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Seven Segment LED Displays
LED (Light Emitting Diode) is a semiconductor device that emits either visible light or infrared light when it is forward biased. Thus, it is widely used in different electronic devices like TV screens, mobile screens, watches and clocks, remote controls, etc. A light emitting diode (LED) basically converts electrical energy into light energy when an electric current flows through it.
In this article, we will discuss an application of LED in Seven Segment Display. The seven segment displays are extensively used in in different electronic gadgets like calculators, counters, watches, electronic measuring instruments, etc.
What is a Seven Segment LED Display?
Seven Segment Display is an LED based display screen that can display information in the form of decimal numbers. The seven segment display is a used in place of the more complex dot matrix displays. It is called so because it consists of seven segments of light emitting diodes (LEDs) that are assembled like decimal 8 as shown in the following figure.
Seven segments LED display can be used in applications where an electronic display device is required for showing decimal numbers from 0 to 9, sometimes, basic characters as well. Since, it uses LEDs, therefore it is an energy efficient display device. Therefore, it is most widely used in those devices that are powered by a small battery or a cell.
Working of Seven Segment LED Display
A seven segment display consists of seven LED segments arranged like a decimal 8. These LED segments are illuminated to form a pattern that represents a decimal number from 0 to 9. Now, let us understand, how the seven segment LED display work to display different numbers.
When electrical energy is supplied to all the segments, then the seven segment LED display shows the decimal number 8.
When power is given to all the segments and if we disconnect power from the segment ‘g’, then it displays the decimal number 0.
When the power is given to segments "b" and "c" only, then it displays the number 1.
When the power is given to the segments "a", "b", "g", "e", "d", then it displays the number 2.
When the power is given to segments "a", "b", "g", "c", "d", then it displays the number 3.
When the power is given to segments "b", "c", "f", "g", then it displays the number 4.
When the power is given to segments "a", "c", "d", "f", "g", then it displays the number 5.
When the power is given to segments "a", "c", "d", "e", "f", "g", then it displays the number 6.
When the power is given to segments "a", "b", "c", then it displays the number 7.
When the power is given to segments "a", "b", "c", "d", "f", "g", then it displays the number 9.
In this way, we can display any decimal number from 0 to 9 by illuminating a set of LED segments of the seven segment LED display.
Truth Table of Seven Segment LED Display
The following table shows the truth table of a seven segment LED display to display the decimal numbers from 0 to 9.
| Seven Segment Display Output | LED Segments Inputs | ||||||
|---|---|---|---|---|---|---|---|
| a | b | c | d | e | f | g | |
| 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 |
| 1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 |
| 2 | 1 | 1 | 0 | 1 | 1 | 0 | 1 |
| 3 | 1 | 1 | 1 | 1 | 0 | 0 | 1 |
| 4 | 0 | 1 | 1 | 0 | 0 | 1 | 1 |
| 5 | 1 | 0 | 1 | 1 | 0 | 1 | 1 |
| 6 | 1 | 0 | 1 | 1 | 1 | 1 | 1 |
| 7 | 1 | 1 | 1 | 0 | 0 | 0 | 0 |
| 8 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 9 | 1 | 1 | 1 | 1 | 0 | 1 | 1 |
Types of Seven Segment LED Displays
There are two types of seven segment displays available −
Common Cathode Seven Segment Display − In this type of seven segment display, the cathode terminal of all LED segments are connected together to logic 0 (lower voltage level). The logic 1 (higher voltage level) is applied through a current limiting resistor to forward bias the individual LED segments at their anode terminals.
Common Anode Seven Segment Display − In this type of seven segment LED display, the anode terminals of all the LED segments are connected together to the logic 1 (higher voltage level), and the logic 0 (lower voltage level) is used through a current limiting resistor to the individual cathode terminals of LED segments.
Note − Common Anode Seven Segment LED Displays are more popular than Common Cathode Seven Segment Display because logic circuit can sink higher current as compared to they can source.
Applications of Seven Segment LED Displays
Seven Segment LED Displays are widely used in the following devices −
- Digital watches and clocks
- Calculators
- Microwaves
- Remote controls
- Speedometers
- Vehicle odometers
- Clock radios, etc.
Conclusion
Seven segment displays are very commonly used in low power electronic devices like remote controls, watches, clocks, digit measuring instruments, etc. From the above discussion, we may conclude that a seven segment display consists of seven LED (Light Emitting Diode) segments that are illuminated in a pattern to display the numbers from 0 to 9. Seven segment displays are also used to display some basic characters.
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