Circuit Diagram Knowledge

This is the easy build active low trigger circuit based timer IC 555. The circuit also known as normally closed trigger circuit. 9V DC supply is required to operate this circuit.

This circuit sits Low and the output goes High after the push-button switch is pressed. When the normally-closed push button switch is pressed, it opens and the uncharged 1uF capacitor is going to be pulled to almost 0v rail via the 10k resistor and this will bring pin 2 Low for making output pin 3 High for the period decided by the 22uF capacitor and 100k resistor. If the push-switch continues open, the 1uF will charge via the 100k and at some point the output of the 555 will go low.

But generally the switch has to be pressed for a short period of time in order that the timing parts (100k and 22uF) make the output go High for a short time period.