Question 1

Definition scope: “A multivibrator is a circuit that toggles between two digital levels, either free-running (continuous) or on demand (triggered).” Assess this statement.

Accepted Answer

Introduction / Context: Multivibrators are foundational timing circuits in digital and mixed-signal electronics. They appear in three canonical forms—bistable, monostable, and astable—and underpin clocks, pulse stretchers, debouncers, and many other functions. This item checks a clear conceptual definition spanning these modes. Given Data / Assumptions: Bistable: two stable states (e.g., flip-flop). Monostable: one stable state; produces a pulse when triggered (one-shot). Astable: no stable states; oscillates continuously (free-running). Concept / Approach: The essence of a multivibrator is the controlled switching between logic levels. In the astable case, this occurs autonomously, generating a square or rectangular waveform. In the monostable case, a trigger causes a temporary excursion (a pulse) before returning to the stable state. The bistable case toggles states on demand and stays until another trigger. The statement’s wording correctly captures “continuous, free-running” (astable) and “on demand” (monostable/bistable) behavior. Step-by-Step Solution: Identify free-running behavior → astable multivibrator.Identify triggered one-pulse behavior → monostable (one-shot).Identify triggered toggling between two states → bistable flip-flop.Conclude that multivibrator encompasses these behaviors; the description is accurate. Verification / Alternative check: Textbook definitions group monostable/astable/bistable under “multivibrator” families, each with characteristic waveforms and timing components (RC networks, Schmitt triggers, 555 timers, or logic feedback networks). Why Other Options Are Wrong: Incorrect: Conflicts with standard categorization. Only true for astable / monostable: The term covers all three classic types, not one exclusively. Common Pitfalls: Thinking “multivibrator” means only oscillators (astable), ignoring monostable/bistable forms; confusing “on demand” (triggered) with level-sensitive gating. Final Answer: Correct

Question 2

Terminology check for monostable multivibrator: “A monostable multivibrator is commonly called a two-shot.” Determine if this usage is correct.

Accepted Answer

Introduction / Context: Precise terminology matters in digital electronics. Monostable multivibrators are ubiquitous for pulse generation, stretch, and timing intervals. Misnaming them can lead to confusion when selecting parts or reading schematics and datasheets. Given Data / Assumptions: Monostable has one stable state; a trigger produces a single output pulse of defined width. Common nickname used in industry: “one-shot.” “Two-shot” is not the accepted term for a monostable device. Concept / Approach: The name “one-shot” directly reflects behavior: one trigger → one pulse. “Two-shot” would imply two pulses per trigger or two stable states, neither of which describes a monostable. Bistable devices do have two stable states, but they are not called “two-shot.” Therefore, calling a monostable a “two-shot” is incorrect. Step-by-Step Solution: Monostable: one stable state → one output pulse per trigger.Bistable: two stable states → latches/flip-flops; not “shots.”Astable: free-running oscillator; continuous toggling.Conclude: accepted term for monostable is “one-shot,” not “two-shot.” Verification / Alternative check: Datasheets for 74121/74123 explicitly describe “monostable multivibrator (one-shot)” and never use “two-shot.” Application notes reinforce this naming convention across logic families and the 555 timer used in monostable mode. Why Other Options Are Wrong: Correct: Contradicts long-standing terminology. Correct only when cascaded / retriggerable: Cascading or retriggering changes pulse width or repetition, not the fundamental name. Common Pitfalls: Confusing “two stable states” (bistable) with “two-shot”; assuming retriggerable implies multiple shots per single trigger (it extends or restarts the pulse but does not rename the device). Final Answer: Incorrect

Multivibrators and 555 Timer Questions