Timer555. - Here is. The classic differentiator circuit consists of a capacitor and resistor. In this way, the positive change in the trigger signal is coupled to the 555 via C2. When the trigger signal eventually resets, D2 is required to prevent the change in voltage from creating a substantial negative spike. While a negative transient of this nature is unlikely to cause damage, it could well cause temporary IC malfunction.
R-C timing circuit
C1 and the series resistance of R1 to R3 affect the timeout function. Circuit values may be selected per application requirements. This part of the circuit is fairly typical.
The Original Article : "Edge-Triggered 555 Monostable Multivibrator"