Seven segment displays are the output display devices that provide a way to display information in the form of image or text. For displaying the images or text in a proper manner, some types of  displays can show only alphanumeric characters and digits. But, some displays can also show characters and images. Most commonly used displays along with the microcontrollers are LCD, LEDs and seven segment displays,etc.

Seven Segment Display

The seven segment display is the most common display device used in many gadgets, and electronic appliances like digital meters, digital clocks, microwave oven and electric stove, etc. These displays consist of seven segments of light emitting diodes (LEDs)  and that is assembled into a structure like numeral 8. Actually seven segment displays contain about 8-segments wherein an extra 8th segment is used to display dot. This segment is useful while displaying non integer number. Seven segments are indicated as A-G and the eighth segment is indicated as H. These segments are arranged in the form of 8 which is shown in the seven segment display circuit diagram.

A seven segment displays are generally available in ten pin package. In that 8 pins relate to the 8 LEDs, the remaining pins at middle are internally shorted. These segments come in two outlines they are common cathode and common anode. In common cathode configuration, the negative terminals are connected to the common pins and the common is connected to the ground. When the corresponding pin is given high,then particular LED glows.In a common anode arrangement, the common pin is given to a logic high and the pins of the LED are given low to display a number.

Seven Segment Display Working

When the power is given to all the segments, then the number 8 will be displayed. If you disconnect the power for segment G (that means 7) then that will result number 0. The circuit of the seven segment display is designed in such a way that the voltage at different pins can be applied at the same time. In the same way,  you can form the combinations to display numerals from 0 to 9. Practically, seven segment displays are available with two structures, both the type of displays consists of 10 pins.

The numeric seven segment displays can also display other characters. But generally A-G and L, T, O, S and others are also available. Some problems may occur with the H, X, 2, and  Z. Anyways the common seven segment display is numeric only. Alphanumeric displays are also available but cost is little more. These types of displays still have a real purpose due to its high illumination and 7 segment displays are used in dark areas like railway stations. Even 7 segment display based countdown display is used in NASA, which can be read easily even in sunlight.

• Common Anode Display

• Common Cathode Display

Common Cathode 7-segment Display

In this type of display, all the cathode connections of  the LED segments are connected together to logic 0 or ground. The separate segments are lightened by applying the logic 1 or HIGH signal through a current limiting resistor to forward bias the individual anode terminals a to g.

Common Anode 7-segment Display

In this type of display, all the anode connections of the LED segments are connected together to logic 1. The separate segments are lightened by applying of  the logic 0 or LOW signal through a current limiting resistor to the  cathode of the particular segment a to g.

Therefore, common anode seven segment displays are very popular as many logic circuits can sink more current than they can source. These displays are not a direct replacement in a circuit for a common anode display, as  it is the same as connecting the LEDs in reverse, and hence the light emission will not take place. Depending upon the decimal number displayed, the particular set of LEDs is forward biased. For instance, to display the numerical number 0, we need to light up remaining segments corresponding to a, b, c, d, e and f. Then the digits from 0 through 9 can be displayed using a seven segment display.

Seven Segment Display Controlling Ways:

There are different types of controlling techniques that are implemented by interfacing these seven segment displays with the external controlling devices. Seven segment displays must be controlled by other external devices. Different types of microcontrollers are very useful to communicate with external devices like keypads, memory, switches, etc. There are numerous interfacing techniques that have been developed to solve the complex problems to communicate with displays.