7 Segment Display

 

Seven segment display is a device that can display decimal numbers and are widely used in electronic clocks, electronic meters, digital display panels and a hand full of  applications where numerical data is  is displayed. The idea of seven segment display is very old and they are in the scenario from early nineteenth century. Seven segment display have seven segments which can be individually controlled (ON/OFF) to display the desired number. Numbers from 0 to 9 can be displayed using  various combinations of the segments and in addition to this the hexadecimal letters A to F can be also displayed using a seven segment display. The seven elements (segments)  are arranged in the form of a square shaped “8″ which is slightly inclined to the right. The slight inclination to the right is given to improve the readability.Some seven segment displays have an additional dot element which can be used for indicating decimal points. The segments may be based on incandescent bulbs, fluorescent lamps, LCD or LED. Here in this article we give stress to the LED seven segment display.

In an LED 7 segment display, as the name indicates the 7 segments plus the dot segment are based on LEDs. When power is given to a particular segment, it glows and the desired digit can be displayed by powering the suitable combination of LEDs. LED seven segment displays are of two types, common cathode and common anode. In a common cathode display, the cathode of all LED segments are tied together as one common cathode pin and the anode terminals are left alone as input pins. In this scheme the common cathode is always connected to ground and the control signals (active high) are applied to the inputs (anode terminals) .In common anode type display, the anodes of LED segments are tied together as one common anode and the cathode terminals are left alone as input. In this configuration the common anode is always connected to a suitable positive voltage and the control signals (active low)  are applied to the inputs (cathode terminals).