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Assignment

On

Seven Segment Display

Submitted to:- Submitted by:-

Ms. Gagandeep Kaur Saurabh Prabhakar

Roll no. 100905067

B.Tech 3rd year

EIC 4

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Introduction

Seven-segment displays are very common and have been for quite some time. They can be found

everywhere from the price signs at gas stations to the display on your microwave oven to digital

wristwatches. LED seven-segment displays have become very popular in consumer electronics,

mainly because of their low power usage, ease of production and cost effectiveness

A seven segment display is the most basic electronic display device that can display digits from

0-9.. The most common configuration has an array of eight LEDs arranged in a special pattern

to display these digits. They are laid out as a squared-off figure 8. Every LED is assigned a

name from 'a' to 'h' and is identified by its name. Seven LEDs 'a' to 'g' are used to display the

numerals while eighth LED 'h' is used to display the dot/decimal.

Concept and visual structure

A seven segment display, as its name indicates, is composed of seven elements. Individually on

or off, they can be combined to produce simplified representations of the Arabic numerals. Often

the seven segments are arranged in anoblique(slanted) arrangement, which aids readability.

Each of the numbers 0, 6, 7 and 9 may be represented by two or more different glyphs on seven-

segment displays.

The seven segments are arranged as a rectangle of two vertical segments on each side with one

horizontal segment on the top, middle, and bottom. Additionally, the seventh segment bisects the

rectangle horizontally. There are also fourteen-segment displays and sixteen-segment

displays (for full alphanumeric; however, these have mostly been d by dot-matrix displays.

The segments of a 7-segment display are referred to by the letters A to G, as shown to the right,

where the optional DP decimal point(an "eighth segment") is used for the display of non-integer

numbers.

http://en.wikipedia.org/wiki/Oblique_typehttp://en.wikipedia.org/wiki/Oblique_typehttp://en.wikipedia.org/wiki/Oblique_typehttp://en.wikipedia.org/wiki/0_(number)http://en.wikipedia.org/wiki/6_(number)http://en.wikipedia.org/wiki/7_(number)http://en.wikipedia.org/wiki/9_(number)http://en.wikipedia.org/wiki/Rectanglehttp://en.wikipedia.org/wiki/Fourteen-segment_displayhttp://en.wikipedia.org/wiki/Sixteen-segment_displayhttp://en.wikipedia.org/wiki/Sixteen-segment_displayhttp://en.wikipedia.org/wiki/Dot-matrixhttp://en.wikipedia.org/wiki/Decimal_pointhttp://en.wikipedia.org/wiki/File:7-segments_Indicator.gifhttp://en.wikipedia.org/wiki/Decimal_pointhttp://en.wikipedia.org/wiki/Dot-matrixhttp://en.wikipedia.org/wiki/Sixteen-segment_displayhttp://en.wikipedia.org/wiki/Sixteen-segment_displayhttp://en.wikipedia.org/wiki/Fourteen-segment_displayhttp://en.wikipedia.org/wiki/Rectanglehttp://en.wikipedia.org/wiki/9_(number)http://en.wikipedia.org/wiki/7_(number)http://en.wikipedia.org/wiki/6_(number)http://en.wikipedia.org/wiki/0_(number)http://en.wikipedia.org/wiki/Oblique_type

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7 segment display Circuit Diagram

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Circuit Diagram of BCD to Seven segment decoder.

WorkingIts operating principle is to input a four-bit BCD (Binary-Coded Decimal) value, and energizethe proper output lines to form the corresponding decimal digit on the 7segmen LED display.

The BCD inputs are designated A, B, C, and D in order from least-significant to most-

significant. Outputs are labeled a, b, c, d, e, f, and g, each letter corresponding to a standardized

segment designation for 7 segment displays. Of course, since each LED segment requires its own

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dropping resistor, we must use seven 470 resistors placed in series between the 4511's output

terminals and the corresponding terminals of the display unit.

Most 7 segmentdisplays also provide for a decimal point (sometimes two!), a separate LED and

terminal designated for its operation. All LEDs inside the display unit are made common to each

other on one side, either cathode or anode. The 4511display driver IC requires a common-cathode 7 segmentunit, and so that is what is used here.

After building the circuit and applying power, operate the four switches in a binary counting

sequence (0000 to 1111), noting the 7 segment. A 0000 input should result in a decimal

"0"display, a 0001 input should result in a decimal "1"display, and so on through 1001 (decimal

"9").

Truth table

BCD inputs segment outputsdisplay

D C B A a b c D e f g

0 0 0 0 1 1 1 1 1 1 0

0 0 0 1 0 1 1 0 0 0 0

0 0 1 0 1 1 0 1 1 0 1

0 0 1 1 1 1 1 1 0 0 1

0 1 0 0 0 1 1 0 0 1 1

0 1 0 1 1 0 1 1 0 1 1

0 1 1 0 0 0 1 1 1 1 1

0 1 1 1 1 1 1 0 0 0 0

1 0 0 0 1 1 1 1 1 1 1

1 0 0 1 1 1 1 0 0 1 1

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Two types of LED 7-segment displays: `

Common cathode (CC) Common anode (CA).

The difference between the two displays is the common cathode has all the cathodes of the 7-segments connected directly together and the common anode has all the anodes of the 7-segments connected together.

When working with a CA seven segment display, power must be applied externally to the theanode connection that is common to all the segments. Then by applying a ground to a particular

segment connection (a-g), the appropriate segment will light up. An additional resistor must be

added to the circuit to limit the amount of current flowing thru each LED segment.

For the use of this seven segment the common cathode connection must be grounded and powermust be applied to appropriate segment in order to illuminate that segment.

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IC 7447

The IC7447 is a BCD to 7-segment pattern converter.

The IC7447 takes the Binary Coded Decimal (BCD) as the input and outputs the relevant 7

segment code.

We connect first four pins of the microcontroller Port 2 to the 7447 and the Output 8 pins of7447 to the 8 legs of the LED as shown in the figure. Te circuit diagrams are shown below, the

first figure is interfacing the CA LED where as the second is of CC LED.

The number required to display is sent as the lower nibble of the Port 2 of the Microcontroller.The 7447 converts the four input bits (BCD) to their corresponding 7-segment codes. The

outputs of the 7447 are connected to the 7-segment display.

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Advantages of seven segment display:-

CostLight emitting diodes (LEDs) are extremely cheap. Diodes are one of the most simple electrical

components , and they are extremely easy to make. A trip to your local electronics store willreveal packages of hundreds of LEDs for only a few dollars.

SimplicitySeven-segment displays are extremely simple electronic circuits. A simple seven-segmentdisplay circuit consists of four input leads; a BCD chip, which contains logic gates to translate

the four leads into seven binary signals, or integrated circuit chip; and the seven-segment display

itself. Most seven-segment displays are capable of displaying all 16 hexadecimal values (1

through 9 and A through F).

ReliabilitySince the seven-segment circuit is so simple, there is a decreased risk of circuit malfunction due

to component failure. Seven-segment LED displays are used in a wide range of environmentsfrom very hot to well below freezing. As there is no liquid inside the unit to freeze, as there is in

LCD displays, an LED display can operate at very low temperatures.

EfficiencyLED displays in general are extremely efficient. Diodes dissipate very little energy. Light-emitting diodes emit slightly more energy than a standard diode in order to produce the photons

(light) that you see, but the voltage drop across a typical LED is so small that it is negligible.

Because of this high efficiency, many electronics makers favor LED technology over LCD

technology because it lowers power supply requirements and reduces the cost of using devices.

Limitations

Most seven-segment displays are limited to displaying the 16 hexadecimal characters. Some can

display only the numbers 0 through 9. Although LED technology exists to display more than

this, seven-segment displays are limited to possible binary combinations of the four input leads,

for a total of 16. Integrated circuit technology can increase this somewhat, but there are still alimited number of combinations for the seven segments on the display.

Applications

Instrument led display In calculator as a display In digital watches IR LED finds application in burglar alarm system.

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Refrences

Electrical and electronic measurements by A K SAHNEY Digital electronics by MORRIS MANO WIKIPEDIA Digital Electronics by ANAND KUMAR