seven segment display using 74LS78 IC decoder

BCD TO SEVEN SEGMENT DISPLAY DECODER 1

CHAPTER - 1

INTRODUCTION

1.1 Introduction

In most of our electronic products or projects we need a power supply for converting mains

AC voltage to a regulated DC voltage. For making a power supply designing of each and

every component is essential. Here I’m going to discuss the designing of regulated 5V Power

Supply.

In this project we need fix 5 volt supply for BCD seven segment decoder (IC 74LS47 or IC

74LS48) to control the output and display the output on seven segment display. so first of all

we make 5 volt DC supply by using these component.

List of Component generate fix 5 volt dc supply

1. Step Down Transformer

2. Voltage Regulator IC 7805

3. Capacitors 4. Diodes 5. Registers

6. LED 7. Switch

When we have 5 volt DC supply than we apply as BCD Inputs A, B, C, D on decoder IC

74LS48. We use hear IC 74LS48 because we have cathode seven segment display if we have

anode seven segment display than we use hear IC 74LS48 as a decoder IC. Decoder IC have

4 BCD inputs and seven segment output ( a, b, c, d, e, f, g ).

List of component control display on seven segment display

1. Push Switch

2. Decoder IC 74LS48

3. Register

4. Cathode Seven Segment Display

5. LED


CHAPTER - 2

CIRCUIT DESCRIPTION

2.1 Circuit Connection

The following shows circuit connection of generate 5 volt and decode and display on seven

segment display.

Figure 2.1 Full Circuit diagram of seven segment decoder

2.2 Working Of The Circuit

2.2.1 Step 1 Step - Down Transformer

The most frequently used device in electronic workshops and laboratories is a universal

power supply provides fix DC voltage. As many application we use DC power supply so first

convert AC power supply to DC power supply as a use of DC voltage than we use different

circuit configuration. We required 5 volt supply so we convert AC 230 volt 50 Hz to 5 volt

DC supply. We use at step-down transformer (230 V to 12 Volt and 1 Amp. ) to decrease

voltage and current. These types of step-down transformer decrease 12 volt and 1 Amp.

2.2.2 Step 2 Rectification Process

Rectification process by using diodes (1N4007) . Rectifiers are many types

1. Half wave rectifier


2. Full wave rectifier 3. Bridge rectifier

These rectifiers are rectified the input signal and gave positive side AC wave but for good efficiency we use bridge rectification configuration. In this process any AC signal are remain

then by pass capacitor pass AC signal to input and gave only 12 volt dc supply .

2.2.3 Step 3 Voltage Regulator

Voltage regulator is electronically IC that use for regulate voltage. As a use of circuit voltage regulator are many types but in this circuit configuration we use IC 7805 that regulate output

voltage +5 V.

(a) (b)

Figure 2.2 (a) pins of 7805 voltage regulator (b) Internal circuit configuration of 7805 voltage regulator

2.2.4 Step 4 BCD Inputs Switches

BCD inputs switches are A,B,C,D that are respectively value in decimal are

A = 1 ( 2^0 ) B = 2 ( 2^1 ) C = 4 ( 2^2 )

D = 8 ( 2^3 ) that means when we press A Switch then display 1 and when we press B then display 2 and

etc.

2.2.5 Step 5 BCD To Seven Segment Decoder

Decoder IC are many types but we use in this project is IC 74LS48. This IC particularly use for common cathode seven segment LED display if we use common anode display than the

decoder IC is 74LD47. This decoder IC have four BCD Inputs A,B,C,D and outputs a,b,c,d,e,f,g are seven segment outputs of seven segment display.

As saw seven segment display unit a, b, c, d, e, f, g are LED segment that means if we want to display 1 then b, c are ON state and a, d, e, f, g are OFF state


Figure 2.3 74LS48 decoder configurations with common cathode seven segment display


CHAPTER - 3

COMPONENT DESCRIPTION

3.1 Components Requirements

S. No Components Description

1. Decoder IC 74LS48 Max volt 5.5

Min. volt 4.5

2. Diode 1N4007

3. LED Red Blue

4. Capacitor 1000µF

5. Resistors 220 ῼ

10K ῼ

6. Step –Down Transformer 230V AC - 12 V AC

7. Seven Segment Display Common Cathode Display

8. Switches 4 push switch rating 1 amp

Table 3.1 Components Description


CHAPTER - 4

SEVEN SEGMENTAL DISPLAY

4.1 Introduction

This is basically use for numeric display. It consists of seven segment a, b, c, d, e, f and g . A

segmental display forms the digit to be display by illumination proper segments from the

group. It is use to display 0 to 9 digit and Alphabetic display.

Typically 7-segment displays consist of seven individual colored LED’s (called the

segments), within one single display package. In order to produce the required numbers or

HEX characters from 0 to 9 and A to F respectively, on the display the correct combination of

LED segments need to be illuminated and BCD to 7-segment Display Decoders such as the

IC's 74LS48.

Figure 4.1 Seven Segmental LED Display

A standard 7-segment LED display generally has 8 input connections, one for each LED

segment and one that acts as a common terminal or connection for all the internal display

segments. Some single displays have also have an additional input pin to display a decimal

point in their lower right or left hand corner.

http://www.electronics-tutorials.ws/blog/7-segment-display-tutorial.html


4.2 Types of 7-Segment LED Digital Display.

4.2.1 The Common Cathode Display (CCD) –

In the common cathode display, all the cathode connections of the LED’s are joined

Together to logic “0” or ground. The individual segments are illuminated by

application of a “HIGH”, logic “1” signal to the individual Anode terminals. Use in

this type display to control IC is 74LS48

4.2.2 The Common Anode Display (CAD) –

In the common anode display, all the anode connections of the LED’s are joined

together to logic “1” and the individual segments are illuminated by connecting the

individual Cathode terminals to a “LOW”, logic “0” signal. Use in this type display to

control IC is 74LS47

Figure 4.2 Common Cathode And Common Anode 7-Segment Display

Electrical connection of the individual diodes for a common cathode display and a

common anode display and by illuminating each light emitting diode individually,

they can be made to display a variety of numbers or characters.


4.3 Seven-Segment Display Format

Figure 4.3 7-Segments Display Format

So in order to display the number 3 for example, segments a, b, c, d and g would need to be illuminated. If we wanted to display a different number or letter then a different set of segments would need to be illuminated. Then for a 7-segment display, we can produce a truth table giving the segments that need to be illuminated in order to produce the required

character as shown below.

4.4 Truth Table For A 7-Segment Display

Individual Segments Display

a b c d e F g

1 1 1 1 1 1 0 0

0 1 1 0 0 0 0 1

1 1 0 1 1 0 1 2

1 1 1 1 0 0 1 3

0 1 1 0 0 1 1 4

1 0 1 1 0 1 1 5

1 0 1 1 1 1 1 6

1 1 1 0 0 0 0 7

1 1 1 1 1 1 1 8

1 1 1 1 0 1 1 9

Table 4.1 Truth Table for a 7-segment display

Figure 4.4 Seven-Segments Display Elements for all Numbers.


CHAPTER - 5

BINARY CODED DECIMAL

5.1 Introduction

Binary Coded Decimal (BCD or “8421” BCD) numbers are made up using just 4 data bits or

more , but unlike hexadecimal numbers that range in full from 0 through to F, BCD numbers

only range from 0 to 9, with the binary number patterns of 1010 through to 1111 (A to F) .

Decimal Binary Pattern

BCD 8 4 2 1

0 0 0 0 0 0

1 0 0 0 1 1

2 0 0 1 0 2

3 0 0 1 1 3

4 0 1 0 0 4

5 0 1 0 1 5

6 0 1 1 0 6

7 0 1 1 1 7

8 1 0 0 0 8

9 1 0 0 1 9

Table 5.1 Binary To BCD Convert

5.2 BCD To 7-Segment Decoder Or Driver

The SN54/74LS48 is a BCD to 7-Segment Decoder consisting of NAND gates, input buffers and seven AND-OR-INVERT gates. Seven NAND gates and one driver are connected in pairs to make BCD data and its complement available to the seven decoding AND-OR

INVERT gates. The remaining NAND gate and three input buffers provide lamp test, blanking input/ripple blanking input for the 74LS48.

The circuit accepts 4-bit binary-coded-decimal (BCD) and, depending on the state of the auxiliary inputs, decodes this data to drive other components. The relative positive logic output levels, as well as conditions required at the auxiliary inputs, are shown in the truth

tables. The LS48 circuit incorporates automatic leading and/or trailing edge zero-blanking control

(RBI and RBO). Lamp Test (LT) may be activated any time when the BI/RBO node is HIGH. Both devices contain an overriding blanking input (BI) which can be used to control the lamp intensity by varying the frequency and duty cycle of the BI input signal or to inhibit the

outputs. • Lamp Intensity Modulation Capability (BI/RBO)

• Internal Pull-Ups Eliminate Need for External Resistors • Input Clamp Diodes Eliminate High-Speed Termination Effects


Figure 5.1 IC's SN54/74LS48 And Pin Description

Where A , B , C , D = BCD INPUT RBI = RIPPLE BANKING INPUTS

LT = Lamp-Test Input BI / RBO = Blanking Input or Ripple-Blanking Output

a , b , c , d , e , f , g = OUTPUT


5.3 Logic Diagram Of IC 74LS48

(a)

(b)

Figure 5.2 (A) Logic Diagram Of IC 74LS48, (B) Block Diagram Of IC 74LS48


5.4 Circuit Of BCD To 7 – Segment Display System

Figure 5.3 block diagram of BCD To 7- Segment Display

Figure 5.4 Circuit Diagram Of BCD To 7- Segment Display


CHAPTER - 6

COMPONENTS DESCRIPTION

6.1 TRANSFORMER

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors — the transformer's coils or "windings". Transformer is used here to step down the supply voltage to a level suitable for the low voltage components. The

transformer used here is a 230 / (12V-0-12V) step down transformer.

Figure 6.1 Step-Down Transformer

6.2 RESISTOR

A resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in

accordance with Ohm's law: V = IR. The resistance R is equal to the voltage drop V across the resistor divided by the current I through the resistor. A resistor is a passive two-terminal

electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Practical resistors have a series inductance and a small parallel capacitance; these

specifications can be important in high-frequency applications. In a low-noise amplifier or pre-amp, the noise characteristics of a resistor may be an issue. The unwanted inductance,

excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology. A family of discrete resistors

is also characterized according to its form factor, that is, the size of the device and the position of its leads (or terminals) which is relevant in the practical manufacturing of circuits

using them.


(a) (b)

Figure 6.2 (a) Fix Carbon Resistor (b) Variable Resistor

6.3 LED (Light Emitting Diode) A light-emitting-diode (LED) is a semiconductor diode that emits light when an electric

current is applied in the forward direction of the device, as in the simple LED circuit. The effect is a form of electroluminescence where incoherent and narrow-spectrum light is emitted from the p-n junction.

Figure 6.3 Blue , Red and Green LED

6.4 CAPACITOR

A capacitor (originally known as condenser) is a passive two-terminal electrical component

used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric (insulator), for example,

one common construction consists of metal foils separated by a thin layer of insulating film.


Capacitors are widely used as parts of electrical circuits in many common electrical devices. When there is a potential difference (voltage) across the conductors, a static electric

field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field. An ideal

capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them.

Figure 6.4 Capacitor

Capacitors are widely used in electronic circuits for blocking direct current while allowing

alternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular frequencies, in electric power transmission

systems for stabilizing voltage and power flow, and for many other purposes.

6.5 SEMI – CONDUCTOR DIODE

A diode is a two-terminal electronic component with asymmetric transfer characteristic, with low (ideally zero) resistance to current flow in one direction, and high (ideally infinite)

resistance in the other. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p-n junction connected to two electrical terminals. A vacuum tube diode, now rarely used except in some high-power technologies and by

enthusiasts, is a vacuum tube with two electrodes, a plate (anode) and cathode. The most common function of a diode is to allow an electric current to pass in one direction (called the

diode's forward direction), while blocking current in the opposite direction (the reverse direction). Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to

direct current, including extraction of modulation from radio signals in radio receivers—these diodes are forms of complicated behavior than this simple on conducting electricity until a c


state in which the diode is said to be biased diode varies only a little with the current, and is a function of temperature; this effect can be used as a temperature sensor Semiconductor

diodes' nonlinear current varying the semiconductor materials These are exploited in special purpose diodes that perform many example, diodes are used to

regulate voltage ( voltage surges (avalanche diodes ), to generate radio frequency diodes), and to produce light ( resistance, which makes them useful in some types of circuits. Diodes were the first semiconductor electronic devices abilities was made by German physicist

diodes, called cat's whisker diodes such as galena. Today most diodes are made of germanium are sometimes use

Figure 6.5 Semi-Conductor Diode


CONCLUSIONS

In this project we have developed display BCD and tested 5 volt supply. This can output to a

seven segment display. We used various methods to display decimal number on seven

segment display and various application of display decimal number. A for-generate loop was

also used to create a 4-bit adder / subtracted. Two interchangeable methods were developed

for correcting for invalid BCD numbers. By coupling together two one digit BCD adder

subtracters with a correction factor for negative numbers, a fully functional BCD

adder/subtracter was created. Addition and subtraction of number is also application of seven

segment display


BIBLIOGRAPHY

www.wikipedia.com/LEDdisplay.

www.wikipedia.com/semi-conductordiode.

www.wikipedia.com/capacitor

www.wikipedia.com/resistor.

www.wikipedia.com/sevensegmentdisplay.

www.wikipedia.com/BCDdecoder

www.electonicsproject.com/bcdtosevensegmentdisplay

Motorola ICs 74LS48.pdf

http://www.wikipedia.com/LEDdisplay

http://www.wikipedia.com/semi-conductordiode

http://www.wikipedia.com/capacitor

http://www.wikipedia.com/resistor

http://www.wikipedia.com/sevensegmentdisplay

http://www.wikipedia.com/BCDdecoder

http://www.electonicsproject.com/bcdtosevensegmentdisplay

seven segment display using 74LS78 IC decoder

Engineering

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