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Topic: Question on potentiometers (Read 528 times) previous topic - next topic

AdmiralCrunch

Hi,

I'm new to all this and as I looked at some tutorials I bought the same potentiometers used in those.. this were 10K linear potentiometers..

now I would like to make a bigger project and need a ton of them, so I search on ebay and amazon to compare prices.. and I noticed some specifications I don't understand btw. I have questions on:


1)
the potentiometers I used are 10K .. but there are also ones with other resistance..
can I use them all?
what do I have to consider if I take a other potentiometer with a other resistance-value?

2) there is this value "Tolerance" .. what does that mean?

3) how are those one named, thich pins are bend 90° ? (example)

4) I saw there are potentiometers with different pin length.. is it just to fit the caps, or are there other defferences I should know?

MarkT

Hi,

I'm new to all this and as I looked at some tutorials I bought the same potentiometers used in those.. this were 10K linear potentiometers..

now I would like to make a bigger project and need a ton of them, so I search on ebay and amazon to compare prices.. and I noticed some specifications I don't understand btw. I have questions on:


1)
the potentiometers I used are 10K .. but there are also ones with other resistance..
can I use them all?
what do I have to consider if I take a other potentiometer with a other resistance-value?
EMI/noise (greater for larger resistance), power loss, heat dissipation (greater for smaller resistance - you can
calculate this)
Quote
2) there is this value "Tolerance" .. what does that mean?
variation in actual value v. nominal value for individual devices from a batch - for your application
it doesn't matter, what matters more is track linearity, and that might not be crucial either.
Quote
3) how are those one named, thich pins are bend 90° ? (example)
board-mount, PCB-mount, PCB
Quote
4) I saw there are potentiometers with different pin length.. is it just to fit the caps, or are there other defferences I should know?
You mean shaft length?  Because one size does not fit all.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

DVDdoug

#2
Dec 14, 2016, 05:06 pm Last Edit: Dec 14, 2016, 05:09 pm by DVDdoug
Quote
the potentiometers I used are 10K .. but there are also ones with other resistance..
can I use them all?
what do I have to consider if I take a other potentiometer with a other resistance-value?
It depends on the application. 

In the Analog Read Serial example the resistance isn't critical because you are making a voltage divider.    A 10K pot set to the middle* is a 5K-5K voltage divider and you'll get half the voltage.  A 20K pot set to the middle is a 10K-10K voltage divider and you still get half the voltage.

The Arduino's inputs have "almost infinite" resistance/impedance so it doesn't affect the voltage divider.    In other circuits, you may not be so lucky and the pot/voltage divider resistance may be more critical.

Or, if you are using a pot as a volume control on the input of the amplifier, it can affect the input impedance.

Quote
2) there is this value "Tolerance" .. what does that mean?
Nothing is perfect in the "analog world".   If you buy a gallon of milk, one gallon may have one drop more or one drop less than a gallon.   (I don't know what the tolerance is, but the government might require that there is at least  one gallon.   On the other hand, eggs are digital - If you buy one dozen eggs there are exactly 12 eggs in the carton.

If you buy a 1K / 10% resistor, the value can be between 900 and 1100 Ohms.  5% and 1% resistors are super-common.   You can buy 0.1% and 0.01% resistors but they get expensive.

You multimeter also has tolerances.   A good meter will typically be within 1% and the accuracy of a good meter will be spelled-out in the user manual.   (With a cheap meter you might not know.)    And if you work at an electronics company, the meters (and all measurement equipment) are usually sent-out for calibration periodically to make sure it stays in-spec.   


* There is another spec for pots called linearity.   A perfectly-linear pot set to the middle would be 50/50, but again nothing's perfect and there are tolerances.   

Note that audio taper pots (for volume controls) are not linear, they are approximately logarithmic because our hearing (and our perception in general) is approximately logarithmic (or proportional).   

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