One-shot (monostable) timing In a standard one-shot multivibrator (monostable), the output pulse width is primarily determined by which external timing elements?

Introduction / Context:
A one-shot, or monostable multivibrator, produces a single pulse of controlled width in response to a trigger. Designers frequently need to set this pulse duration to meet interface timing, debounce inputs, or generate timeouts. Knowing which components control the timing is essential when selecting values or troubleshooting errant pulse widths.

Given Data / Assumptions:

• Device: generic one-shot (for example, 74121/74122 or CMOS variants).
• External timing network present on pins labeled REXT and CEXT.
• Pulse width depends on the RC time constant scaled by device-specific factors.

Concept / Approach:
Most monostables charge or discharge an external capacitor through an external resistor. The internal comparators and reference levels detect when the capacitor voltage crosses certain thresholds, ending the pulse. Thus, the dominant factor in pulse width is the product R * C, often multiplied by a constant K determined by the IC family and operating conditions.

Step-by-Step Solution:

Verification / Alternative check:
Bench measurement of the pulse width with an oscilloscope should closely match tW calculated from the chosen R and C, within tolerance bands. Simulation with SPICE models can also confirm expected timing before hardware build.

Why Other Options Are Wrong:

• Two resistors / two capacitors: Without both R and C together, a monostable cannot set a stable, finite pulse width based on RC charging behavior.
• None of the above: Directly contradicts the standard monostable design, which always relies on an RC network.

Common Pitfalls:
Using incorrect units (for example, confusing nF and µF) or misreading the device-specific constant K, leading to an order-of-magnitude timing error.

Final Answer:
a resistor and capacitor