns General application Continuous reverse voltage: max. 100 V Repetitive peak reverse voltage: max. 100 V Repetitive peak forward current: max. 450 mA.

APPLICATIONS

High-speed switching.

DESCRIPTION

The 1N4148 and 1N4448 are high-speed switching diodes fabricated in planar technology, and encapsulated in hermetically sealed leaded glass SOD27 (DO-35) packages.

MARKING

TYPE NUMBER MARKING CODE1N4148 1N4148PH or 4148PH1N4448 1N4448

Fig.1 Simplified outline (SOD27; DO-35) and symbol.

The diodes are type branded.

handbook, halfpage

MAM246

k a

ORDERING INFORMATION2004 Aug 10 2

NXP Semiconductors Product data sheetSYMBOL PARAMETER CONDITIONS MIN. MAX. UNITVF forward voltage see Fig.3

1N4148 IF = 10 mA 1 V1N4448 IF = 5 mA 0.62 0.72 V

IF = 100 mA 1 VIR reverse current VR = 20 V; see Fig.5 25 nA

VR = 20 V; Tj = 150 C; see Fig.5 50 AIR reverse current; 1N4448 VR = 20 V; Tj = 100 C; see Fig.5 3 ACd diode capacitance f = 1 MHz; VR = 0 V; see Fig.6 4 pFtrr reverse recovery time when switched from IF = 10 mA to

IR = 60 mA; RL = 100 ; measured at IR = 1 mA; see Fig.7

4 ns

Vfr forward recovery voltage when switched from IF = 50 mA; tr = 20 ns; see Fig.8

2.5 V

THERMAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS VALUE UNITRth(j-tp) thermal resistance from junction to tie-point lead length 10 mm 240 K/WRth(j-a) thermal resistance from junction to ambient lead length 10 mm; note 1 350 K/WNote1. Device mounted on an FR4 printed-circuit board; lead length 10 mm.

VRRM repetitive peak reverse voltage 100 VVR continuous reverse voltage 100 VIF continuous forward current see Fig.2; note 1 200 mAIFRM repetitive peak forward current 450 mAIFSM non-repetitive peak forward current square wave; Tj = 25 C prior to

surge; see Fig.4t = 1 s 4 At = 1 ms 1 At = 1 s 0.5 A

Ptot total power dissipation Tamb = 25 C; note 1 500 mWTstg storage temperature 65 +200 CTj junction temperature 200 C

ELECTRICAL CHARACTERISTICSTj = 25 C unless otherwise specified.High-speed diodes 1N4148; 1N4448

LIMITING VALUESIn accordance with the Absolute Maximum Rating System (IEC 60134).

SYMBOL PARAMETER CONDITIONS MIN. MAX. UNIT2004 Aug 10 3

Note1. Device mounted on a printed-circuit board without metallization pad.

2000 Fairchild Semiconductor Corporation DS008442 www.fairchildsemi.com

August 1986Revised March 2000

DM

74LS244 O

ctal 3-STATE Buffe

r/Line

Drive

r/Line Receiv

er

DM74LS244Octal 3-STATE Buffer/Line Driver/Line ReceiverGeneral DescriptionThese buffers/line drivers are designed to improve both theperformance and PC board density of 3-STATE buffers/drivers employed as memory-address drivers, clock driv-ers, and bus-oriented transmitters/receivers. Featuring 400mV of hysteresis at each low current PNP data line input,they provide improved noise rejection and high fanout out-puts and can be used to drive terminated lines down to133.

Featuresn 3-STATE outputs drive bus lines directlyn PNP inputs reduce DC loading on bus linesn Hysteresis at data inputs improves noise marginsn Typical IOL (sink current) 24 mAn Typical IOH (source current) 15 mAn Typical propagation delay times

Inverting 10.5 nsNoninverting 12 ns

n Typical enable/disable time 18 nsn Typical power dissipation (enabled)

Inverting 130 mWNoninverting 135 mW

Ordering Code:

Devices also available in Tape and Reel. Specify by appending the suffix letter X to the ordering code.

Connection Diagram Function Table

L = LOW Logic LevelH = HIGH Logic LevelX = Either LOW or HIGH Logic LevelZ = High Impedance

Order Number Package Number Package DescriptionDM74LS244WM M20B 20-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300 WideDM74LS244SJ M20D 20-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm WideDM74LS244N N20A 20-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide

Inputs OutputG A YL L LL H HH X Z

www.fairchildsemi.com 2

DM

74LS

244

Absolute Maximum Ratings(Note 1)Note 1: The Absolute Maximum Ratings are those values beyond whichthe safety of the device cannot be guaranteed. The device should not beoperated at these limits. The parametric values defined in the ElectricalCharacteristics tables are not guaranteed at the absolute maximum ratings.The Recommended Operating Conditions table will define the conditionsfor actual device operation.

Recommended Operating Conditions

Electrical Characteristics over recommended operating free air temperature range (unless otherwise noted)

Note 2: All typicals are at VCC = 5V, TA = 25C.Note 3: Not more than one output should be shorted at a time, and the duration should not exceed one second.

Supply Voltage 7VInput Voltage 7VOperating Free Air Temperature Range 0C to +70CStorage Temperature Range 65C to +150C

Symbol Parameter Min Nom Max UnitsVCC Supply Voltage 4.75 5 5.25 VVIH HIGH Level Input Voltage 2 VVIL LOW Level Input Voltage 0.8 VIOH HIGH Level Output Current 15 mAIOL LOW Level Output Current 24 mATA Free Air Operating Temperature 0 70 C

Symbol Parameter Conditions Min Typ Max

Units(Note 2)VI Input Clamp Voltage VCC = Min, II = 18 mA 1.5 VHYS Hysteresis (VT+ VT) VCC = Min 0.2 0.4 V

Data Inputs OnlyVOH HIGH Level Output Voltage VCC = Min, VIH = Min 2.7

VIL = Max, IOH = 1 mAVCC = Min, VIH = Min 2.4 3.4 VVIL = Max, IOH = 3 mAVCC = Min, VIH = Min 2VIL = 0.5V, IOH = Max

VOL LOW Level Output Voltage VCC = Min IOL = 12 mA 0.4VVIL = Max IOL = Max 0.5

VIH = MinIOZH Off-State Output Current, VCC = Max VO = 2.7V 20 A

HIGH Level Voltage Applied VIL = MaxIOZL Off-State Output Current, VIH = Min VO = 0.4V 20 A

LOW Level Voltage AppliedII Input Current at Maximum VCC = Max VI = 7V 0.1 mA

Input VoltageIIH HIGH Level Input Current VCC = Max VI = 2.7V 20 AIIL LOW Level Input Current VCC = Max VI = 0.4V 0.5 200 AIOS Short Circuit Output Current VCC = Max (Note 3) 40 225 mAICC Supply Current VCC = Max, Outputs HIGH 13 23

Outputs Open Outputs LOW 27 46 mAOutputs Disabled 32 54

3 www.fairchildsemi.com

DM

74LS244Switching Characteristics at VCC = 5V, TA = 25C Symbol Parameter Conditions Max Units

tPLH Propagation Delay Time CL = 45 pF 18 nsLOW-to-HIGH Level Output RL = 667

tPHL Propagation Delay Time CL = 45 pF 18 nsHIGH-to-LOW Level Output RL = 667

tPZL Output Enable Time to CL = 45 pF 30 nsLOW Level RL = 667

tPZH Output Enable Time to CL = 45 pF 23 nsHIGH Level RL = 667

tPLZ Output Disable Time CL = 5 pF 25 nsfrom LOW Level RL = 667

tPHZ Output Disable Time CL = 5 pF 18 nsfrom HIGH Level RL = 667

tPLH Propagation Delay Time CL = 150 pF 21 nsLOW-to-HIGH Level Output RL = 667

tPHL Propagation Delay Time CL = 150 pF 22 nsHIGH-to-LOW Level Output RL = 667

tPZL Output Enable Time to CL = 150 pF 33 nsLOW Level RL = 667

tPZH Output Enable Time to CL = 150 pF 26 nsHIGH Level RL = 667

Philips Semiconductors

74F08Quad two-input AND gate

Product specification 1995 Apr 19

INTEGRATED CIRCUITS

IC15 Data Handbook

Philips Semiconductors Product specification

74F08Quad 2-input AND gate

21995 Apr 19 8530328 15145

74F08 Available for industrial range (40C to +85C)

TYPE TYPICALPROPAGATION

DELAY

TYPICALSUPPLY CURRENT

(TOTAL)74F08 4.1ns 7.1mA

PIN CONFIGURATION

14

13

12

11

10

9

87

6

5

4

3

2

1

GND

VCC

D2b

D2a

Q2

Q3

D3b

D3a

D0a

D0b

Q1

Q0

D1a

D1b

SF00038

ORDERING INFORMATION

DESCRIPTION COMMERCIAL RANGEVCC = 5.0V 10%, Tamb = 0C to +70CINDUSTRIAL RANGE

VCC = 5.0V 10%, Tamb = 40C to +85CPKG DWG #

14-pin plastic DIP N74F08N I74F08N SOT27-1

14-pin plastic SO N74F08D I74F08D SOT108-1

INPUT AND OUTPUT LOADING AND FAN-OUT TABLEPINS DESCRIPTION 74F (U.L.) HIGH/LOW LOAD VALUE HIGH/LOW

Dna, Dnb Data inputs 1.0/1.0 20A/0.6mA

Qn Data output 50/33 1.0mA/20mANOTE: One (1.0) FAST unit load is defined as: 20A in the High state and 0.6mA in the Low state.

LOGIC DIAGRAMD0aD0b

D1aD1b

D2a

Q0

D2b

D3aD3b

Q1

Q2

Q3

VCC = Pin 14GND = Pin 7

3

6

8

11

12

45

910

1213

SF00052

FUNCTION TABLEINPUTS OUTPUT

Dna Dnb QnL L LL H LH L LH H H

NOTES:H = High voltage levelL = Low voltage level

LOGIC SYMBOL

D0a D0bD1a D2a D2b D3a D3bD1b

Q0 Q1 Q2 Q3

3 6 8 11

1 2 4 5 9 10 12 13

VCC = Pin 14GND = Pin 7

SF00040

LOGIC SYMBOL (IEEE/IEC)1

2

4

5

9

10

12

13

&3

6

8

11

SF00053

5-1FAST AND LS TTL DATA

QUAD D FLIP-FLOPThe LSTTL/MSI SN54/74LS175 is a high speed Quad D Flip-Flop. The

device is useful for general flip-flop requirements where clock and clear inputsare common. The information on the D inputs is stored during the LOW toHIGH clock transition. Both true and complemented outputs of each flip-flopare provided. A Master Reset input resets all flip-flops, independent of theClock or D inputs, when LOW.

The LS175 is fabricated with the Schottky barrier diode process for highspeed and is completely compatible with all Motorola TTL families. Edge-Triggered D-Type Inputs Buffered-Positive Edge-Triggered Clock Clock to Output Delays of 30 ns Asynchronous Common Reset True and Complement Output Input Clamp Diodes Limit High Speed Termination Effects

NOTE:The Flatpak versionhas the same pinouts(Connection Diagram) asthe Dual In-Line Package.

CONNECTION DIAGRAM DIP (TOP VIEW)

14 13 12 11 10 9

1 2 3 4 5 6 7

16 15

8

VCC

MR

Q3 Q3 D3 D2 Q2Q2 CP

Q0 Q0 D0 D1 Q1 Q1 GND

PIN NAMES LOADING (Note a)HIGH LOW

D0D3CPMRQ0Q3Q0Q3

Data InputsClock (Active HIGH Going Edge) InputMaster Reset (Active LOW) InputTrue Outputs (Note b)Complemented Outputs (Note b)

0.5 U.L.0.5 U.L.0.5 U.L.10 U.L.10 U.L.

0.25 U.L.0.25 U.L.0.25 U.L.

5 (2.5) U.L.5 (2.5) U.L.

NOTES:a. 1 TTL Unit Load (U.L.) = 40 A HIGH/1.6 mA LOW.b. The Output LOW drive factor is 2.5 U.L. for Military (54) and 5 U.L. for Commercial (74)b. Temperature Ranges.

LOGIC DIAGRAM

D Q

CPCD

Q

CP D3 D2 D1 D0

Q3Q3 Q2Q2 Q1Q1 Q0Q0

D Q

CPCD

Q

MR

14

1

26 7 3

459

11

12

10

13

15VCC = PIN 16GND = PIN 8

= PIN NUMBERS

D Q

CPCD

Q

D Q

CPCD

Q

SN54/74LS175

QUAD D FLIP-FLOPLOW POWER SCHOTTKY

J SUFFIXCERAMIC

CASE 620-09

N SUFFIXPLASTIC

CASE 648-08

161

161

ORDERING INFORMATIONSN54LSXXXJ CeramicSN74LSXXXN PlasticSN74LSXXXD SOIC

161

D SUFFIXSOIC

CASE 751B-03

LOGIC SYMBOL

VCC = PIN 16GND = PIN 8

12

1

23 6 7 11 14 1510

4 5 13

9 CPD0 D1 D2 D3

MRQ0 Q0 Q1 Q1 Q2 Q2 Q3 Q3

5-2FAST AND LS TTL DATA

SN54/74LS175

FUNCTIONAL DESCRIPTIONThe LS175 consists of four edge-triggered D flip-flops with

individual D inputs and Q and Q outputs. The Clock andMaster Reset are common. The four flip-flops will store thestate of their individual D inputs on the LOW to HIGH Clock(CP) transition, causing individual Q and Q outputs to follow. A

LOW input on the Master Reset (MR) will force all Q outputsLOW and Q outputs HIGH independent of Clock or Datainputs.

The LS175 is useful for general logic applications where acommon Master Reset and Clock are acceptable.

TRUTH TABLEInputs (t = n, MR = H) Outputs (t = n+1) Note 1

D Q QL L HH H L

Note 1: t = n + 1 indicates conditions after next clock.

GUARANTEED OPERATING RANGESSymbol Parameter Min Typ Max Unit

VCC Supply Voltage 5474

4.54.75

5.05.0

5.55.25

V

TA Operating Ambient Temperature Range 5474

550

2525

12570

C

IOH Output Current High 54, 74 0.4 mA

IOL Output Current Low 5474

4.08.0

mA

DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE (unless otherwise specified)

S b l P

Limits

U i T C di iSymbol Parameter Min Typ Max Unit Test Conditions

VIH Input HIGH Voltage 2.0 VGuaranteed Input HIGH Voltage forAll Inputs

VIL Input LOW Voltage54 0.7

VGuaranteed Input LOW Voltage for

VIL Input LOW Voltage 74 0.8V

p gAll Inputs

VIK Input Clamp Diode Voltage 0.65 1.5 V VCC = MIN, IIN = 18 mA

VOH Output HIGH Voltage54 2.5 3.5 V VCC = MIN, IOH = MAX, VIN = VIHVOH Output HIGH Voltage 74 2.7 3.5 V

CC , OH , IN IHor VIL per Truth Table

VOL Output LOW Voltage54, 74 0.25 0.4 V IOL = 4.0 mA VCC = VCC MIN,

VIN = VIL or VIHVOL Output LOW Voltage74 0.35 0.5 V IOL = 8.0 mA

VIN = VIL or VIHper Truth Table

IIH Input HIGH Current20 A VCC = MAX, VIN = 2.7 V

IIH Input HIGH Current 0.1 mA VCC = MAX, VIN = 7.0 V

IIL Input LOW Current 0.4 mA VCC = MAX, VIN = 0.4 V

IOS Short Circuit Current (Note 1) 20 100 mA VCC = MAXICC Power Supply Current 18 mA VCC = MAX

Note 1: Not more than one output should be shorted at a time, nor for more than 1 second.

DATA SHEET

Product specificationFile under Integrated Circuits, IC04

January 1995

INTEGRATED CIRCUITS

HEF4017BMSI5-stage Johnson counter

For a complete data sheet, please also download:

The IC04 LOCMOS HE4000B LogicFamily Specifications HEF, HEC

The IC04 LOCMOS HE4000B LogicPackage Outlines/Information HEF, HEC

January 1995 2


5-stage Johnson counter HEF4017BMSI

DESCRIPTIONThe HEF4017B is a 5-stage Johnson decade counter withten spike-free decoded active HIGH outputs (Oo to O9), anactive LOW output from the most significant flip-flop (O5-9),active HIGH and active LOW clock inputs (CP0, CP1) andan overriding asynchronous master reset input (MR).The counter is advanced by either a LOW to HIGHtransition at CP0 while CP1 is LOW or a HIGH to LOWtransition at CP1 while CP0 is HIGH (see also functiontable).When cascading counters, the O5-9 output, which is LOWwhile the counter is in states 5, 6, 7, 8 and 9, can be usedto drive the CP0 input of the next counter.

A HIGH on MR resets the counter to zero(Oo = O5-9 = HIGH; O1 to O9 = LOW) independent of theclock inputs (CP0, CP1).Automatic code correction of the counter is provided by aninternal circuit: following any illegal code the counterreturns to a proper counting mode within 11 clock pulses.Schmitt-trigger action in the clock input makes the circuithighly tolerant to slower clock rise and fall times.

Fig.1 Functional diagram.

HEF4017BP(N): 16-lead DIL; plastic (SOT38-1)HEF4017BD(F): 16-lead DIL; ceramic (cerdip) (SOT74)HEF4017BT(D): 16-lead SO; plastic (SOT109-1)( ): Package Designator North America

Fig.2 Pinning diagram.

PINNING

FAMILY DATA, IDD LIMITS category MSI

See Family Specifications

CP0 clock input (LOW to HIGH triggered)CP1 clock input (HIGH to LOW triggered)MR master reset inputO0 to O9 decoded outputsO5-9 carry output (active LOW)

January 19953

Philips Semiconductors

Product specification

5-stage Johnson counterH

EF4017BM

SI

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Fig.3 Logic diagram.

January 1995 4



FUNCTION TABLE

MR CP0 CP1 OPERATIONH X X O0 = O5-9 = H; O1 to O9 = L

L H Counter advances

L L Counter advances

L L X No changeL X H No change

L H No change

L L No change

Notes1. H = HIGH state (the more positive voltage)2. L = LOW state (the less positive voltage)3. X = state is immaterial

4. = positive-going transition

5. = negative-going transition

AC CHARACTERISTICSVSS = 0 V; Tamb = 25 C; CL = 50 pF; input transition times 20 ns

VDDV SYMBOL MIN. TYP. MAX.

TYPICAL EXTRAPOLATIONFORMULA

Propagation delaysCP0, CP1 O0 to O9 5 140 280 ns 113 ns + (0,55 ns/pF) CL

HIGH to LOW 10 tPHL 55 110 ns 44 ns + (0,23 ns/pF) CL15 40 80 ns 32 ns + (0,16 ns/pF) CL

5 125 250 ns 98 ns + (0,55 ns/pF) CLLOW to HIGH 10 tPLH 50 100 ns 39 ns + (0,23 ns/pF) CL

15 40 80 ns 32 ns + (0,16 ns/pF) CLCP0, CP1 O5-9 5 145 290 ns 118 ns + (0,55 ns/pF) CL


5 125 250 ns 98 ns + (0,55 ns/pF) CLLOW to HIGH 10 tPLH 50 100 ns 39 ns + (0,23 ns/pF) CL

15 40 80 ns 32 ns + (0,16 ns/pF) CLMR O1 to O9 5 115 230 ns 88 ns + (0,55 ns/pF) CL


MR O5-9 5 110 220 ns 83 ns + (0,55 ns/pF) CLLOW to HIGH 10 tPLH 45 90 ns 34 ns + (0,23 ns/pF) CL

15 35 70 ns 27 ns + (0,16 ns/pF) CLMR O0 5 130 260 ns 103 ns + (0,55 ns/pF) CL

LOW to HIGH 10 tPLH 55 105 ns 44 ns + (0,23 ns/pF) CL15 40 75 ns 32 ns + (0,16 ns/pF) CL

January 1995 5



AC CHARACTERISTICSVSS = 0 V; Tamb = 25 C; CL = 50 pF; input transition times 20 ns

Output transitiontimes 5 60 120 ns 10 ns + (1,0 ns/pF) CLHIGH to LOW 10 tTHL 30 60 ns 9 ns + (0,42 ns/pF) CL

15 20 40 ns 6 ns + (0,28 ns/pF) CL5 60 120 ns 10 ns + (1,0 ns/pF) CL

LOW to HIGH 10 tTLH 30 60 ns 9 ns + (0,42 ns/pF) CL15 20 40 ns 6 ns + (0,28 ns/pF) CL


Hold times 5 90 45 nsCP0 CP1 10 thold 40 20 ns

15 20 10 ns5 80 40 ns

CP1 CP0 10 thold 40 20 ns15 30 10 ns

Minimum clockpulse width: 5

tWCPL =tWCPH

80 40 nsCP0 = LOW; 10 40 20 ns see also waveformsCP1 = HIGH 15 30 15 ns Figs 4 and 5

Minimum MR 5 50 25 nspulse width; HIGH 10 tWMRH 30 15 ns

15 20 10 nsRecovery time 5 60 30 ns

for MR 10 tRMR 30 15 ns15 20 10 ns

Maximum clock 5 6 12 MHzpulse frequency 10 fmax 12 24 MHz

15 15 30 MHz

VDDV TYPICAL FORMULA FOR P (W)

Dynamic power 5 500 fi + (foCL) VDD2 wheredissipation per 10 2200 fi + (foCL) VDD2 fi = input freq. (MHz)package (P) 15 6000 fi + (foCL) VDD2 fo = output freq. (MHz)

CL = load cap. (pF) (foCL) = sum of outputsVDD = supply voltage (V)


TYPICAL EXTRAPOLATIONFORMULA

January 1995 6



Fig.4 Waveforms showing hold times for CP0 to CP1 and CP1 to CP0. Hold times are shown as positive values,but may be specified as negative values.

Fig.5 Waveforms showing recovery time for MR; minimum CP0 and MR pulse widths.

Conditions: CP1 = LOW while CP0 is triggered on a LOW to HIGH transition. tWCP andtRMR also apply when CP0 = HIGH and CP1 is triggered on a HIGH to LOW transition.

January 1995 7



Fig.6 Timing diagram.

January 1995 8



APPLICATION INFORMATIONSome examples of applications for the HEF4017B are: Decade counter with decimal decoding 1 out of n decoding counter (when cascaded) Sequential controller Timer.

Figure 7 shows a technique for extending the number of decoded output states for the HEF4017B. Decoded outputs aresequential within each stage and from stage to stage, with no dead time (except propagation delay).

Note

It is essential not to enable the counter on CP1 when CP0 is HIGH, or on CP0 when CP1 is LOW, as the this would causean extra count.

Fig.7 Counter expansion.

led matrix display project report

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