Monostable using 555

A Monostable Multivibrator, often called a one-shot Multivibrator, is a pulse-generating circuit in which the duration of the pulse is determined by the RC network connected externally to the 555 timer. In a stable or standby mode the output of the circuit is approximately zero or at logic- low level. When an external trigger pulse is obtained, the output is forced to go high upto V CC ). The time the output remains high is determined by the external RC network connected to the timer. At the end of the timing interval, the output automatically reverts back to its logic-low stable state. The output stays low until the trigger pulse is again applied. Then the cycle repeats. The Monostable circuit has only one stable state (output low), hence the name monostable. Normally the output of the Monostable Multivibrator is low. When the power supply V CC is connected, the external timing capacitor ‘C” charges towards V CC with a time constant (R A +R B ) C. During this time, pin 3 is high (≈V CC ) as Reset R=0, Set S=1 and this combination makes Q =0 which has unclamped the timing capacitor ‘C’.