Led Flasher Circuit by 555 timer
This circuit is built around one of the most popular timer integrated circuits, the 555 timer.
This circuit will flash the led on and of at regular intervals.
From left to right, the two resistors and the capacitor set the time it takes to turn the led on or off, by changing the time it takes to charge the capacitor to trigger the timer. Next is the 555 timer, this is where all the work gets done to determine the time the led stays on and off. It contains a complicated circuit inside, but since it is packaged in the IC it can be used as a simple component.
Link : http://electroniccircuitsforbeginners.blogspot.com
