Hello,
I am using small carbon trim pots as variable resistors.
In my schematics I am using only the wiper and a second pin. The third pin is left unconnected. Is there any reason to connect a pin directly to the wiper instead ?
Thank you in advance.
amundsen:
Hello,I am using small carbon trim pots as variable resistors.
In my schematics I am using only the wiper and a second pin. The third pin is left unconnected. Is there any reason to connect a pin directly to the wiper instead ?
Thank you in advance.
It depends if you want the potentiometer to act like a potentiometer or a rheostat. There is a difference and without showing how you are using your pot in a complete circuit the only answer possible is, maybe, maybe not.
Lefty
Yes, connect the wiper to one end, then if the contact is a bit scratchy you'll prevent
the resistance rising above the total of the pot's track (reduces the max noise spikes
when the contact is scratchy/dirty). For log pots you want to connect the wiper to
the correct end, note, to retain logarithmic response.
retrolefty:
It depends if you want the potentiometer to act like a potentiometer or a rheostat. There is a difference and without showing how you are using your pot in a complete circuit the only answer possible is, maybe, maybe not.
Actually the idea is to use small trimpots to set precise resistance values. The trimmers will be set once only.
amundsen:
retrolefty:
It depends if you want the potentiometer to act like a potentiometer or a rheostat. There is a difference and without showing how you are using your pot in a complete circuit the only answer possible is, maybe, maybe not.Actually the idea is to use small trimpots to set precise resistance values. The trimmers will be set once only.
Well trimmers can be set once to a precise value and thus act like an adjustable voltage divider and of course just two terminals can be used to simulate just being an adjustable single resistor.
There have been times where I used a three terminal pot as a 2 terminal resistor and just left one of then end terminals unconnected. However you have to be careful in that because you can adjust the adjustable resistor down to close to zero ohms that there can be serious consequences to the pot or external circuit due to too high a current flow. Often a fixed resistor in series with the adjustable resistance, thus establishing a minimum resistance value, can be used if too low a resistance can have bad effects.
Yes putting a fixed-value resistor in series was my idea too.
Thanks a lot.
You should connect the wiper to one end to prevent noise pickup on the open terminal.
Aaaah voilà !
Thanks Grumpy_Mike !
Grumpy_Mike:
You should connect the wiper to one end to prevent noise pickup on the open terminal.
Well I ain't buying the 'noise pickup' as a problem, but of course that could depend on the circuit impedance the pot is being placed in.
However there is sometimes discontinuity jumps at the two ends of travel for a pot, so wiring the wiper to one end is a good practice, but then again having to adjust a pot to close to either end of travel is an indication of not sizing the pot properly in the first place.
The advice about the end comes from work in the audio field. It stops hum pickup in tone controls.