Monostable Multivibrators have only ONE stable state Called Mono, and produce a single output pulse when it is triggered externally. Monostable multivibrators only return back to their first original and stable state after a period of time determined by the time constant of the Rc coupled circuit here Transistor version.,
Monostable Multivibrators or “One-Shot Multivibrators” as they are also called, are used to generate a single output pulse of a specified width, either “HIGH” or “LOW” when a suitable external trigger signal or pulse T is applied. This trigger signal initiates a timing cycle which causes the output of the monostable to change its state at the start of the timing cycle and will remain in this second state.
The timing cycle of the monostable is determined by the time constant of the timing capacitor, C1 and the resistor, R1 until it resets or returns itself back to its original (stable) state.
The monostable multivibrator will then remain in this original stable state indefinitely until another input pulse or trigger signal is received. Then, Monostable Multivibrators have only ONE stable state and go through a full cycle in response to a single triggering input pulse.