Help: how to wire a potentiometer ?

[Chris Riddell]

Hello,

I have just started out in electronics and am having a current problem with a little simple project I'm making right now. The problem I'm having is with a 1M Pot, I've never made a circuit yet with one of these and need some advice.

I'm making this following circuit, and have two of the following 1m Pots to use (see bottom of image) now what pins on the pots do I need to connect to the parts on the circuit I have marked with question marks?

Any help would be great and sorry if this is super basic :-\

 

[KrisBlueNZ]

Hi Chris and welcome to Electronics Point

That's a fair question. Potentiometers and preset potentiometers (trimpots) have a resistive track with two end terminals, and a wiper that moves along the track. This is clear from the trimpot in the right of your photo, where the wiper corresponds to the blue dot. The potentiometer on the left is the same, with the wiper connectd to the middle terminal, i.e. the green dot.

The resistance between the two end terminals doesn't change, so to use a potentiometer as a "variable resistor", i.e. a two-terminal device whose resistance is adjustable (also called a rheostat), you need to use the wiper and one of the end terminals.

Which end terminal do you use? It depends whether you want the resistance to increase or decrease as you rotate it in a given direction.

For example, if the pot/trimpot adjusts a delay, you would normally want clockwise rotation to increase the delay, which means it needs to increase the resistance, because in a timing circuit made with a resistance and a capacitor, the time is proportional to R × C so a higher resistance causes a longer delay. In this case you need to connect to the anticlockwise end of the track (in your photo, the red dot on the pot and on the trimpot) and the wiper, so when the pot is fully anticlockwise the resistance is zero and resistance increases as you turn it clockwise.

If the pot/trimpot adjusts a frequency, you would normally wnat clockwise rotation to increase the frequency, which means it needs to decrease the resistance, because in an oscillator made with a resistance and a capacitor, frequency is proportional to 1 / (R × C), i.e. proportional to the reciprocal of resistance, so a lower resistance caues a higher frequency. In this case you need to connect to the clockwise end of the track (in your photo, the blue dot on the pot, or the green dot on the trimpot) and the wiper, so when the pot is fully anticlockwise the resistance is maximum and resistance decreases as you turn it clockwise.

That covers the cases where a pot/trimpot controls a time delay and a frequency, which are pretty common. There are other cases, and you need to know how the circuit responds to the resistance to be able to work out which end to connect to. The "law" of the pot can also be involved - whether it's a linear pot, a logarithmic pot, or something else. But that's another subject

 

[Chris Riddell]

Thank you very much Kris

So I understand now for this circuit I will always need the wiper part connected (Green in the big pot) and (Blue on the little pot) and then have one of the terminals connected depending on what direction I wish the switch to operate. saying that what do I need to connect to X and what to Y? I.E. Where on this circuit would the wiper be connected to?

Cheers

 

[BobK]

When using only 2 terminals from the POT, it does not matter which is connected to which point in the circuit. Just like it does not matter which lead from a resistor is connected to which point in the circuit.

Bob

 

[Chris Riddell]

Thanks guys most helpful and it now works I'm glad I joined this forum...

 

[dwn]

Kris, thanks for that clear and straightforward answer to potentiometers. Personally, I start to get a little lost in the technical jargon and the internet can have too many resources. Your explanation really helped to clarify the pots for me.