Monostable Mode using IC 555
In this mode the 555 is used as a single-shot timer to produce an output of a fixed duration. The time period is set using one capacitor and one resistor. The time period is started by applying a low pulse to the trigger input. The output pin then goes high for the duration of the time period. The time period may be interrupted by applying a low pulse to the reset pin. If reset is not being used it is normally connected to the +ve supply. [....]
