Most useful Timer IC 555 is widely used as a Monostable Multivibrator that generates a single output pulse for a specific duration when triggered. This output Pulse Duration is depends on the Timing Resistor (R) that is connected between Discharge pin (7) and bias. Then Timing Capacitor (C) that is connected between Threshold pin (6), Shorted Discharge pin (7) and to Gnd supply. By varying this element value we can change the output pulse duration. Here is the Simple IC 555 Timer Monostable Multivibrator Calculator to calculate either R, C or Pulse Duration.
555 Timer Monostable Multivibrator Calculator
The Formula used by this calculator to calculate Output Pulse width Time is
T = 1.1 * R * C
When the Falling Edge Detected by the Trigger Pin (2) Then the Circuit Starts to Produce One pulse width Time depends on the R C element values. This is call one Shot or Monostable. This cycle continues whenever the trigger pin gets signal.
This IC 555 Timer Monostable Multivibrator circuit is Constructed by using Timing Resistor R (Unknown) and Timing Capacitor C (Unknown). You can choose any value depends on you output pulse width Time need. Other than this components there is Pullup Resistor and Trigger switch. When you press the Trigger switch the Trigger pin (2) gets short pulse, that enables Timer IC to Oscillate single pulse.
IC 555 Pinout
As you can see the Trigger pin enables Comparator and Flip flop to Oscillate one Single pulse depends on the R and C connected with Discharge and Threshold pin.