7 Segment Display: How Does it Work?

The display is one of the popular types of production in embedded displays and devices. All these things have one thing in common, the timer on your kitchen appliances, digital clocks, and bomb timers in movies.

The similarity is that they all use seven-segment displays to show numbers. This article will help you dig deeper into the world of these digital displays and explain everything about them. Keep reading for a consolidated series of all the information you need about the 7-segment production.

What is a 7-Segment Display?

A 7 segment display is one of the oldest forms of the electronic display device for displaying decimal numerals in embedded applications. It is An alternative to the complex dot matrix displays.

These displays have 8 Light-emitting diodes (LEDs) inside for displaying numbers and alphabets.

You can trace the use of these gadgets as far back as 1903 by an individual known as Carl Kinsley. He was the inventor of a method to transmit letters and numbers telegraphically.

seven segments digit display

How Does a 7-Segment Display Work?

A seven-segment display uses Light Emitting Diodes to release light energy in photons. The production emits light to show digits in all seven segments, with the eighth segment being a decimal point.

While the phenomenon happens, bear in mind that an LED is a solid-state optical p-n junction diode. Hence it allows current flow through its junction.

The diode favors current from external voltage to flow forward, and this process is known as electroluminescence. The colors range from red to blue to green depending on the various impurities in the semiconductor materials that help produce it. 

The decimal point comes in handy when connecting two or more seven-segment displays. The reason is to show decimal digits or give a multi-digit presentation.

Preference for LEDs is due to reasons such as:

• their cheapness,
• long life,
• small size,
• availability in various colors,
• easy availability and
• It is easy to integrate them into other electronic components and digital circuits.

However, their main advantage is that you can fit multiple of them in a small compact package forming a seven-segment display. A concept possible thanks to the display's small size.

What are the Different Types of Seven Segment Displays?

You can choose various features for the seven-segment display, including the different types of color and size. However, the most common type is the 14.20mm red 7-segment display since it consumes less current than the other varieties.

It is important to note that the size and color of these gadgets affect the amount of current passing in the circuit.

When it comes to types of this display, two are available. Which are; 

• The Common Anode(CA) 7 Segment Display
• The Common Cathode(CC) 7 Segment Display

What is the Common Anode (CA) 7 Segment Display?

The Common Anode(CA) 7 Segment Display is also commonly known as a CA display. They both have a close resemblance except for the polarity of LEDs and the common terminal.

a typical anode 7-Segment display

The difference is due to the standard pin on the seven-segment display. The plug connects to all the eight anode pins of the LEDs.

In this type of display, all anode connections of the LED segment join to Logic "1". Illuminating individual components occurs by applying a ground logic, also known as "LOW" or Logic "0". This process happens via an emitter follower or a voltage-current collector to the cathode of a particular segment.

Preference is given to the Common Anode displays. CA displays do not sink more current than they source compared to other logic boards.

What is the Common Cathode (CC) 7 Segment Display?

The Common Cathode 7-segment display is also referred to as a standard cathode display (CC display).

As the name suggests, the standard pin connects to the eight cathode pins and the light-emitting diodes. This display is unlike the CA display that connects all the anode pins.

a typical cathode 7-segment display

For the display to work, all cathode connections of the LED segments join to the logic "0" or ground. Individual components illuminate when a "HIGH" or Logic "1" signal applies. The signal applies via an emitter follower to forward bias the respective anode terminals.

You can not replace either of the two types in a circuit since it is similar to connecting the LEDs in reverse. If there is a replacement, there will be no light production.

What is the Seven-Segment Display Pin Configuration?

Below is an image of a common anode 7-segment display that explains how this gadget works. This type has an efficient production and is a standard LED display among logic board enthusiasts.

standard anode 7-segment circuit display showing the number 2

fig. 6 table showing the segment display pin configuration

The above table shows the segment pin configuration from the familiar anode 7-segment circuit display image (fig. 5) above it.

How Does a 7-segment Display Work?

A 7-segment display works by illuminating a particular set of LEDs to display digits or alphabetical characters. For instance, we need to light LED segments corresponding to a, b, g, c, and d to show the numerical digit 3.

Therefore, you can use these segment LEDs to show Arabic numerals from 0 to 9 and characters from A to F.

A truth table such as the one below illustrates the individual segments that need illumination to show numbers and characters.

fig. 7 common anode 7-segment truth table

A typical cathode 7-segment display is the exact opposite of a common anode seven-segment display table.

You can also click this video link to understand further how the seven-segment display works.

How Do We Use a 7-Segment Display?

One of the advantages of this gadget is that it is easy to use and can work without a microcontroller or microprocessor.

The readily available 7-segment counter IC's such as the CMOS 4511 makes it possible. This IC is useful in displays for projects with simple circuits. The IC can also increase or decrease the number on display and drive a one seven-segment display module.

Notwithstanding, using a seven-segment display and an MCU/MPU will connect the eight segment pins to the I/O pins of the microcontroller. The com pin will connect to the ground of the emitter follower depending on the type (CA/CC).

You can then toggle the IO pins in a particular sequence to display specific numbers. As you can see, below is a table showing this specific sequence. The table shows each line for displaying a specific number in the seven-segment display.

For instance, to glow the number "6," we will illuminate all the LEDs except the one in "b" using the bit pattern 10000010. We can similarly display "7" by glowing LEDs associated with a, b, and c. The bit pattern will be 11111000.

fig. 8 sequence for displaying desired numbers

The above format only applies to the common anode type; for a cathode type, replace the  0's with 1's and the 1's with 0's.

What are the Advantages of A 7-Segment Display?

Simple and easy to understand: 7-segment displays are intuitive, presenting numeric data in a clear and straightforward manner. Their segmented design makes it easy for users to quickly read and interpret numbers, making them ideal for a variety of applications such as digital clocks, calculators, and measurement instruments.

Low power consumption (especially for LCDs): 7-segment displays, particularly those using LCD technology, consume minimal power. This efficiency makes them suitable for battery-operated devices and applications where conserving energy is crucial, such as portable instruments and handheld meters.

Widely available and cost-effective: 7-segment displays are mass-produced and readily accessible. Their widespread availability and low production costs make them an economical choice for manufacturers, ensuring affordability in consumer electronics, educational kits, and industrial equipment.

Can display both numeric and some alphabetic characters: While primarily designed for numeric representation, 7-segment displays can also show a limited set of alphabetic characters. This versatility allows them to convey essential information beyond numbers, enhancing their utility in devices like timers and simple message displays.

What are the Disadvantages of A 7-Segment Display?

Limited character set (only numerals and a few letters): The design of 7-segment displays restricts them to displaying digits 0-9 and a few alphabetic characters. This limitation confines their use to applications where detailed text display is not required, reducing their applicability in more complex information displays.

Relatively low resolution compared to other display technologies: 7-segment displays have a low resolution, lacking the pixel density of modern display technologies like LCD or OLED screens. This results in less detailed and less visually appealing characters, making them unsuitable for high-resolution graphical interfaces or detailed text rendering.

Limited customization options for character shapes and styles: The fixed segment layout of 7-segment displays restricts the customization of character shapes and styles. Unlike dot matrix displays or graphic LCDs, they cannot easily support varied fonts or complex graphic designs, limiting their aesthetic and functional flexibility in diverse applications.

Summary

In summary, there are two types of seven-segment displays: Common Anode and Common Cathode. Both have their pros and cons.
Common Anodes are more popular than Common Cathodes because they require less power consumption to display numerical values. However, Common Cathodes offer better contrast ratios.
Both displays are helpful in many everyday applications, including display technology such as digital clocks, numeric keypads, and alphanumeric displays.

You can find circuit boards and other components to understand the seven-segment display further.