Combining Three potentiometers resistance

Hello,

I am trying to connect three potentiometers (100, 100k, 2.5M) in series.
Point is that I would be able to change resistance in that range somewhat precisely. The problem is that either, it is completely dumb and unobtainable wish or that I am doing something wrong. I tried to connect two 100 pots in series, by my understanding, total resistance of them could be set up to approx. 200 Omhs, but all I get is 100.
Question: Is the first idea obtainable? If yes, how do I connect potentiometers in that way?

I tried to connect two 100 pots in series, by my understanding, total resistance of them could be set up to approx. 200 Omhs, but all I get is 100.

That's "impossible" unless the pot is adjusted wrong or defective.

If you just want a variable resistance you just use two of the three terminals. The wiper (center) and one end.

Question: Is the first idea obtainable? If yes, how do I connect potentiometers in that way

There's a possibility that the 2.5M and/or 100K resistors don't go down to 100 Ohms, so check the actual minimum, depending on how low you need to go.

How exactly are you connecting the 3 terminals of each pot and where are you measuring the resistance? A simple diagram would work better than words.

Steve

Assuming you're trying to read the final resistance with an Arduino, I'd use three identical pots and connect them to independent analog inputs. Three 10k pots will do great this way. In software you then interpret the coarse/mid/fine tuning of the three to come to a total - in effect you can create a 30-bit resolution, though I'd want some overlap between them, so a 24-bit overall resolution makes more sense. This should be enough for most practical purposes anyway.

If this is not what you're looking for, describe your complete project for better recommendations.

bugaiev12:
Hello,

I am trying to connect three potentiometers (100, 100k, 2.5M) in series.
Point is that I would be able to change resistance in that range somewhat precisely.

Standard carbon-track pots are very imprecise things, expecting that adding 100 ohms
variation to the value of a 2.5 megohm pot is going to be visible above the natural
fluctuations of the 2.5M contact point is "optimistic" shall be say.

I think you are either wanting a precision decade resistance box (expensive), or a 10-turn
precision cermet potentiometer.

Since you are a newbie , we need a schematic showing EXACTLY how you wired them because we cannot make
assumptions, given the nature of your question. Obviously it is unlikely you have found a way around Ohm's Law
so we can easily calculate the series or parallel resistance of pots in series or parallel. The fact that your results
are not consistent with what the math says, we must therefore assume you are wiring it incorrectly.
Please draw the schematic on a blank sheet of printer paper with a black ball point pen, photograph it with your
cell phone and post the photos using "Add attachments" link below.

You cannot wire three potentiometers in series and have a true potentiometer, that is one that operates as a voltage divider with one output that adjusts between zero and the input voltage.

But, you can create a variable resistor or reostat that can be adjusted between 0 to 2.66 megohms in total resistance by putting the three devices in series using either end and the center contact of each pot.

Google “difference potentiometer and reostat”

One is not equal to the other. Two different purposes. If you need three pots, the solution was in post #3.

"
You cannot wire three potentiometers in series "

100% true unless they are all wired as rwo wire rheostats with the wiper tied to one of the terminals and no wiper for the gruop but even then it probably wouldn't be practical but there's no question that all three pots would change the total resistance between the two end terminals. Conversely you could wire three pots in parallel and
short all the wipers together creating a 'pot bus' that is the mathematical sum of the three. Neither approach is found in the real world for a variety of reasons. I you want precision you should find another way. Electrically both will vary the output voltage.

bugaiev12:
Hello,

I am trying to connect three potentiometers (100, 100k, 2.5M) in series.
Point is that I would be able to change resistance in that range somewhat precisely. The problem is that either, it is completely dumb and unobtainable wish or that I am doing something wrong. I tried to connect two 100 pots in series, by my understanding, total resistance of them could be set up to approx. 200 Omhs, but all I get is 100.
Question: Is the first idea obtainable? If yes, how do I connect potentiometers in that way?

At what potentiometer terminal do you want to measure how much resistance?
Can you post a diagram of how you connected them and how/where you measured the resistance you got.
Are you trying to make a variable resistor that you can adjust from 0R to (100R + 100k + 2.5M) == 2,600,100R ?
OR
Trying to make a potentiometer?
There is a big difference.
Thanks… Tom… :slight_smile:

I'm afraid the OP is turning into yet another one post wonder.

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.