7 seg part 2

Seven segment display

Introduction

As a part of curriculum of our college for the second year, we were given the choices to select a project in electronics workshop. We chose seven segment led display as our ELWS project.

We chose seven segment led display as our project since it contained an IC, A seven segment display unit and a switch, which made it interesting for us.

KNOWLEDGE RECEIVED FROM THIS PROJECT

How to use the 4511 7-segment decoder/display driver IC Gain familiarity with the BCD code How to use 7-segment LED assemblies to create decimal digit

displays How to identify and use both "active-low" and "active-high" logic

inputs

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Block Diagram

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CIRCUIT DIAGRAM

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COMPONENT LIST

4511 BCD-to-7seg latch/decoder/driver Common-cathode 7-segment LED display Eight/Four-position DIP switch Four 10 kΩ resistors Seven 470 Ω resistors One 6 volt battery

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CIRCUIT DESCRIPTION

Seven-Segment Display Layout

The illustration above shows the basic layout of the segments in a seven-segment display. The segments themselves are identified with lower-case letters "a" through "g," with segment "a" at the top and then counting clockwise. Segment "g" is the center bar.

Most seven-segment digits also include a decimal point ("dp"), and some also include an extra triangle to turn the decimal point into a comma. This improves readability of large numbers on a calculator, for example. The decimal point is shown here on the right, but some display units put it on the left, or have a decimal point on each side.

In addition, most displays are actually slanted a bit, making them look as if they were in italics. This arrangement allows us to turn one digit upside down and place it next to another, so that the two decimal points look like a colon between the two digits. The technique is commonly used in LED clock displays.

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Seven-segment displays can be packaged in a number of ways. Three typical packages are shown above. On the left we see three small digits in a single 12-pin DIP package. The individual digits are very small, so a clear plastic bubble is molded over each digit to act as a magnifying lens. The sides of the end bubbles are flattened so that additional packages of this type can be placed end-to-end to create a display of as many digits as may be needed.

The second package is essentially a 14-pin DIP designed to be installed vertically. Note that for this particular device, the decimal point is on the left. This is not true of all seven-segment displays in this type of package.

One limitation of the DIP package is that it cannot support larger digits. To get larger displays for easy reading at a distance, it is necessary to change the package size and shape. The package on the right above is larger than the other two, and thus can display a digit that is significantly larger than will fit on a standard DIP footprint. Even larger displays are also available; some digital clocks sport digits that are two to five inches tall.

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Seven-segment displays can be constructed using any of a number of different technologies. The three most common methods are fluorescent displays (used in many line-powered devices such as microwave ovens and

some clocks and clock radios), liquid crystal displays (used in many battery-powered devices such as watches and many digital instruments), and LEDs (used in either line-powered or battery-powered devices). However, fluorescent displays require a fairly high driving voltage to operate, and liquid crystal displays require special treatment that we are not yet ready to discuss. Therefore, we will work with a seven-segment LED display in this experiment.

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4511 BCD to 7-segment latch/decoder/driver

PINNING:

DA to DD address (data) inputsEL latch enable input (active LOW)BI ripple blanking input (active LOW)LT lamp test input (active LOW)Oa to Og segment outputs

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Schematic diagram of output stage

The 4511 is a BCD to 7-segment decoder driver. Its function is to convert the logic states at the outputs of a BCD, or binary coded decimal, counter like the 4510 into signals which will drive a 7-segment display. The display shows the decimal numbers 0-9 and is easily understood.

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WORKING

This experiment is more of an introduction to the 4511 decoder/display driver IC than it is a lesson in how to "build up" a digital function from lower-level components. Since 7-segment displays are very common components of digital devices, it is good to be familiar with the "driving" circuits behind them, and the 4511 is a good example of a typical driver IC.

Its operating principle is to input a four-bit BCD (Binary-Coded Decimal) value, and energize the proper output lines to form the corresponding decimal digit on the 7-segment 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 dropping resistor, we must use seven 470 Ω resistors placed in series between the 4511's output terminals and the corresponding terminals of the display unit.

Most 7-segment displays 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 4511 display driver IC requires a

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common-cathode 7-segment display unit, 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 display. 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"). What happens for the binary numbers 1010 (10) through 1111 (15)? Read the datasheet on the 4511 IC and see what the manufacturer specifies for operation above an input value of 9. In the BCD code, there is no real meaning for 1010, 1011, 1100, 1101, 1110, or 1111. These are binary values beyond the range of a single decimal digit, and so have no function in a BCD system. The 4511 IC is built to recognize this, and output (or not output!) accordingly.

Three inputs on the 4511 chip have been permanently connected to either Vdd or ground: the "Lamp Test," "Blanking Input," and "Latch Enable." To learn what these inputs do, remove the short jumpers connecting them to either power supply rail (one at a time!), and replace the short jumper with a longer one that can reach the other power supply rail. For example, remove the short jumper connecting the "Latch Enable" input (pin #5) to ground, and replace it with a long jumper wire that can reach all the way to the Vdd power supply rail. Experiment with making this input "high" and "low," observing the results on the 7-segment display as you alter the BCD code with the four input switches. After you've learned what the input's function is, connect it to the power supply rail enabling normal operation, and proceed to experiment with the next input (either "Lamp Test" or "Blanking Input").

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When the 4511 is set up correctly, the outputs follow this 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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There is a question about whether the 6's and 9's should have tails. The 4511 produces a display without tails. If other binary values, greater than 1 0 0 1, are connected to the inputs of the 4511, the outputs are all 0's and the display is blank.

Advantages & Disadvantages of 7 Segment LED Display

Seven-segment displays are cheap and reliable.

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. Seven-segment LED displays, like all technology, have advantages and disadvantages.

Cost1. Light 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 will reveal packages of hundreds of LEDs for only a few dollars.

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Simplicity2. Seven-segment displays are extremely simple electronic circuits. A

simple seven-segment display 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).

Reliability3. Since 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 environments from 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.

Efficiency4. LED 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.

Limitations5. Most seven-segment displays are limited to displaying the 16

hexadecimal characters. Some can display only the numbers 0

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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 a limited number of combinations for the seven segments on the display.

Production6. Because LEDs are so cheap to produce and so easy to make, many

manufacturers have sprung up over the past several decades. There is very little regulation in terms of making LEDs, excluding the environmental regulations regarding pollution, and it is therefore easy to find a manufacturer that produces substandard LEDs. The only way to know for sure if a manufacturer produces quality LEDs is by recommendation or buying and testing the product yourself.

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Conclusion

By using 4511 decoder IC we can show decimal output of BCD inputs.

Where input is given by dip switch on output is observed on 7-segment LED display unit.

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BIBLIOGRAPHY

1. WIKIPEDIA

2. ELECTRONICS FOR YOU (MAGAZINE)

3. DATASHEET OF 4511 DECODER

4. BUILDINGGADGET.COM

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Documents

7 seg part 2