By forward biasing different LEDs we can display the digits 0 through 9. For example, to display a zero, the LEDs A, B, C, D, E and F are forward biased. To light up a 5,
we need to forward bias segments A, F, C, C, D. Thus in a seven segment display depending upon the digit to be displayed, the particular set of LEDs is forward biased. The various digits from 0 to 9 which can be displayed using seven segment display are shown in the Fig.
Types of Seven Segment Display
The two types of seven segment display are available called,
1) Common anode type
2) Common cathode type
Common Anode Type
In this type, all anodes of LEDs are connected together and common point is
connected to + V which is positive supply voltage. A current limiting resistor is required i be connected between each LED and ground.
Common Cathode Type
In this type, all cathodes of LEDs are connected together and common point
is connected to the ground. A current limiting resistor is connected between each LED and the supply + Vcc. The anodes of the respective segments are to be connected to + for the required operation of LEDs.
LED Driver Circuit
The output of a digital circuit is logical i.e. either 0 or 1. The ‘0’ means low
while 1’ means high. In the high state the output voltage is nearly 5V while in low
state, it is almost OV. If LED is to be driven by such digital circuit, it can be connected as shown in the Fig. 4.21. When output of digital circuit is high, both ends
of LED are at 5V and it can not be forward biased hence will not give light. While when output of digital circuit is low, then high current will flow through LED as it becomes forward biased, and it will give light.