How 7 Segment Displays Work: Types, Pinout, and How They Work

Introduction

A 7 segment display is a popular choice for displaying numerical and some alphanumeric characters. The setup consists of 7 LEDs, hence the name. These LEDs are arranged in a specific pattern that resembles the number 8. You can illuminate the display using different combinations to display the digits from 0 to 9 and some letters.

Due to the display’s functionality, you are likely to encounter it in various applications. Examples include digital clocks, calculators, and other devices that need numbers and some letters displayed.

We look at the 7 segment digital display in detail below to understand more about it, how it works, types, pinout diagram, and more.

Structure of a 7 Segment Display

We have already established that the 7 segment displays will have seven LEDs. This is the core of the display to ensure it displays the numbers correctly.

You also get segment labels as part of the structure of the display. Each LED will be assigned a letter. This includes from A to G. The top horizontal segment has A and moves clockwise around the display.

The decimal point or DP is the eighth LED in the display. The job of this LED is to indicate fractional numbers or multiple digits.

The 7 segment display can also be either common anode or common cathode as part of the structure. The common anode means all anodes are connected together. It is the same thing for the common cathode type, where you have all cathodes connected together.

The structure also includes internal wiring. It uses thin wires to connect the different LED segments to the corresponding 7-segment display pin.

Encapsulation is a protective cover of the display. It can be made using plastic or resin. It also helps prevent light bleeding between segments by including light barriers.

Types of 7 Segment Display

The pin configuration of 7 segment display allows it to function correctly. However, there are two main types of display. Below, we look at how they work to understand their applications.

Common Cathode (CC)

This is a common display type where all the cathodes in the circuit are connected to a single pin and then grounded.

For you to illuminate a segment, a positive voltage has to be applied to the corresponding anode. You will find this a common configuration when working with microcontrollers such as Arduino.

Common Anode (CA)

In this type, all the anodes of the LEDs in the circuit are connected together to a single pin and then connected to the positive power supply.

For you to light up a segment in the display, a low voltage is applied to the corresponding cathode. It is not the most common type of configuration compared to the common cathode setup.

How a 7 Segment Display Works

The 7 segment LED display has seven LEDs for displaying the numbers and some letters. They are labelled A to G plus a decimal point.

Each letter or digit needs a specific combination of the segments to be lit so that it can be displayed. Let us say you want to show number 1 on the display, then segments B and C will light. For number 8, all the seven segments have to light up.

A microcontroller or other circuits are commonly used to provide the necessary voltage needed to activate the right segments to display the numbers correctly.

It is also possible to display multiple digits through a technique called multiplexing. This method involves rapidly switching between the different displays, each showing a part of the number. The human eye perceives the digits being shown at the same time due to the persistence of vision.

Applications of 7 Segment Displays

From the 7 segment display pin layout, we can find many uses of the display. Here is what to expect.

• Time display in digital clocks, wristwatches, clock radios, and more
• Basic calculators rely on the use of 7 segment display to show the numbers
• Electronic meters such as energy meters and voltmeters often use this display to show readings
• Speedometers, odometers, and other related automotive displays use the 7 segment display in their applications
• Appliances such as microwaves, ovens, and other countertop appliances will have this display setup to show the cooking time and temperature settings.
• Counters in different setups, such as gyms and others, will have this type of display as well.

It is easy to see how it is possible to come across this type of display in various applications. So long as the numbers and some letters need to be displayed, they can come in quite handy.

Advantages of 7 Segment Displays

• Simplicity makes these displays easily adaptable for use in various operations. The 7-segment display has a straightforward design that makes implementation quite easy.
• They are also cost-effective since they are inexpensive to produce and use. This should make them a budget-friendly solution for displaying numerical data.
• Interfacing with microcontrollers is possible, allowing you to control which numbers are displayed.
• The overall durability of these displays is quite impressive. Being robust means that they can withstand different environmental conditions, thus making them suitable for a wide range of applications.
• The displays are usually easy to read even from a distance. This makes them suitable for various types of applications.
• These displays are known for consuming less power. This is what you want for battery-powered devices.
• You can come across them in various colors, sizes, and configurations. As such, they should be a versatile choice for different projects.

Limitations of 7 Segment Displays

• Even for a large 7 segment display, you are limited to displaying numbers 0 to 9 and a limited set of letters. You cannot use them to display complex characters, symbols, or graphics.
• You may also experience difficulty reading the display at certain angles. From certain angles, you may see the display looking dim or unreadable.
• They are prone to misinterpretation in cases of rotated displays, or when displaying certain letters, you might confuse which one it is.
• Overall customization is limited. You might notice it is not easy to display unique or complex patterns.

How to Interface a 7 Segment Display with a Microcontroller

You need a proper connection of the 7 segment display circuit to the microcontroller for it to work correctly. When you want to connect to the microcontroller, the first thing is to identify the output pin. Choose enough pins to control the segments of the 7-segment display.

Start by connecting each segment A-G and the DP, if necessary, to the output pin of the microcontroller.

Connect the common anode or cathode pin to the appropriate power or ground source. This is usually done through a resistor to ensure you get the right current amount in the circuit.

Next is to write the code that will run the 7 segment display. First, determine the segment patterns. You have to create a set of variables that will map each digit from 0 to 9 and potentially other characters.

Use the microcontroller’s programming language to set the output pins to either LOW or HIGH depending on the display type. This is what helps display the desired character.

You may want to implement a delay between displaying different digits or characters to help make them visible.

7 Segment vs. 14 Segment vs. 16 Segment Display: Know the Differences

You are likely to come across the three in the market, but you are unsure what each can do. So, the 7 segment displays use seven LEDs arranged in a figure eight shape. Such displays will be used for displaying numbers and a few letters. They are commonly used in calculators and digital clocks.

The 14 segment displays offer a wide range of alphanumeric characters. This includes the upper and lowercase letters. Examples include retro-style displays and arcade games.

The 16 segment displays come with an extensive character set compared to the other two options mentioned above. They are capable of displaying a full range of alphanumeric characters and sometimes symbols. They can be found in DVD players, PA displays, and car stereos.

Troubleshooting Common 7 Segment Display Issues

Sometimes the numbers or letters on 7 segment display might not show. For such a case, you need to understand what the issue could be and how to resolve it. Below are some troubleshooting scenarios you are likely to encounter.

Check for broken segments or the display

A visual inspection of the display helps to understand if there is any physical damage. Examples include cracked segments or broken connections.

Testing with a multimeter helps to check for continuity between the segment pins and the common pin. If there is no continuity, then it means there is a broken segment.

An LED test can also be done to test individual segments. Each segment should light up or you may have to replace the segments that do not light up.

Verify the wiring

Perform a schematic check to ensure your wiring matches the one on the schematics. The same goes for the pinout configuration. Sometimes, if you do not connect to the right output pin, you will not get the desired output.

Double-check to ensure the polarity matches the display type. For common cathode displays, apply a positive voltage to the segment pins and the common pin, grounding it to the negative voltage. As for the common anode, ground the segments and apply a positive voltage to the common anode.

Make sure that you are using the appropriate resistors in the circuit. Calculate the resistor values depending on the current and voltage you want to apply to the LEDs.

Check the driving circuit

Ensure that the power supply is providing the circuit with the correct voltage and current for the display to function properly.

Look at the driver ICs. Verify their connections and functionality. You need the right driver IC that is properly configured to work with the display.

If you are experiencing multiplexing issues, ensure that you check the multiplexing logic. This includes the segment and digit selection signals.

Software issues

You may also experience software issues such as incorrect character mapping or timing problems. Always ensure that the software you use correctly maps the input data to the corresponding segments for display.

Conclusion

A 7 segment display works quite well with many applications. We are talking of lifts, ovens, radios, and so much more. Their simplicity and robustness continue to make the display ideal for different environments. That is why you may find them on different machines displaying information. There might be a few limitations like the number of letters it can display, but it is a versatile display on overall. Watch out for a few issues, which are mostly easy to sort out, and keep using the display.