In this tutorial, we will have a basic introduction to 7 Segment Display. They are commonly used to display digits from 0 to 9 and also few alphabets (usually, A to F).
What is 7 Segment Display?
It is the most common device used for displaying digits and alphabet. You can see the 7 Segment Display devices in TV shows counting down to ‘0’. Use of LEDs in displays made it more popular.
The binary information can be displayed in the form of decimal using this display. Its wide range of applications is in microwave ovens, calculators, washing machines, radios, digital clocks etc.
The displays are made up of either LEDs (Light Emitting Diode) or LCDs (Liquid crystal display). LED is P-N junction diode which emits the energy in the form of light, differing from normal P-N junction diode which emits in the form of heat.
Liquid crystal displays (LCD) use the properties of liquid crystal for displaying. LCD will not emit the light directly. These LED’s or LCD are used to display the required numeral or alphabet. Single 7 segment or number of segments arranged in an order meets our requirements.
Pin Configuration of 7 Segment Display
Generally, these types of displays are available in 10 pin package. The pin diagram of this display is shown in the above figure. It is an electronic circuit consisting of 10 pins.
Out of 10 pins, 8 are LED pins and other 2 pins in middle are common pins and these are internally shorted. Depending on either the common pin is the cathode or anode, it can be either named as a common cathode or common anode display respectively.
These are available from different vendors. They have a shape of the rectangular box similar to that of IC but in large size.
|Pin Number||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||common||Connected to Ground/Vcc based on the 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||Common||Connected to Ground/Vcc based on the 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|
Must Read 7 Segment Display Datasheet
Structural View of 7 Segment Display
From top view 8 segments can be seen in the form of numeral ‘8’.
Here, the 7 LED’s called segments are assigned with an alphabet from A to G. Forward biasing of the particular segment or LED will emit the light energy thus illuminating a part of numeral. There is another segment assigned as H, used for displaying dot.
The decimal or dot point is used for representing the decimal point in a numeral. For example, to display 5.5, the dot is used to represent the decimal point in this numeral.
Generally, in the LED package either all the cathodes or all anodes of the segments are combined to form a common pin. Thus each displays will have 7 pins used for displaying the digits, one common pin and another pin for decimal/dot point
Bottom view of the display is shown below. The bottom view of the segment shows 10 pins of the segment. These are cathode or anode pins of the LEDs present in the 7 segments. 7 segments are illuminated using these pins.
Internal Structure of 7 Segment Display
The internal structure of the display is too difficult. Internally, the device will have SMD LEDs. This can be divided into two parts i.e. internal circuit and the display. The internal circuit will have LEDs arranged in the rectangular form. These two parts are surrounded by glass, ceramics and plastic in order to protect them.
Working of 7 Segment Display
It works by glowing the required respective LEDs in the numeral. The display is controlled using pins that are left freely. Forward biasing of these pins in a sequence will display the particular numeral or alphabet. Depending on the type of 7 segments the segment pins are applied with logic high or logic zero and in a similar way to the common pins also.
For example, to display numeral ‘1’ segments ‘b’ and ‘c’ are to be switched on and the remaining segments are required to be switched off. In order to display two digits, two 7 segments are used.
Depending on either the common pin is anode or cathode, 7 segments are divided into the following types.
Types of 7 Segment Display
There are following two types of 7 segments.
- Common Anode (CA)
- Common Cathode (CC)
In common anode type, all the anodes of 8 LED’s are connected to the common terminal and cathodes are left free. Thus, in order to glow the LED, these cathodes have to be connected to the logic ‘0’ and anode to the logic ‘1’.
In order to display zero on this segment, one should enable logic high on a, b, c, d, e and f segments and logic low on segment ‘g’. Thus, the above table provides data on 7 segments for displaying numerals from 0-9.
As the name indicates cathode is the common pin for this type of 7 segments and remaining 8 pins are left free. Here, a logic low is applied to the common pin and logic high to the remaining pins.
Above truth-table shows the data to be applied to the 7 segments to display the digits. In order to display digit ‘0’ on 7 segments, segments a, b, c, d, e and f are applied with a logic high and segment g is applied with logic low.
7 Segment Display Features
- It is available in two modes i.e Common Cathode and Common Anode.
- Available in many different sizes like 9.14mm,14.20mm,20.40mm,38.10mm,57.0mm and 100mm (Commonly used/available size is 14.20mm).
- Available colours: White, Blue, Red, Yellow and Green (Res is commonly used).
- Low current operation.
- Better, brighter and larger display than conventional LCD displays.
- Current consumption: 30mA / segment.
- Peak current: 70mA.
- The applications of 7segments are mostly in digital calculators, electronic meters, digital clocks, digital clocks, clock radios, etc.
- Today most of the applications are using LCDs, because of low current consumption.
- Used in applications where font size is required to be bigger.
- Microcontroller Independent, hence used in small circuit projects.
- Used in combination with four segments to display measurement/sensor value with four characters.
- Has bright illumination, hence used where the display is required to work in low light or dark conditions.