This Project is very simple and when completed, causes a light-emitting diode (LED) to flash or pulse alternately on and off at a very slow rate, that is, at a low frequency. It could be used as a dummy car alarm indicator. You sometimes see these tiny pulsating lights in expensive cars protected by sophisticated car security systems, warning you that the car alarm is armed and ready.
For this design, the LED flashes on for a brief period and stays off for a relatively longer period. Because additional current is consumed from the battery every time the LED comes on, this long rest period conserves battery power. The brightness of the indicator LED is also limited, again in order to preserve battery power.
The 555 timer integrated circuit (IC) is configured in an oscillating mode that results in a continuous train of pulses being generated. The frequencydetermining components have been chosen to give a very slow pulse rate. Two resistors and a capacitor determine the flashing rate of the LED. Power is supplied from a 9-volt battery.