Potentiometers??

[things]

I was going through a few circuit diagrams, and noticed that sometimes the centre contact, and one of the outer contacts were connected directly together. What is this point of this? Would it not just turn the pot into a big resistor??

 

[ericgibbs]

I was going through a few circuit diagrams, and noticed that sometimes the centre contact, and one of the outer contacts were connected directly together. What is this point of this? Would it not just turn the pot into a big resistor??

Its done this way so that the value of the end to end resistance can be changed.

If the centre of the pot isnt tied to one end, the wiper and the two ends of the resistor are a potential divider.

OK.?

 

[Boncuk]

using a trimpot it doesn't make a difference if both outer taps are used or not. The only effective resistance is between one tap and the wiper, e.g. variable feedback resistor.

Using a pot as a voltage divider all three taps must be connected.

 

[3v0]

What Erick said sounds right.

It the terminals are A W B with W the wiper
Lets call the resistance from A to B Rab and
the resistance from A to W Raw

If B and W are connected the resistance
between A and the B W node are.

1/((1/Rab)+(1/Raw))

Edit: connecting the wiper to B shorts out the resistance between W and B so it is as Mr Al said. Opps !

 

[MrAl]

Hello,

Given two ends and one wiper for any 'regular' pot, one end is connected
to the wiper and this makes the pot a variable resistor as the resistance
between the other end and the wiper changes as you turn the shaft.

Of course you can get this action another way...without connected one
end to the wiper. In this way, you can use either end and the wiper for
the variable resistor, and it works the same as above.

So why go through the trouble of connecting one end to the wiper then,
if you can get the same variable resistance without doing that?

The answer is, to lower the noise pickup of the circuit. With one end
completely open it is more susceptible to noise pickup.
This works especially nice if you can ground the end that is connected to
the wiper.

 

[SMUGangsta]

The answer is, to lower the noise pickup of the circuit. With one end
completely open it is more susceptible to noise pickup.
This works especially nice if you can ground the end that is connected to
the wiper.

Never knew that, will be very handy to remember this, as i have wondered about the very same thing.

 

[crutschow]

So why go through the trouble of connecting one end to the wiper then,
if you can get the same variable resistance without doing that?

The answer is, to lower the noise pickup of the circuit. With one end
completely open it is more susceptible to noise pickup.
This works especially nice if you can ground the end that is connected to
the wiper.

Another reason is to avoid a momentary open circuit if the pot wiper momentarily lifts while adjusting the pot. This could be important in certain types of circuits where a momentary open could cause a catastrophic voltage or current somewhere in the circuit.

 

[ericgibbs]

Another reason is to avoid a momentary open circuit if the pot wiper momentarily lifts while adjusting the pot. This could be important in certain types of circuits where a momentary open could cause a catastrophic voltage or current somewhere in the circuit.

hi Carl,
I agree, I never leave one end of a pot disconnected.

 

[SMUGangsta]

Its amazing how much knowledge you can soak up in a few short days, lovin' it

 

[Speakerguy]

Yep, it's bad form to leave a pot terminal disconnected. Always tie the unused terminal to the wiper when using it as a variable resistor.