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 ...

The 555 adjustable timer circuit ... green LED turns OFF, the red LED turns ON and the beeper sounds. The time period is set by adjusting the variable resistor. It can be adjusted from 1 to 10 minutes ...