Exploring the World of Seven Segment Displays: History, Advantages, Materials, and Implementations

Introduction: A Seven-segment display is an electronic device displaying numerical decimal numbers. It’s an alternative to the more complicated dot matrix displays and is used extensively in digital watches, electronic meters, basic calculators, and other electronic devices that display numerical data.

Advantages of Seven-segment displays: 

The Seven-segment display can display binary information in decimal format. It is a versatile technology used in many applications such as microwave ovens, calculators, washing machines, radios, digital clocks, and other electronic devices.

Materials Used: 

The Seven segments are either made of Light-Emitting Diodes (LEDs) or Liquid Crystal Displays (LCDs). LEDs emit energy in the form of light, while LCDs display liquid crystals and do not directly emit light. The segments can show either one seven-segment or multiple elements in the required order.

History of Seven-Segment Display: 

The Seven-segment display was invented in 1908 by F. W. Wood and was seen in patents. The collection was first made in 1970 using Light-Emitting Diodes (LEDs). Patents for seven-segment displays date back to 1903 when Carl Kinsley invented a method for telegraphically transmitting numbers and letters.

Evolution of Seven-Segment Display: 

The first Seven-segment displays were made with incandescent filaments and an evacuated bulb. Over the years, smaller incandescent light bulbs or LEDs were used instead. In the 1970s, vacuum fluorescent displays were also available. Early LED seven-segment displays had each digit built using a single LED, resulting in tiny digits. Some added magnifying lenses to the design to make the numbers more readable.

Popularity in Different Applications: 

The Seven-segment design is often used in posters and tags where the user can either apply color to preprinted segments or color through a seven-digit template to create figures such as telephone numbers or product prices. Dot-matrix LCDs are now more common than LED displays for many applications, but seven-segment shows are still top-rated, particularly in basic calculators.

Legibility and Calculator Spelling:

 Although typographers have created more legible typefaces, Seven-segment displays remain popular due to their high recognition and visual contrast compared to dot matrix digits. Seven-segment displays, which use a limited range of letters that look like (upside down) numbers, are also used by schoolchildren to form words and phrases using a ” calculator spelling technique.”

Understand the Pin Configuration of Seven-Segment Displays

A seven-segment display is a standard electronic device used to display numerical data, and it typically comes in a 10-pin package. The pin diagram for the seven-segment displays is shown in the image above.

“Eight Pins for LED Display” Eight of the ten pins in the package are LED pins, which can be left as is. The remaining two pins are standard pins located in the center and are internally shorted.

“Common Anode or Common Cathode” Whether the joint pin is an anode or cathode determines whether the display is a common cathode or anode seven-segment display.

“Available from Various Vendors” Seven-segment displays are readily available from various vendors, offering a wide range of options for those needing this versatile technology.

Pin NumberPin NameDescription
1eBased on the type of display connected to ground/Vcc
2dControls the lowest LED in the 7-segment display
3ComBased on the type of display, connected to ground/Vcc
4cControls the decimal-point LED of the 7-segment display
5DPControls the top-right LED of the 7-segment display
6bBased on the type of display connected to ground/Vcc
7AControls the topmost LED in the 7-segment display
8ComBased on the type of display, connected to ground/Vcc
9FControls the top-left LED of the 7 segment display
10gControls the middle LED in the 7-segment display

Understanding its Pinout, Internal Structure, and Implementations

Seven Segment Display is an electronic device that shows information in numerals and characters. The apparatus comprises seven illuminating segments displayed in different combinations to form numbers or symbols.

Top and Bottom View of Seven Segment Display: A Seven Segment Display has seven display segments and one decimal point. The 7 LED segments are identified as A through G and are used to display numbers. An LED package usually consists of all the segments’ cathodes or anodes. A dot or decimal point represents the decimal point of a number.

Internal Structure of Seven Segment Display: 

The internal structure of a Seven Segment Display is complex, using SMD LEDs. The device comprises two parts – the internal circuit and the display. Rectangular-shaped LEDs are used in the internal rotation, enclosed by glass, ceramics, and plastic to protect them.

Implementations of Seven Segment Display: 

The Seven Segment Display has various implementations, including LCDs, LEDs, and electrochromic displays. Other light-generating or controlling techniques include vacuum fluorescent (VFD), cold cathode gas discharge (Panaplex), incandescent filaments, and Numitron. A multiplexed 4-digit display with seven segments and only 12 pins is also possible.

X-Ray of a 7-segment Multiplexed 8-digit LED Display: 

A multiplexed LED display allows one number to be displayed at a time, even though all digits appear light to the naked eye. The flashing of the integer is so rapid that the human eye cannot see it, but older devices may be visible to peripheral vision.

Seven Segment Displays Light Up

Seven Segment Displays Light Up

Have you ever wondered how those bright and colorful displays on calculators, clocks, and other digital devices work? Well, the answer lies in the seven-segment display technology.
A seven-segment display comprises seven LED lights (A-B, C, D, E, F, G) arranged in a figure-eight pattern. By selectively lighting up these LEDs, it’s possible to display any number from 0 to 9. For example, lighting up all seven LEDs will display the number 3, while lighting up only A, B, C, D, and E will display the number 6. To show a number 0, all segments except for G must be lit.

The schematic diagram for a seven-segment display is shown below, with external series resistors included to limit the current levels. The anodes of each LED are connected to a common positive voltage source, +5 V, making it a common-anode arrangement. As shown in the diagram, Grounding point A allows the lighting of individual LED A. This forward biasing of LED A will cause it to light up and produce a bar of light.

New Types of Seven-Segment Displays

There are two main types of seven-segment displays, common cathode, and common anode, each with its unique characteristics and functions.

The Common Anode Seven Segment Display

The Common Anode, Seven Segment Display, operates by applying power externally to the common anode connector, which connects all segments. The ground is connected to the corresponding segment’s connection (a-g) to turn on a segment. The circuit must also include an additional resistor to limit current flow. The truth table provides the necessary information to drive the display and create the desired numerals, starting from 0-9.

Common Cathode Seven Segment Display

In contrast, the Common Cathode Seven Segment Display operates by grounding the common cathode, which connects all the LEDs’ cathodes. The appropriate segment is illuminated by applying power to it. The truth table for this type of display lists the segments that must be powered to display the decimal digits from 0 to 9.

Both common cathode and common anode seven-segment displays have a truth table that can be used to create all decimal digits. These displays have become ubiquitous in digital devices due to their simplicity, reliability, and ease of use. Seven-segment displays are an excellent choice whether you need to display the time, date, or numerical data.

seven-segment Display Truth Table

seven-segment Display Truth Table
seven-segment Display Truth Table

Driving a Seven-Segment Display:

A 7-segment display is a widely used electronic display device to display numerical data. It is made up of seven individual LED segments that are packaged in a single unit. To ensure the proper functioning of the display, each LED segment must be protected from over-current. This is achieved by limiting the forward current and controlling it with an external resistor.

Voltage Requirements:

The LED segments emit light when they are forward-biased, and the light intensity increases linearly with the increasing current. The forward voltage drop of a red LED segment is typically between 2-2.2V, while that of blue and white LEDs is approximately 3.6V. To illuminate the segments correctly, the voltage source must be greater than the forward voltage value.

Current Limiting Resistor:

The current must be limited to prevent LED damage. For a 7-segment red display, each LED segment can draw around 15 mA when illuminated correctly. On a 5V digital logic circuit, the current-limiting resistor value would be calculated as (5V – 2V) / 15mA, approximately 220 ohms.

Driving the Display with Switches:

The switches illuminate the LED segments in a standard anode display. When a button is closed, current flows through the segment reaches the current-limiting resistor and completes the circuit. The segment then lights up. Switches must be closed to light the LED segments and set to ground (LOW). For example, to illuminate the decimal numeral “4”, switches b, c, f, and g need to be closed.

Using a 7-Segment Decoder/Driver:

A 7-segment display is usually driven by a particular type of integrated circuit, also known as a 7-segment decoder/driver. Several types of decoders are available, such as the CMOS 4511 or the TTL 7447. These decoders accept 4-bit binary input and produce seven outputs that can pass current through the appropriate segments and display the decimal number.

Driving a Seven-Segment Display using a 4511:

In a cathode display, each LED segment’s cathode is connected to the ground, and its anode is connected to the 4511 drivers. The output current is limited to a safe level by a 1k ohm resistor. With just four switches or a 4-bit binary signal, the LED display can be controlled and produce up to 16 combinations of decimal digits.

Seven-Segment Display Features

A 7-segment display is a simple and effective way to display numerical data. With some knowledge of LED driving, it is possible to drive the show with switches, a 7-segment decoder/driver, or even a microcontroller. Using a decoder reduces the complexity of the circuit, and it is possible to display numerical data easily. This guide discussed the voltage requirements, the importance of current-limiting resistors, and how to drive a 7-segment display using switches or a 7-segment decoder/driver. We also looked at a specific example of how to navigate the show using a 4511 decoder.

Additional Considerations:

There are a few other essential considerations to keep in mind when working with 7-segment displays:

  1. Segment Persistence: The segments will continue to emit light even after the current is turned off. This phenomenon is known as segment persistence. To avoid this, turning off the draft to each segment as quickly as possible is necessary.
  2. Power Supply: The voltage source must be capable of providing enough current to illuminate all of the segments. If the supply voltage is inadequate, the elements will dim, making the display difficult to read.
  3. Multiplexing: When using multiple 7-segment displays, multiplexing can reduce the number of output lines required. In multiplexing, only one display is illuminated at a time, and the process is repeated rapidly enough to appear as if all displays are illuminated simultaneously.
  4. Display Brightness: The brightness can be adjusted by increasing or decreasing the forward current. This is typically achieved by changing the value of the current-limiting resistor.
  5. Display Size: The size of the 7-segment display can vary, and choosing the right size for your application is essential. The size will affect the collection’s visibility, so selecting a show that is large enough to be easily seen but not so large that it takes up too much space is necessary.

In conclusion

Driving a 7-segment display is a straightforward task that can be accomplished with a bit of knowledge and the right components. Whether you use switches, a decoder, or a microcontroller, this guide should provide the information you need to get started.

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