A 7 segment display is an electronic display device used to display decimal numerals and a limited set of characters. It is widely used in digital clocks, calculators, basic measuring instruments, and embedded systems. Each digit consists of 7 individual LED segments arranged in a figure-8 pattern, which can be lit in different combinations to represent numbers and some letters.
Table of Contents
- What Beginners Need to Know About 7 Segment Displays
- What Is a 7 Segment Display and How Does It Work?
- Types of 7 Segment Displays
- How to Control a 7 Segment Display
- Tips for 7 Segment Display Use
- Did You Know About 7 Segment Displays?
- Frequently Asked Questions About 7 Segment Displays
- Conclusion
What Beginners Need to Know About 7 Segment Displays
Seven segment displays usually join all the cathodes or all the anodes of the LEDs in the display together. When all the cathodes are joined, the display is called a common cathode seven segment display. When all the anodes are joined, they are called common anode seven segment displays.
Types of 7 Segment Displays:
- Common Cathode 7 Segment Display: All the cathodes (negative terminals) of the LEDs are connected together.
- Common Anode 7 Segment Display: All the anodes (positive terminals) are connected together.
The following images show how the LEDs of a common cathode and common anode seven segment display are wired. This is just an example. Always check the datasheet for the specific display that you are using in order to find the correct pin numbering and wiring of your particular device. Various 7 segment display datasheets can be found from manufacturers, for example SunLED.
As can be seen in the above images, the 7 segments or LEDs of the display are labelled from a through to g. An additional LED is used for the decimal point and is labelled DP.
Digit Variants:
- Single Digit 7 Segment Display can be used to display 0 to 9 and some letters on its own
- 4 Digit 7 Segment Display, or a combination of any number of 7 segment displays to make up the desired number of digits
- Large 7 Segment Display for improved visibility at a distance
Control Methods:
- Direct GPIO Control using microcontrollers, for example using an Arduino board
- Via 7 Segment Decoder ICs like 74LS47 or CD4511
Now let’s explore everything you need to know about using and understanding a 7 segment digital display.
What Is a 7 Segment Display and How Does It Work?
A 7 segment display is a simple and efficient way to display numbers using 7 LEDs arranged in the shape of the number “8”. By selectively lighting up segments labeled A through G, numbers from 0 to 9 and some alphabetic characters can be shown. An optional eighth segment, the decimal point, is included in many versions.
These displays are typically used in devices where only numeric output is required, such as timers, counters, and basic meters. They are commonly referred to as 7 segment LED displays or seven segment digital displays.
How to Show Numbers on a Seven Segment Display
The following image shows which LED segments to light up in order to display numbers from 0 to 9.
As can be seen in the above image, segments a, b, c, d, e and f are lit up to display the number 0. To display the number 1, only segment b and c are lit up. Segments a, b, g, e and d form the number 2, and so forth for each number. All 7 segments are lit up to display the number 8.
Limited Set of Characters on a Seven Segment Display
A limited set of alphabet characters can be displayed on a seven segment display. The following image shows the characters: A, b, C, d, E, F, H, I, J, L, n, o, P, r, S, U, y and Z
How to Show Time on a Seven Segment Display
The following image shows how a combination of four 7 segment displays are used to make a digital time display. The third display from the left is inverted (put in upside-down) in order to display the colon between hours and minutes, using the decimal point from the second digit and from the third digit.
Although a four digit display can be made up of four separate 7 segment displays, four digit 7 segment LED displays are also available. In fact dual digit, three digit and four digit displays are common. Each of these types of displays are molded into a single unit. For example a four digit display is a single molded unit that contains four seven segment digits.
Types of 7 Segment Displays
Common Cathode vs Common Anode 7 Segment Display
- Common Cathode: All cathodes are tied together. The common cathode is connected to GND or 0V (zero volts) of the power supply. To illuminate a segment, apply a HIGH signal to the segment pin, using an appropriate current limiting resistor.
- Common Anode: All anodes are tied together. The common anode is connected to the positive supply rail. To light up a segment, apply a LOW signal to the segment pin, using an appropriate current limiting resistor.
Understanding the wiring of each type is critical when designing circuits. The image below shows an example of a single digit seven segment display from SunLED. This is from the XDxx14x Series and has the part number XDMDK14A. Refer to the XDMDK14A datasheet if using this part.
The image below shows the schematic symbol for the part, the pin numbering on the physical device, and the internal wiring of the LEDs in the device.
4 Digit 7 Segment Display
A 4 digit 7 segment display includes four digit sections in a single package, often with multiplexed control. This type is widely used in clocks and counters. It can also be made out of four single seven segment displays stacked together.
Examples of 4 digit seven segment displays are the XDUR06A4 from SunLED, which has a 0.25 inch digit height, and the XDUR14A4 from SunLED, which has a 0.56 inch digit height.
Large 7 Segment Display
A large 7 segment display is designed for readability from a distance, ideal for industrial timers or outdoor counters.
How to Control a 7 Segment Display
Direct Connection to Microcontroller
Each segment is connected to a microcontroller pin. This is practical for simple applications or single-digit displays. The following image shows a 7 segment display connected directly to microcontroller pins PA0 to PA7 through current limiting resistors. The circuit shows a 3.3V supply on the anode pins of a common anode display. This supply voltage could also be 5V if driving the display from a 5V Arduino.
Using a 7 Segment Decoder
A 7 segment decoder like the 74LS47 or CD4511 chips takes a binary input and drives the correct segments automatically. This reduces the number of required microcontroller pins.
An example of a CD4511 is the CD4511B from Texas Instruments.
An example of a 74LS47 chip is the SN74LS47 from Texas Instruments.
Controlling with Arduino
You can easily control a 7 segment display with Arduino. For multi-digit displays, libraries like SevSeg or TM1637 simplify code and control. An example project from the Arduino project hub that drives a single 7 segment display from an Arduino Uno is the One Digit 7-Segment LED Display project.
Example Use: 4 Digit 7 Segment Arduino Clock
With libraries and multiplexing, you can build a digital clock using a 4 digit 7 segment Arduino setup.
Transistor Multiplexer Circuit for Two Seven Segment Displays
The following circuit shows how to drive two seven segment displays using transistors. Pins that start with PA are microcontroller pins in the circuit. Of course the segments of the display can be driven by an IC like the SN74HC595 instead of individual transistors so that fewer pins are needed.
You can open a bigger image of the circuit for easier viewing.
How the Transistor Multiplexer Circuit Works
In this circuit, the idea is to drive both displays with only 8 microcontroller pins for the segments, and two microcontroller pins for control. This is called multiplexing. It works by switching the first display on using microcontroller pin PA11 that drives transistors Q10 and Q9. With power switched on the anode pins of the first display, the desired segments are switched on using microcontroller pins PA0 to PA7, to display the desired number or digit. The desired digit is displayed for a certain time, and then power to the display is switched off.
After this, power to the second display is switched on to its anode pins, and the desired digit displayed using microcontroller pins PA0 to PA7 again. The LEDs are left on for a certain amount of time, and then the first display is switched back on with its desired digit to display again.
Because power is switched back and forth between the two displays very fast, they both appear to be on at the same time. The eye perceives both displays showing their desired digits. In this way, only 8 pins are used to operate both displays instead of 8 pins per display. With the control pins included in the count, 10 pins are used instead of 16 pins of the microcontroller.
Controlling a 4 Digit 7 Segment Display with TM1637 Module
One of the most convenient ways to work with a 4 digit 7 segment display is by using a module like the LED 4×7 Segment Display Module TM1637. This display is often referred to as a 4-digit LED Tube Display. It integrates seamlessly with microcontrollers such as the Arduino, making it ideal for beginners and hobbyists.
The TM1637 module simplifies wiring and control by using just two data lines (DIO and CLK) to communicate with the microcontroller via a serial interface. This significantly reduces the number of GPIO pins required compared to manually controlling each segment.
Example Key Features of a TM1637 7 Segment Display Module:
- Display Type: 4-digit, 7 segment LED display
- Digit Size: 0.56 inch
- Driver Chip: Integrated TM1637
- Interface: 2-wire serial (CLK and DIO)
- Common Type: Common cathode 7 segment display
- Use Cases: Time display, temperature, counters, and more
- Display Size: 50mm × 19mm
Each digit can be controlled individually, or the entire display can act as a single unit for displaying multi-digit numbers. Multiple modules can be daisy-chained to form larger 7 segment digital displays for more complex outputs. With the TM1637, there’s no need to handle a separate 7 segment decoder or deal with complex multiplexing logic, since everything is handled on the module itself.
This makes the TM1637-based 7 segment LED display one of the easiest ways to implement numeric displays in embedded projects, especially when combined with libraries readily available for platforms like Arduino.
Tips for 7 Segment Display Use
- Use current-limiting resistors (typically 220–330 Ω) on each segment.
- Label segments (A–G + DP) clearly when wiring to avoid confusion.
- Prefer decoder ICs for displays with multiple digits to save GPIO pins.
- Multiplexing can reduce wiring complexity for multi-digit displays.
- Test segments individually before integrating into larger circuits.
Did You Know About 7 Segment Displays?
- The first use of a seven segment display dates back to 1908 in a patent by F. W. Wood.
- Eight segment displays are rarely used but may include additional segments for specific characters.
- LCD versions exist, but the seven segment LED display remains dominant in embedded systems.
- Large public counters and scoreboards often use large 7 segment displays for visibility.
Frequently Asked Questions About 7 Segment Displays
What is the difference between a 7 segment and 8 segment display?
A 7 segment display has seven segments for numeric display. An 8 segment display adds an extra segment to allow more complex characters.
Can I connect a 7 segment display directly to Arduino?
Yes, you can connect a 7 segment display to Arduino directly for simple setups, but use resistors and watch pin limits. For multiple digits, use a library or shift registers.
What does a 7 segment decoder do?
A 7 segment decoder converts binary-coded decimal (BCD) inputs into control signals for the 7 segments, making it easier to drive displays.
How do I know if I have a common anode or cathode display?
Use a multimeter in diode test mode. If the segments light up when the negative lead is on the common pin, it’s a common cathode display. If they light up when the positive lead is on the common pin, it’s a common anode display.
What are 4 digit 7 segment displays used for?
They are used in digital clocks, timers, counters, and scoreboards where multiple digits are required.
Conclusion
A 7 segment display is a simple yet powerful component in electronics, perfect for displaying numeric data in embedded systems. Whether you’re building a digital clock, a counter, or a simple user interface, understanding how seven segment displays work and how to control them is essential for any electronics enthusiast.