7 Segment Display

It is the LED or LCD based display for showing the decimal numerals or letters in electronic devices such a meters and digital clocks. It consists of seven LEDs (LCD) which turn or off individually or combine to produce Arabic numerals. In the 7 segment display, the display segments are arranged obliquely for increasing the readability.

The seven segments are arranged as a rectangle consisting of two vertical segments on each side and three horizontal segments, one each on the top, middle and bottom. The segments are named by the letters A to G and the eighth segment is a Dot representing the Decimal point (DP).

Pin connections of 7 Segment display

Pins and Numerals displaying in the 7 segment display

There are two types of 7 Segment displays. In Common Cathode type the Cathodes of all the seven LED segments are connected together and brought to pins 3 and 8.Where as in Common Anode type all the Anodes are connected together and brought to the pins 3 and 8. To light a particular segment, the driver IC for 7 segment display should give positive voltage to anode pins (in common cathode type) or sink current (in common anode type).The diver gives current pulses with a short blanking interval to change the display from one another.

In numerical display, the 7 segment display shows numbers 0 to 9 and if the DP is connected, it lights after 9.

The segments of 7 segment display lighting to show numerals

Decoder IC

To drive the 7 Segment display, a decoder IC is necessary. Decoder IC converts one digital format into another. The most commonly used decoder is Binary Coded Decimal (BCD) to 7 segment decoder IC. ICs like 74LS47 produce numbers or Hex characters from 0 to 9 and A to F by lighting the correct combination of segments.

Connecting the Decoder with 7 Segment display