Identifying the Free One-Shot Circuit

A "one-shot circuit" is a type of electronic circuit that produces a single output pulse when triggered by an input signal. The term "free" in this context usually implies a circuit that returns to a default state automatically after the pulse, or it might be interpreted as a circuit that generates a single event (pulse) from a trigger. Let's analyze the options:

• Schmitt trigger: This circuit exhibits hysteresis and is used for noise reduction or converting signals. It doesn't produce a single timed pulse.
• Monostable multivibrator: This is also known as a "one-shot" multivibrator. It has only one stable state. When triggered, it transitions to a temporary unstable state for a specific duration (determined by circuit components like resistors and capacitors) and then automatically returns to its stable state, producing a single output pulse. This perfectly matches the "one-shot" description.
• Astable multivibrator: This circuit has no stable states and continuously oscillates between two unstable states, producing a square wave. It's not a one-shot circuit.
• Bistable multivibrator: This circuit has two stable states. It requires two triggers to switch between states and remains in the triggered state indefinitely until another trigger arrives. It's commonly known as a flip-flop and is used for memory. It doesn't produce a single timed pulse automatically.

Therefore, the monostable multivibrator is the circuit referred to as a free one-shot circuit because it generates a single, timed output pulse upon receiving a trigger and then returns to its stable state.