ABSTRACT
LEDs are probably used more widely than any other device for indicating the output of a system. They are very efficient, use little current, last much longer than filament lamps, are less easily broken. They are made in a wide range of colours, shapes and sizes. They are also available with a built-in flashing circuit. Because they take little current, they can be driven directly from the output of a 7555 timer IC, TTL, CMOS buffer gates (4049 and 4050), microcontrollers and many other devices. This simplifies circuit design and construction. Their main disadvantage is that they are not easy to see when viewed in bright sunlight. However, really bright LEDs are being developed, so this will not be a problem in future.
