Potentiometer Range

[vidarr]

I have a recycled potentiometer that I want to use on very simple 3.3-5v projects. Right now, I am only getting a range from 2.9v to 3.10v. I saw some tutorials of people scraping the pots to decrease the resistance, so maybe I could get up to (or closer to) the full 5v? But, I don't see a way to easily do that with the one I have.

Is there an easy way to do this another way? It can be very crude. I do not need precision here. I just need it for dimming LEDs, and for quickly prototyping simple stuff like that (real fast without using PWM).

Thank you!

[ataradov]

Potentiometers don't have voltage ranges. Show us how you use it.

[vidarr]

Like this pic.

[vidarr]

I saw another schematic with a resistor in parallel with the LED after the pot. I did not try that yet.

[ataradov]

And what voltage do you measure? And what is the value of a fixed resistor? What is the battery voltage?

Variable resistor typically go from 0 OHm to their nominal value. Shaving them can only increase the nominal value.

[ataradov]

Also keep in mind that LED are driven by the current, not the voltage.

[Richard Crowley]

I saw another schematic with a resistor in parallel with the LED after the pot. I did not try that yet.

THAT circuit makes NO SENSE AT ALL.
DO NOT use that circuit for ANYTHING.
Unless you want to blow up the LED and/or the pot.
You still have not shown us your circuit with "a range from 2.9v to 3.10v"?

[Zero999]

The voltage across the LED will vary very little as the current is changed, as they have a fairly constant voltage, irrespective of current,

[vidarr]

I redid everything a couple more times. Whatever happened the first times, I could not repeat again exactly the same (I got +/- 0.7v max). I was having a fluctuation of about 0.20v, but no change in LED brightness. Pretty sure it was a short somewhere.

I took everything completely apart and changed leads. Now, I am getting steady voltage while turning the pot. The LED goes from from "full" bright to almost off. The volts only go from 3.30 to 3.29. This is what I wanted.

Somewhere along the way, I was reading some bad info (wrong words?) as to what is happening here (EDIT: along with a faulty setup). I knew what I wanted to do -- the results; I just need to learn all the technical English. I still don't understand the potentiometer fully. I get this analogy of the "wiper" I think. In my head, I just see a resistor that gets more or less resistant (bigger/smaller, stronger/weaker, etc). If you know some simple English explanation that would be great. I watched a bunch of videos on YT. I need the explanation that pops in my head.

Thank you.

edit: I changed my location setting too. I think the USA was confusing people. Now you know my issues... LOL

[Nusa]

https://en.wikipedia.org/wiki/Potentiometer

This may be about the right level for you:
https://learn.sparkfun.com/tutorials/voltage-current-resistance-and-ohms-law/all

[Richard Crowley]

Discussing an unknown circuit using words is almost useless.  That is why we have schematic diagrams.
Unless you can show us a schematic diagram of your test circuit, AND WHERE you are measuring the voltage, it doesn't mean much to us.

There are plenty of resources about potentiometers available online.
I spend a few quality milliseconds with Google and found hundreds.
Here are a couple of the better examples I saw after a quick review...

https://www.electricaltechnology.org/2015/01/resistor-types-resistors-fixed-variable-linear-non-linear.html#121_potentiometers

https://en.wikipedia.org/wiki/Potentiometer

A potentiometer does NOT control voltage or current.  It only controls resisistance.
It COULD control voltage or current depending on how you connect it in a complete circuit.
But when it comes down to Ohm's Law, a potentiometer is just like any other resistor.

If you only connect between the "start" and "end" of the resistance, it is just like a fixed resistor.
Except that you can change the resistance between each end and the wiper.
And a potentiometer is effectively TWO resistors.
One resistor between the "start" and the "wiper",
and the other resistor between the "wiper" the "end" of the pot.

[amyk]

Note that most potentiometers are not meant to pass large currents, and can be easily damaged if you do that --- ones which are, are usually called rheostats instead.

[vidarr]

Thanks guys! Both the EE Library and Sparkfun links are great. The library link is especially awesome for me.

[vidarr]

Is this a rheostat? I inherited it from my wife's dad.

[ataradov]

This is air capacitor.

[vidarr]

Interesting... I use it on my desk to keep the air from blowing my papers away.

[AngraMelo]

Hello my friend,

I think it would be rude of me to answer you in Portuguese given that we are in a english forum.
Im also a beginner but I believe I can help you.

If you need assistance with that experiment email me at: thiagomelogomes@yahoo.com.br

[tooki]

I have a recycled potentiometer that I want to use on very simple 3.3-5v projects. Right now, I am only getting a range from 2.9v to 3.10v. I saw some tutorials of people scraping the pots to decrease the resistance, so maybe I could get up to (or closer to) the full 5v? But, I don't see a way to easily do that with the one I have.

By the way, scraping the conductive trace in a potentiometer would increase its resistance, not decrease it.

[rstofer]

Interesting... I use it on my desk to keep the air from blowing my papers away.

Don't damage it and don't lose it!  Those air capacitors are rare and valuable.  They were used for changing the frequency of radios and such.

[ataradov]

Those air capacitors are rare and valuable.

I would argue the valuable part.

[Richard Crowley]

Those air capacitors are rare and valuable.

I would argue the valuable part.

Valuable perhaps for people working on vintage circuits (i.e. using firebottles)
But yes, modern solid-state circuits don't depend on such vintage parts like those capacitors.

[Nusa]

Those air capacitors are rare and valuable.

I would argue the valuable part.

Agreed. The ebay value would probably be under $10. They generally outlive the devices they were used in, so besides takeouts, you can even find some parts stock from over 50 years ago, still in boxes.

They're simple enough that an amateur can specify and make their own, if they really want to. The how-to information is out there, if you look.

[vidarr]

I am going to hide that air capacitor now -- that is R$40 here. Just kidding. But seriously, you could get shot for less than $10 here. Actually, you can get shot for free.

No, but seriously, I was waiting to think of something cool to do with it. Just nothing "steam punk". I broke my only nixie tubes and do not have any aviation goggles to wear.

I got a bunch of old stuff her from her dad. He was an electrical engineer. The problem is, my wife and her mom think it is all junk. They are throwing it away slowly. He has rooms and rooms full of stuff. There is nothing I can do. They won't let me touch anything. I looked into the rooms one day when I had access to the keys and I almost peed my pants how much cool stuff was there. I try not to think about it.

I got a vintage Syder amplifier that was the best stereo amp in all Brazil during the military dictatorship (ok, not best, only amp). There is more, but I want to post here some stuff another time about some project ideas I have from some of this stuff I was able to save.

[vidarr]

Here is the Spyder. I took apart to clean and troubleshoot. Her dad cut the transformer out. Everything I have here that doesn't work has a broken transformer.

Notice the green and yellow wires and wrap. Green and yellow were the dictator's favorite colors. Everything had to have green and yellow or it was banned, confiscated and could not be sold. They told us green and yellow are the best and only colors in the world. I don't know why they told us in school that, it is totally obvious. That is why whenever you see Brazilains, everything is green and yellow. 

[vidarr]

Bigger.