led

LED Light emitting diodes (LED) can be used as general-purpose indicators. When compared with conventional filament lamps they operate from significantly smaller voltages and currents. LEDs are also very much more reliable than filament lamps. Most LEDs will provide a reasonable level of light output when a forward current of between 5 mA and 20 mA is applied. Light emitting diodes are available in various formats with the round types being most popular. Round LEDs are commonly available in the 3 mm and 5 mm (0.2 inch) diameter plastic packages and also in a 5 mm × 2 mm rectangular format. The viewing angle for round LEDs tends to be in the region of 20° to 40°, whereas for rectangular types this is increased to around 100°. Spectral response Light of different colours can be produced by using different semiconductor materials in the construction of an LED. However, there is a wide variation in both the efficiency and light output of LED of different colours. For this reason, red displays tend to be most common (with a peak output at around 650 nm). Note that this is towards one end of the visible spectrum Seven segment displays LED displays are frequently used to display numerical data. The basis of such displays is the seven segment indicator which is often used in groups of between three and five digits to form a complete display. The arrangement of the individual segments of a seven segment indicator is shown in Figure.

Upload: pravin-hande

Post on 31-Jan-2016

215 views

Category:

Documents

0 download

Report

Download

Embed Size (px):

DESCRIPTION

LED

TRANSCRIPT

LEDLight emitting diodes (LED) can be used as general-purpose indicators. When compared with conventional filament lamps they operate from significantly smaller voltages and currents. LEDs are also very much more reliable than filament lamps. Most LEDs will provide a reasonable level of light output when a forward current of between 5 mA and 20 mA is applied. Light emitting diodes are available in various formats with the round types being most popular. Round LEDs are commonly available in the 3 mm and 5 mm (0.2 inch) diameter plastic packages and also in a 5 mm × 2 mm rectangular format. The viewing angle for round LEDs tends to be in the region of 20° to 40°, whereas for rectangular types this is increased to around 100°. Spectral responseLight of different colours can be produced by using different semiconductor materials in the construction of an LED. However, there is a wide variation in both the efficiency and light output of LED of different colours. For this reason, red displays tend to be most common (with a peak output at around 650 nm). Note that this istowards one end of the visible spectrum

Seven segment displaysLED displays are frequently used to display numerical data. The basis of such displays is the seven segment indicator which is often used in groups of between three and five digits to form a complete display. Thearrangement of the individual segments of a seven segment indicator is shown in Figure.

The segments are distinguished by the letters, a to g. Since each segment comprises an individual LED it is necessary to use logic to decode binary (or binary coded decimal) data in order to illuminate the correct combination of segments to display a particular digit. For example, the number ‘1’ can be displayed by simultaneously illuminating segments b and c whilst the number ‘2’ requires that segments a, b, g, e, and d should be illuminated. The circuit of a seven segment display is shown in Figure. whilst a typical decoder and decoder truth table are shown in Figures