Dumb Potentiometer Question

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

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

here is a pic.


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?

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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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?

Yes, in my opinion.

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

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

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... )

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