Displays are widely utilized in embedded systems and devices, with one standout example being the timers on kitchen appliances, digital clocks, and the dramatic bomb timers often seen in movies. What unites them all is the use of seven-segment displays to present numeric information. In this article, we'll delve deeper into the realm of these digital displays, providing a comprehensive overview of their functionality. Continue reading to access a consolidated resource covering all the essential details about seven-segment displays.
What is 7-Segment Display?
The 7-segment display, often referred to as the "seven segment display," is comprised of seven Light Emitting Diodes (LEDs), which is the origin of its name. These LEDs are arranged in a rectangular pattern, as depicted. Each of these seven LEDs is designated as a "segment" because, when illuminated, it contributes to the representation of numerical digits, including both decimal and hexadecimal characters. Interestingly, the history of these devices can be traced back to as early as 1903, credited to an individual named Carl Kinsley. He is recognized as the inventor of a telegraphic method for transmitting letters and numbers. The seven-segment display serves as a simpler alternative to the more intricate dot matrix displays, primarily used for displaying decimal numerals.
These seven-segment displays find extensive application in digital clocks, electronic meters, basic calculators, and various other electronic devices designed for presenting numerical information.
7-Segment Display Pinout
A seven-segment display comprises seven distinct illuminating sections strategically arranged to create numbers and characters through various segment combinations.
These seven segments are instrumental in conveying binary information. Unlike a conventional P-N junction diode, an LED emits light energy rather than heat.
On the other hand, LCDs leverage the properties of liquid crystals to present information without emitting light directly. Both LEDs and LCDs are harnessed for the presentation of desired numbers and letters.
Pinout Configuration
| Pin No. | Pin Name | Description |
| 1 | e | Controls the left bottom LED of the 7-segment display |
| 2 | d | Controls the bottom most LED of the 7-segment display |
| 3 | Com | Connected to Ground/Vcc based on type of display |
| 4 | c | Controls the right bottom LED of the 7-segment display |
| 5 | DP | Controls the decimal point LED of the 7-segment display |
| 6 | b | Controls the top right LED of the 7-segment display |
| 7 | a | Controls the top most LED of the 7-segment display |
| 8 | Com | Connected to Ground/Vcc based on type of display |
| 9 | f | Controls the top left LED of the 7-segment display |
| 10 | g | Controls the middle LED of the 7-segment display |
The Functioning of the 7-Segment Display
A 7-segment display employs Light Emitting Diodes (LEDs) to emit photons and generate illumination, depicting numerical digits across all seven segments, with the eighth segment serving as a decimal point.
During this process, it's crucial to note that an LED functions as a solid-state optical p-n junction diode, permitting the passage of current through its junction.
The diode facilitates the flow of current from an external voltage source, a phenomenon referred to as electroluminescence. The resulting colors vary from red to blue to green, contingent upon the specific impurities within the semiconductor materials involved.
The inclusion of a decimal point proves advantageous when interconnecting two or more 7-segment displays. This arrangement allows for the display of decimal digits or the presentation of multi-digit content.
The choice of LEDs is influenced by factors including:
Cost-effectiveness
Extended lifespan
Compact dimensions
A wide array of color options
Convenient availability
Seamless integration with other electronic components and digital circuits
Nevertheless, their primary advantage lies in the ability to accommodate multiple LEDs within a compact package, enabling the creation of a space-saving seven-segment display – a feat made feasible by the display's diminutive size.
7-Segment Display Types
Two fundamental types of seven-segment LED displays exist:
Common Anode 7 Segment Display
In this variant, all the negative terminals (anodes) of the eight LEDs are linked, while the positive terminals remain separate.
Common Cathode 7 Segment Display
In this configuration, all the positive terminals (cathodes) of the eight LEDs are interconnected, leaving the negative terminals isolated.
Common anode seven-segment displays enjoy greater popularity compared to their cathode counterparts. This preference arises from the fact that logic circuits can handle more current sinking than sourcing, effectively resembling the reverse connection of LEDs.
How Does 7-Segment Display Work?
Seven-segment units typically incorporate Light Emitting Diodes (LEDs), which illuminate when subjected to forward biasing. The brightness of these LEDs is contingent on the magnitude of the forward current.
Therefore, to achieve optimal illumination, the driver supplies the requisite forward current to these LEDs, which is subsequently directed to the seven segments.
7 common anode 7-segment truth table
7-Segment Display Codes
The table provided illustrates the codes for digits 0 through 9 when utilizing a seven-segment LED display in the common anode configuration.
| Number | g f e d c b a | Hex code |
| 0 | 1000000 | C0 |
| 1 | 1111001 | F9 |
| 2 | 0100100 | A4 |
| 3 | 0110000 | B0 |
| 4 | 0011001 | 99 |
| 5 | 0010010 | 92 |
| 6 | 0000010 | 82 |
| 7 | 1111000 | F8 |
| 8 | 0000000 | 80 |
| 9 | 0010000 | 90 |
When transitioning to a common cathode configuration, the coding scheme undergoes alterations.
| Number | g f e d c b a | Hex code |
| 0 | 0111111 | 3F |
| 1 | 0000110 | 06 |
| 2 | 1011011 | 5B |
| 3 | 1001111 | 4F |
| 4 | 1100110 | 66 |
| 5 | 1101101 | 6D |
| 6 | 1111101 | 7D |
| 7 | 0000111 | 07 |
| 8 | 1111111 | 7F |
| 9 | 1001111 | 4F |
For reference, we have included an example of interfacing a 7-segment display with an Arduino UNO below.
How to use a 7-Segment display
One significant advantage of a 7-segment display lies in its user-friendliness. Unlike other display modules, a 7-segment display can function independently, even without the need for a microcontroller or microprocessor.
This autonomy is made possible through the availability of 7-segment counter ICs like the CD4026. When combined with the display, this IC is ideal for projects with uncomplicated circuitry. It can control a single 7-segment display module and manage the displayed number, allowing for incrementing or decrementing.
However, in most cases, a seven-segment display is used in conjunction with a microcontroller (MCU) or microprocessor (MPU). In such scenarios, the eight segment pins are connected to the MCU/MPU's I/O pins, while the common pin is connected to either the ground or Vcc, depending on its type (CC or CA). These I/O pins are then manipulated in a specific sequence to display the desired numbers. The table below illustrates the particular sequence for displaying each number on the seven-segment display. For instance, to display the number "0," all LEDs except the one corresponding to segment "g" should be illuminated, resulting in the bit pattern 11000000. Similarly, to display "1," LEDs associated with segments "b" and "c" should be lit, corresponding to the bit pattern 11111001.
8 sequence for displaying desired numbers
Note: This table applies specifically to Common Anode displays. For Common Cathode displays, you can simply swap the '1's with '0's and the '0's with '1's.
Applications
Deployed in scenarios necessitating larger text size
Not reliant on microcontrollers, making it suitable for petite electronic undertakings
Applied in conjunction with four-segment setups to exhibit four-character measurements or sensor data
Boasts luminous brightness, rendering it fitting for displays in low-light or dim environments
7-Segment Display-based Projects
Electronic die featuring a seven-segment display
Water level gauge
Conclusion
In brief, two variants of seven-segment displays exist: Common Anode and Common Cathode, each with its advantages and drawbacks.
Common Anode displays enjoy greater popularity compared to Common Cathode ones due to their lower power consumption when showcasing numerical data. However, Common Cathode displays excel in providing superior contrast ratios.
Both types find extensive utility in numerous everyday applications, encompassing digital timekeeping devices, numeric input interfaces, and alphanumeric visual displays.
