This is a small size led flasher built with the 555 timer IC that is powered from 2 x 1.5V batteries. The circuit can be used as a flashing metronome, dark room timer, memo-reminder or other similar applications.
Schematics of LED Flasher with the 555 timer IC
how does the 555 flasher circuit works?
The IC is connected as a astable multivibrator with a duty cycle of about 10%.
In figure 1 the LED will be ON for a short period of time and OFF for a longer period. The duty cycle can be reversed if the LED is connected as shown in figure 2 but the battery consumption will also increase due to the fact that the LED will stay ON for a longer period of time. in figure 3 for a variable flash rate, replace the 220k pot with a 220k in series with a 22k resistor. And that is a simple 555 led flasher circuit.