Just push the switch and the timer will start. When timer finishes, the LED glows.
Change the timer value by changing Resistance R
Timer value=R*1.1*(10^-3) seconds
Here timer value (20sec) is nothing but escape time.
This type of timer is used in bomb circuits, where planter triggers the circuit and starts to run. He has just 20sec to flee away. This time is called escape time.
