[SOLVED] Trimmer potentiometers: how to use and choose

[LandLack]

Hi all,
as always, I need some help with some information about trimmer potentiometers:
1-I don't know why there are three pins; shouldn't it have the need of only two since it's a resistance?
2-Also, I don't know why the resistance is said to be one certain value (i.e.50Kohm), while on the datasheets it says different range of values (i.e from 10ohm to 10Mohm). I thought that the first impedance value was the maximum, at first.

In general I need a voltage divider, so I want to use a fixed resistor and a variable resistor. I've been said that the trimmer potentiometers are the variable resistors I needed. I've tried to read infos on the net, but these don't respond to my two questions.

Regards,
LandLack

 

[pinout]

To help with your understanding, consider a lenght or resistance wire which is say 100ohms per metre.
The resistance, end to end for a 1m length will be 100 ohms however if you measure anywhere along its length, the resistance from the end will be proportional to the distance being measured. Note that the end to end resistance hasn't changed.

Now the contact you made along the length is equivalent to the variable resistor wiper, hence our three terminals;the two ends and the wiper.

The potentiometer resistance is the end to end resistance and you can obviously select any resistance up to that between the one end terminal and the wiper. But due to construction of the potentiometer there is a minimum resistance limit.

For a voltage divider you van apply the voltage across the two end resistance terminals and then take off the divided down value at the wiper.
If your variable voltage range is much less than the supplied voltage you can make the potentiometer more responsive (easier to set) by adding fixed resistors at the supply end and/or the low voltage end to get say 2 to 3 V range from a 5V supply.

 

[FvM]

1. Please review the first paragraph of this article for an explanation of the purpose of the three potentiometer terminals. In fact it's a voltage divider in one part. https://en.wikipedia.org/wiki/Potentiometer

A potentiometer, informally a pot, is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat.

2. Potentiometers are made with different resistance values. You'll have to choose a value that fits best your application, but the datasheet describes all available types.

 

[LandLack]

Ok, thank you very much; so I can now connect the device on the wiper pad, while the two main terminals are connected to the voltage supply and ground, right?
Also, I can use the particular device nominal resistance value as the reference, and not the range of values in the datasheet since it's referred to the family of the product, correct?
Thank you again for your help, and have a nice day.

Regards,
LandLack

 

[FvM]

Yes, that's sounds promising.