Understanding the 7 Segment Display for Complete Beginners

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.

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) to display the colon between hours and minutes. A colon consists of 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

Choosing the right 7-segment display involves more than just selecting a color; you must consider the internal electrical configuration and the physical scale of the component. These displays are categorized primarily by how their internal LEDs are wired together, specifically whether they share a positive or negative connection point, and by their physical packaging, which ranges from small single digits to massive industrial units. Understanding these distinctions is vital because a circuit designed for one type will not work with the other without significant modifications to the wiring and the control logic.

In the following subsections, we will break down the differences between common cathode and common anode configurations, as well as the various multi-digit and large-scale variants available to hobbyists.

Common Cathode vs Common Anode 7 Segment Display

Common cathode versus common anode displays were already explained near the beginning of this article. Below is a summary of the differences between the two configurations.

• 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

Controlling a 7-segment display is an exercise in resource management, as you must balance the number of available microcontroller pins against the complexity of your code. While the simplest method involves connecting every segment directly to an output pin, this quickly becomes impractical for multi-digit systems. Engineers have developed several strategies to solve this, ranging from dedicated hardware decoders that handle the “binary-to-visual” translation to software-based multiplexing that tricks the human eye into seeing multiple digits at once. Below, we explore the most common control methods, starting with basic direct connections and moving toward advanced integrated solutions like the TM1637 module.

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

Achieving a clean and professional look with 7-segment displays requires careful attention to current management and wiring organization. Because these displays are often used to convey critical data at a glance, consistency in brightness across all digits is paramount. If you are building a multi-digit display, the physical layout of your resistors and the quality of your power supply will determine whether your project looks like a polished consumer product or a flickering prototype. Additionally, early testing of your display pins is highly recommended, as different manufacturers sometimes vary the internal pinout even for standard-sized parts. Below are further tips that help when working with these displays.

7 Segment Display Tips

• Use individual current-limiting resistors: Always place a resistor (typically 220–470 Ω) on each of the seven segment lines rather than one single resistor on the common pin. A single resistor will cause the display to dim as more segments are lit (e.g., the number “8” will look much dimmer than the number “1”).
• Label segments clearly: Mark your wires or code variables (A–G + DP) to match the standard 7-segment layout. This prevents “scrambled” numbers during the assembly phase.
• Leverage Decoder ICs: For multi-digit projects, using chips like the CD4511 or 74LS47 saves valuable GPIO pins on your microcontroller by converting 4-bit binary data into 7-segment output.
• Implement Multiplexing: To reduce the nest of wires in 4-digit displays, use multiplexing. This technique involves rapidly switching between digits, allowing you to drive all digits using only 7 segment pins plus one “enable” pin per digit.
• Test before soldering: Use a 3V coin cell battery or the diode-test mode on your multimeter to verify which pins correspond to which segments before you commit to a PCB or breadboard layout.
• Account for Forward Voltage: Remember that different colors (Red, Green, Blue) have different forward voltage drops. Ensure your resistor values are calculated specifically for the color of your display to prevent burnout or uneven lighting.
• Use a Logic Level Shifter: If you are driving a 5V display with a 3.3V microcontroller (like an ESP32 or Raspberry Pi), ensure your logic high is sufficient to trigger the segments or use a shifter to prevent flickering.

Did You Know About 7 Segment Displays?

The 7-segment display is a masterpiece of minimalist design, relying on the concept of “glyph simplification” to represent the entire decimal system with the fewest possible moving (or lighting) parts. While we take them for granted in our kitchen appliances and gas station signs, their development was a major milestone in the transition from mechanical “nixie tubes” to the solid-state digital world we live in today. These displays are not just about numbers; they represent a specific era of industrial design where legibility and power efficiency were the primary engineering constraints. Below are some more interesting facts about these displays.

Interesting 7 Segment Display Facts

• The Century-Old Patent: While they feel modern, the first patent for a 7-segment arrangement was actually granted in 1908 to F. W. Wood, who used it for power plant signal systems.
• Persistence of Vision: In almost every digital clock you see, only one digit is actually “on” at any given microsecond. They flicker so fast that your brain perceives them as being constantly illuminated.
• Slanted for Speed: Most 7-segment displays are slanted at a 10° or 12° angle. This is called an “italic” slant, and it is designed to help the human eye recognize the shape of the numbers more quickly from a distance.
• Hexadecimal Capability: While primarily for decimals, 7-segment displays are commonly used in computer engineering to show Hexadecimal (0–9 and A–F), though characters like ‘B’ and ‘D’ must be shown in lowercase (‘b’ and ‘d’) to avoid confusion with ‘8’ and ‘0’.
• Nixie Tube Successors: Before LEDs, “Nixie tubes” were used to show numbers. 7-segment LEDs killed the Nixie tube market in the 1970s because they were cheaper, more durable, and required much lower voltages to operate.
• Space-Saving Design: Some ultra-miniature 7-segment displays are smaller than a grain of rice, used in high-end optical equipment and military head-up displays.

Frequently Asked Questions About 7 Segment Displays

Integrating a display into a circuit often leads to unexpected behavior, such as segments that stay partially lit or digits that show incorrect symbols. This FAQ addresses the most common technical hurdles beginners face, from electrical ghosting to software-based digit control. Understanding these nuances will help you move beyond basic “Hello World” tutorials and into building robust, reliable electronics.

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.

What is the difference between a 7 segment and 8 segment display?

In practical terms, they are usually the same thing. A “7-segment” display refers to the seven bars used to form numbers. However, almost all physical modules include an 8th LED for the decimal point (DP). Some specialized “14-segment” or “16-segment” displays exist, which use diagonal bars to allow for a full range of alphanumeric characters (A–Z).

Why do some segments look “ghostly” or stay dimly lit when they should be off?

This is a common issue in multiplexed displays called “ghosting.” it happens when the microcontroller switches the “digit pin” before the “segment pins” have fully updated. To fix this, you should briefly turn off all segments (a “blanking” interval) for a few microseconds before switching to the next digit in your code.

How do I calculate the correct resistor for my display?

You can use the formula​ $R = \frac{V_{supply} – V_{forward}}{I_{desired}}$. For a standard red LED segment on a 5V Arduino, the forward voltage (Vf​) is usually about 2.0V. If you want a current (I) of 10mA (0.01A), the math is: $\frac{5 – 2}{0.01} = 300Ω$.

Can I drive a large 7-segment display directly from an Arduino?

Usually, no. Large displays (over 1 inch) often have multiple LEDs wired in series for each segment, requiring 12V or even 24V to light up. Since an Arduino pin can only provide 5V and limited current, you will need to use a transistor (like a PN2222) or a ULN2003 driver chip to switch the higher voltage required by the large display.

What is the advantage of using a TM1637 or MAX7219 module?

These modules contain a “display driver” chip that handles all the multiplexing and current limiting for you. Instead of using 12 pins and writing complex timing code, you only use 2 or 3 pins and send simple commands like display.showNumber(1234). This frees up your microcontroller’s processor to handle other tasks like reading sensors or keeping time.

How do I identify the “Common” pin if the datasheet is missing?

Set your multimeter to the “diode” or “continuity” setting. Put one probe on a middle pin and tap the other probe on any corner pin. If a segment lights up, the pin your first probe is touching is the “Common” pin. If you have to swap the red and black probes to get it to light, that tells you whether it is Common Anode (positive) or Common Cathode (negative).

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.