IC 555 is the most popular timer IC used in various applications. It is used both in analogue and digital circuits to generate short duration pulses. This single IC can be used in various modes like Monostable, Astable, Bistable, Schmitt trigger etc. It is important to know the internal details and working of this IC before using in a circuit. If it is not properly used, the result will not be satisfactory and there is chance for false triggering of the circuit.