Potentiometers or pots as well as trimmers and rheostats
are frequently confused as they're very similar.
But don't stress about it too much people,
know what you're talking about most of the time
though more precision and language will help.
So, a potentiometer or trimmer is usually referring to a voltage divider.
Now, potentiometers are usually bigger
and easy to adjust, so it's for things
where you anticipate, wanting to change it frequently.
Whereas when you get a trimmer,
Typically refer to things that are smaller and flatter
and you typically have to have a screwdriver to adjust it
But internally, it's about the same.
Rheostats are usually the same thing as pots or trimmers physically
But are called rheostats when they're acting
as variable resistors instead of voltage dividers.
So to keep things simple, I'll refer to all of them
as potentiometers or pots from here on now.
So, there are a couple of different symbols that are used
but all of them have three connection points.
I'm gonna use this slightly larger potentiometer
as a good example and that is,
you typically have an input and output and then a wiper
and they can be in different areas
and they can have different names as well.
It could be terminal 1 or terminal A,
terminal 2 or B or a wiper terminal.
So there's a bit of variation in the language that's used
but almost always, there are three connection points
as you can see on this potentiometer
and even on this trimmer, you can see just three plugs.
So, potentiometers what is happening is
as you're turning it, you are getting
either linear or logarithmic change
in the resistance between the different points.
Now, I say linear or logarithmic,
the difference between the two is called the taper
and that is really how much you change this
versus how much the output changes.
Now that may seem strange like
Why would I ever want anything that's not linear?
Why would I want something that's logarithmic?
But the time when you'd want something this logarithmic
is when you're dealing with something
like sound or brightness
whereas a doubling of sound
and a doubling of brightness
does not double our sensation of it. It's logarithmic.
So you have to go ten times brighter for us
to see basically a doubling of the brightness.
So that's where logarithmic potentiometers
and trimmers are great.
So this potentiometer actually has a linear taper
and I want to show, I have one hooked up here
to two multimeters and they're
both sharing the center terminal.
So as I change the potentiometer,
you will see how it changes from
currently, I have 1.4, 1.3 Ohms on one
and then almost 10 kilo Ohms on the other.
As I turn it, the one on the left,
the fluke just jumped up to 1
and the one on the right is now 9
and you will see that the resistance
between the center terminal
and the outside terminals is changing
and it's almost like they're giving
the other one that resistance
and I'll show you why physically that is happening later.
But the one on the left went from
practically zero resistance to as I go all the way up
It'll go all the way up to 10 kilo Ohms
or is the one on the right which started at 10
is now down to 1.2, 1.3 Ohms
And so that is what happens
with a linear potentiometer.
Is that you can see as you twist it, the resistance
that is seen by these ohm meters changes.
So what's happening there is
I have this one I took it apart
it's actually these things are pretty darn simple
And what is going on, there's only really four pieces
that come apart easily on this
and then another piece that I guess you could
technically say is a separate piece.
So five pieces total to this entire thing.
So you can see right here, this is the top part
and you have the plastic knob that comes out
It's got a little bit of grease in there
just to make it so it slides properly
and then this interesting contact point
which makes a lot of sense once we look at the bottom
But then we just have that
and that's just an enclosure to hold it together.
Now all this makes a lot more sense
once we look at this right here.
I almost feel like I should be using some
There we go here and this is better to point with
So, this spot right here is highly conductive.
This spot right here is highly conductive.
Whereas this black section is not quite as conductive.
It's very specific conductance like
I think you can assume that the entire thing
from here to here is about 10,000 ohms
and then as the wiper slides around the outside,
it changes the conductance
or the resistance of the entire potentiometer
and then the other side is going through more or less
depending on what the first side is doing
So, it's kind of interesting how that all works
The one in the middle, that's a constant
low resistance material right there
and then as the wiper, right here,
as these points slide along here
it changes the internal resistance
and that is how a physical potentiometer
or trimmer works
which is pretty interesting.
Now if we are to look at other things,
there are such things as digital potentiometers
and all that is basically,
they get a bunch of resistors put together
and then you say, all right I want this resistance
and it'll close switches or open switches
to get the resistance that you want.
So all that is there an array of resistors
of sometimes the same values,
sometimes different values
and then they open and close switches
to give you exactly what you want.
So that's how a digital potentiometer works.
So those are the two types of potentiometers
and trimmers that you have
are the mechanical where you physically sliding around
and then the digital which is literally
just opening and closing of switches.
So that's it, that's our basic overview
of potentiometers and trimmers.
I hope you found that interesting.
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