Trouble understanding pots/voltage dividers... - diyAudio
Go Back   Home > Forums > General Interest > Everything Else

Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 18th April 2012, 01:02 AM   #1
diyAudio Member
 
Join Date: Apr 2012
Question Trouble understanding pots/voltage dividers...

In the past month or two I've been teaching myself about electronics from the ground up with various textbooks (mainly Grob's Basic Electronics). But I'm stumped when it comes to potentiometers/voltage dividers. The concept of reducing voltage, especially through resistors, doesn't make any sense to me. I was under the impression that resistance only affects current, not voltage. But apparently pots are the exception to this rule... I just don't understand why.

Help!
  Reply With Quote
Old 18th April 2012, 01:15 AM   #2
Butcher is offline Butcher  New Zealand
diyAudio Member
 
Butcher's Avatar
 
Join Date: Oct 2011
Look at it as water. Good analogy maybe ?
  Reply With Quote
Old 18th April 2012, 01:22 AM   #3
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by aBarrett View Post
In the past month or two I've been teaching myself about electronics from the ground up with various textbooks (mainly Grob's Basic Electronics). But I'm stumped when it comes to potentiometers/voltage dividers. The concept of reducing voltage, especially through resistors, doesn't make any sense to me. I was under the impression that resistance only affects current, not voltage. But apparently pots are the exception to this rule... I just don't understand why.

Help!
If you have a resistance and the current changes then the voltage must change too. Its just ohms law.
  Reply With Quote
Old 18th April 2012, 01:37 AM   #4
diyAudio Member
 
Join Date: Apr 2012
Quote:
Originally Posted by nigelwright7557 View Post
If you have a resistance and the current changes then the voltage must change too. Its just ohms law.
I understand the mathematics, but the actual process makes no real sense to me. I can predict what a potentiometer will do in a circuit, but no idea how it does it. How in the world is voltage variated?
  Reply With Quote
Old 18th April 2012, 02:42 AM   #5
diyAudio Member
 
sofaspud's Avatar
 
Join Date: Nov 2005
Location: San Antonio
The wiper of the potentiometer can be set anywhere along its length. The entire voltage is across the potentiometer, so the wiper can be set to tap off a particular voltage.
Maybe imagining the potentiometer as two separate resistors, and the comparative values can be adjusted, with the wiper connecting to the node between the resistors. If the resistor values are equal, the voltage at the node is V/2; if the upper resistor is twice the value of the lower one the voltage at the node is V/3. If the upper resistor is half that of the lower the voltage is V/0.67. The voltage isn't "variated," only the point referenced by the wiper is changed.
With a rheostat, the current is actually changed.
__________________
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
  Reply With Quote
Old 18th April 2012, 03:02 AM   #6
diyAudio Member
 
Join Date: Apr 2012
Aha! I was listening to Yes while drawing some diagrams off the top of my head, and suddenly it hit me like a rock. A potentiometer is a gate for a separate pathway. The "main" pathway is independent of the alternate pot pathway, but the pot pathway is dependent on the main pathway's current.

If a primary voltage source is providing 100V, and there's a pot with a resistance of 10 ohms, the current is therefore 10 amps. When the wiper is placed directly in the middle of the resistor, it creates a potential difference of 50V between pot's first and second terminal, because the current stays the same!

After really thinking about it and actually working with it on paper, it's fairly obvious. The current can't change in this context, and there's a variable amount of resistance. The voltage of the electrical source is irrelevant, which is what I was having trouble grasping.
  Reply With Quote
Old 18th April 2012, 03:24 AM   #7
Butcher is offline Butcher  New Zealand
diyAudio Member
 
Butcher's Avatar
 
Join Date: Oct 2011
If you got 0V on one side, and say 10V on the other, the wiper of the pot can output between 0V and 10V. 0V = 0 and 10V is maximum potential. It is a way of adjusting VOLTAGE between 0V and 10V. The output current is limited by the resistance.

Hope this helps Mr. Barrett?

Tony.
  Reply With Quote
Old 18th April 2012, 03:25 AM   #8
Butcher is offline Butcher  New Zealand
diyAudio Member
 
Butcher's Avatar
 
Join Date: Oct 2011
ps. Research "potential divider"

Tony.
  Reply With Quote
Old 18th April 2012, 10:50 AM   #9
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
I think your confusion arose because you only thought of a resistor as something which when given a voltage creates a current. A resistor is also something which when given a current creates a voltage. These two views, both of which must be kept in mind, are actually the two opposite ends of a complete continuum.

When two resistors are in series (as in a potential divider) then neither of them is at the end of the continuum. They each help set the voltage and current for the other one. The net result has to be what Ohm's Law tells us.
  Reply With Quote
Old 18th April 2012, 11:01 AM   #10
Enzo is offline Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
I have been in this close to 60 years, and I have not yet seen Ohm's Law violated.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Digital pots, better or worse than analogue pots ? nigelwright7557 Parts 8 25th October 2011 05:10 PM
DAC clock frequency dividers 3nity Digital Line Level 19 14th May 2011 12:54 AM
Sliding Pots vs Circular Pots for an equalizer inverseopamp Digital Line Level 13 27th April 2011 07:31 PM
need help understanding voltage regulator schematic (using CCS) from Raleigh Audio jarthel Tubes / Valves 21 29th September 2006 11:08 AM
Help Understanding CD Player Output Voltage, etc. Stew Digital Source 5 26th February 2006 02:39 PM


New To Site? Need Help?

All times are GMT. The time now is 04:28 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2