Author Topic: Variable resistors and loss of wiper contact  (Read 1009 times)

0 Members and 1 Guest are viewing this topic.

Offline ifonlyeverythingTopic starter

  • Regular Contributor
  • *
  • Posts: 146
  • Country: us
Variable resistors and loss of wiper contact
« on: October 08, 2024, 05:55:19 pm »
I feel dumb for asking this, but I need to take a 12V input and divide it down to 0-5V. I know that it's best practice to tie the wiper to one of the other legs to protect against the wiper losing contact -- which would be bad. So something like this appears to work in that regard. However, as I have the schematic drawn, if the wiper loses contact then the resistor maxes out at 10K and the output voltage goes to 5V. Is there a way to do this so loss of contact instead outputs 0V?



 

Offline Kim Christensen

  • Super Contributor
  • ***
  • Posts: 1819
  • Country: ca
Re: Variable resistors and loss of wiper contact
« Reply #1 on: October 08, 2024, 07:02:36 pm »
Loss of wiper contact with this circuit would result in 0V at the voltmeter:
EDIT: Or do you want two POTs? (Trimmer and regular)
« Last Edit: October 08, 2024, 07:06:29 pm by Kim Christensen »
 
The following users thanked this post: ifonlyeverything

Offline PGPG

  • Frequent Contributor
  • **
  • Posts: 972
  • Country: pl
Re: Variable resistors and loss of wiper contact
« Reply #2 on: October 08, 2024, 07:12:35 pm »
You can do the divider with 14k resistor and 10k variable resistor and take output from viper.
 

Online Gyro

  • Super Contributor
  • ***
  • Posts: 10790
  • Country: gb
Re: Variable resistors and loss of wiper contact
« Reply #3 on: October 08, 2024, 07:27:11 pm »
A lesson from Metrology... For voltage dividers, put the variable resistor in parallel with one of the fixed resistors. Calculate the resistor values so that the variable resistor adjustment range is only sufficient to compensate for worst case resistor and other tolerances. That way, if the wiper goes open circuit, nothing dramatic will happen. Always start with two fixed resistors for the divider and provide the minimum adjustment needed.
Best Regards, Chris
 

Offline ifonlyeverythingTopic starter

  • Regular Contributor
  • *
  • Posts: 146
  • Country: us
Re: Variable resistors and loss of wiper contact
« Reply #4 on: October 08, 2024, 10:26:35 pm »
Loss of wiper contact with this circuit would result in 0V at the voltmeter:
EDIT: Or do you want two POTs? (Trimmer and regular)

I did want a trimmer and a regulator potentiometer but I figured it out from your schematic. Thank you, I don't know why I didn't think of this!
 

Offline Doctorandus_P

  • Super Contributor
  • ***
  • Posts: 4703
  • Country: nl
Re: Variable resistors and loss of wiper contact
« Reply #5 on: October 08, 2024, 11:00:50 pm »
Another method is to put the ends of the potentiometer to GND and 12V and the wiper to 5V.
And of course add resistors to the end to limit the adjustment range and add precision.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf