Page 1012 - Basic Electrical Engineering

A simple on/off display using an LED is shown in Fig. 14.49. When the
supply is on, the LED will get supply and will be forward biased. A
resistance R is connected in series to limit the current through the LED. T is a

step-down transformer. Thus, the LED will show on/off status of supply.

Figure 14.49 An LED used in on/off display of power supply

There are a number of advantages of LEDs to be used in display devices.

They are compact, are illuminated very quickly, light intensity in them can be
controlled by varying the applied voltage, are available in different colours,

are quite simple, and are cheap.

14.13.3 Seven Segment Displays

A seven segment display board using seven LEDs is most widely used in

display devices in the field of electronics and instrumentation.
Some LED displays, you might have noticed in control panels, calculators,

mobile phones, electronic digital instruments, digital watch, etc. the LEDs are
very minute structures. Often plastic light pipes are used to enlarge the

lighted area as shown in Fig. 14.50. Display of digits ranging from 1000 to
1999 can be made on the display board by illuminating the segments in a

particular order.