Why do you need multivibrators to create a pulse?

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Discussion Overview

The discussion revolves around the necessity of using multivibrators, specifically mono-stable multivibrators, to create pulse signals in electronic circuits. Participants explore the practicality of simpler circuit designs versus integrated circuits for generating pulses in response to external triggers.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the complexity of using a mono-stable multivibrator, suggesting that a simple circuit with resistances and voltage sources could suffice to create a pulse.
  • Another participant explains that a mono-stable multivibrator achieves the desired functionality and mentions specific integrated circuits like the 74C221 or 74HC221 that simplify the design.
  • A participant proposes the idea of using a mechanical switch to create pulses, arguing it might be easier than using electronic components.
  • In response, another participant acknowledges the feasibility of mechanical solutions but emphasizes the advantages of integrated circuits for producing reliable and varied pulse durations.
  • Concerns are raised about the reliability and efficiency of mechanical systems compared to solid-state electronics, with one participant detailing the limitations of mechanical timing elements.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and effectiveness of using integrated circuits versus simpler or mechanical solutions for pulse generation. No consensus is reached regarding the superiority of one approach over the other.

Contextual Notes

Participants highlight various assumptions about reliability, efficiency, and the complexity of circuit designs without resolving the underlying technical considerations or limitations of each proposed method.

Who May Find This Useful

This discussion may be of interest to electronics enthusiasts, students studying circuit design, and professionals exploring different methods of pulse generation in electronic systems.

jd12345
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A mono-stable multivibrator is used to create a pulse in response to an external trigger. Why do you need such a complicated circuit for that?

Can't we have a simple circuit with resistances and voltage sources. Whenever there is an external trigger something completes the circuit(earlier the circuit was open) and hence current flows through thus creating voltage across the load. Now the circuit automatically opens after sometime(through some mechanism).
So this way a pulse is created across the load resistance right?
 
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A mono stable behaves in much the same way as you describe, except that the "something" you suggest is achieved with the mono stable circuit.

You can get integrated circuits which contain mono stables and reduce the additional components to a minimum.

A useful IC is the 74C221 or 74HC221. These contain two mono stables and require very few additional components to function.
 
Can't we have a mechanical switch so that it closes when there is an external trigger and then opens after sometime. That's much easier to make rather than all the op-amps, capacitors etc. right?
 
Sure.
Such arrangements are often used.
Suppose you have a water tank. You could detect when the water level drops to a certain level then turn on the water supply for some exact time the top up the water level.

However, using an integrated circuit is no big deal and often the best way to produce a long pulse from a short one or vice versa.
 
I'm still not comfortable. Could you tell me why the integrated circuit is the better way?
 
jd12345 said:
I'm still not comfortable. Could you tell me why the integrated circuit is the better way?
Mechanical contrivances are way too slow, too noisy, and use too much power to provide a general solution for one-shot pulses in electronics. They can be built using a clock spring to furnish the timing element for durations of a few seconds to an hour or so. With the passage of time the spring will stretch a bit, causing the duration to change, and eventually the spring may break. Solid state electronics elements are usually far more reliable (though of course a poorly designed circuit may still fail), and extremely versatile: one good circuit can offer pulses with durations anywhere from microseconds to kiloseconds.
 
Thank you very much. I guess that is what I was looking for.
 

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