Dumb Potentiometer Question

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

Ok... i should really know this.... normally when i see a pot used, it's used like this:

Where from the top to the bottom it is the full max value of the pot (i.e. for a 5k pot, it's 5k), and on the right (with the arrow) is the variable lead of the pot.

Now.... on this pic....

I don't see how i'm supposed to wire the pot up. it just shows two sides... do i just connect to one side, and the variable point, and leave the other side open? I guess i'm just not understanding the schematic. It's direct off of the LM-317 datasheet at http://www.national.com/ds/LM/LM117.pdf if that helps you explain any.

Thanks in advance

2

Typically you tie one end to the wiper. This provides you with 2 leads.

here is a pic.

http://dev.emcelettronica.com/files/u4/Mechanical_Potentiometers.jpg

3

so... in the case of the schematic i posted, do you tie one end of the pot to gnd, then the swiper to adj/R1? or do you tie the swiper and one end of the pot together and tie that combo to (not sure, gnd or adj/r1) and the other end (not connected to the swiper) to the opposite side?

4

Here's what I think you're saying:

The one the left will work as well as the one on the right. I prefer the one on the right as unconnected terminals can act like antennas and pick up noise.

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5

Ahhh... so the output value is the same on your "left version" as your "right version", just that the "right version" is a cleaner way to do it?

6

Yes, in my opinion.

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7

Thanks! I'll give it a shot :slight_smile:

8

Also with the right version, if the wiper fails the connection doesn't go open circuit, this is sometimes important.

9

With the right hand circuit, if you need 5K Ohms in the circuit, wouldn't you need to use a 10K pot to get that 5K load with the two leads effectively putting the two resistance loads in parallel, or am I missing a trick here? (I assume of course that that is already factored into the circuit... )

10

Nope, the right-hand circuit is exactly equivalent in resistance to the left. If you want 5k you just put the pot to its half-way position.

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11

Yeah, ignore me... I was just adding to the thread dumb factor, lol :smiley: