Chapter 5
Light Emitting Diodes (LEDs)
A LED is a tiny semiconductor light source, used mainly to indicate the status of electronic circuits, for example to indicate that power is applied to a circuit. The LED was invented in 1962 by Nick Holonyak while working at the General Electric Company. Early LEDs emitted low-intensity red light, but today high brightness and many colour LEDs are available. These LEDs are now used to replace incandescent and neon light bulbs in many energy efficient applications, for example LEDs are used as clusters in torches, automotive lights, traffic lights, signs and indicators, games, and so on. Infrared LEDs are used in most consumer remote control applications. LEDs offer many advantages over incandescent light sources, such as lower energy consumption, smaller size, longer lifetime, faster switching, available in many colours, low-voltage operation, do not get hot, and more robustness.
In this chapter we will review the various LED types used in microcontroller based applications, and also see how they can be used in electronic circuits. In addition, we will be looking at the basic principles of other commonly used LED based displays, such as single- and multi-digit 7-segment LEDs and alphanumeric LEDs.
