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Author Topic: Why use this  (Read 769 times)

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Offline zabuza™Topic starter

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Why use this
« on: February 28, 2010, 06:09:15 PM »
why use a trimmer in this example below. i seen many circuits use a trimmer why not just a normal resistor?

http://www.societyofrobots.com/robotforum/index.php?topic=10437.0

Offline waltr

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Re: Why use this
« Reply #1 on: February 28, 2010, 06:45:20 PM »
There are a number of reasons:

First most is when the resistor value needed can not be calculated due to variance in the values of the other components. The pot is to adjust for the component variance. Trimming the input offset of an Op-amp is one case. Another is to match a number of simular circuits to respond the same to the same input stimulus (like the pot on each photo sensor in the linked circuit).

Second is when the designer either doesn't know how to calculate the exact resistor value needed or is unsure of what the circuit will actually do. I commonly do this when prototyping a new circuit I'm unsure of. I'll use the pot to characterize the circuit then use a fixed value resistor for the 'real' circuit unless the first reason exists.

Third is when the set-point that is needed is not known or needs to be set by the user, stereo volume control or an adjustment for the ambient light level.

Do these answers help?

Offline zabuza™Topic starter

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Re: Why use this
« Reply #2 on: February 28, 2010, 07:01:42 PM »
So how would this be used in a line following robot? surely by adjusting the pot you run the risk of blowing the ldrs

Offline Razor Concepts

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Re: Why use this
« Reply #3 on: February 28, 2010, 07:06:31 PM »
LDRs are just resistors. They will draw as much current as they need and no more. Adjusting the pot to 0 ohms would still not fry it, since there will always be at least 1k in front of them.

 


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