Current Sensing Resistor


Closed Thread
Results 1 to 4 of 4
  1. #1
    Join Date
    Jan 2007
    Posts
    44

    Default Current Sensing Resistor

    Hi. I want to make a current sensing device, and I read somewhere (cant remember now) that you could you a small value resistor (about 0.1R) a measure the current drop across it. But how do I calculate the current from that value??? Should I use a simple op amp to amplify the voltage drop (like the 741)???
    Thanks!!! Manuel
    Last edited by manumenzella; - 17th February 2007 at 08:12.

  2. #2
    Join Date
    Oct 2005
    Location
    Loveland CO USA
    Posts
    83


    Did you find this post helpful? Yes | No

    Default current

    Manuel,

    1 ohm=1 volt for 1 amp. 1 ohm=2 volts for 2 amps.
    0.1 ohm=0.1 volt for 1 amp.
    I think you can do the math.
    Question AC or DC. This may make a difference. How much current? Power Line? (110/220)?
    What resolution? If you want to know; is load on (about 0.1 volts) or is load off (about 0 volts) then the PIC can measure directly with no amplifier. If you want to know 1.05 amps then you will need a amplifier! (0 to 0.1 volts on resistor---50x amplifier---0 to 5 volts to PIC.

    rons

  3. #3
    Join Date
    Feb 2005
    Location
    Kolkata-India
    Posts
    563


    Did you find this post helpful? Yes | No

    Default You can use LM358 too

    Hi,

    It is important whether you are doing a high side or low side sensing. Low side is the easiest and most frequently used. LM358 is a dual supply amp and works with a single 5 volt supply. Please note that it is not rail-to-rail. That means your op-amp cannot output the entire supply voltage range. If you a using a dual supply then you can use OP07 and pin to pin replacement for LM741 but with better offset voltage characteristic.

    Please describe your exact requirements so that some possible schematics can be posted.
    Regards

    Sougata

  4. #4
    Join Date
    Jan 2007
    Posts
    44


    Did you find this post helpful? Yes | No

    Default

    Hey. Thanks for your answers. I would like to make a battery dircharger / analizer, so the resolution will have to be quite good. The discharge rate will be about 200 - 400 mah. Can you send me any example of using an op-amp to amplify the voltage. Thanks agaaaaaaaaaaaain!!!!!
    Manuel

Similar Threads

  1. Can I drive a 5v LED without a current resistor?
    By Fredrick in forum Schematics
    Replies: 31
    Last Post: - 11th September 2009, 15:42
  2. Replies: 8
    Last Post: - 5th May 2009, 21:10
  3. Calulating BJT base resistance for PIC led switching?
    By xnihilo in forum mel PIC BASIC Pro
    Replies: 11
    Last Post: - 20th November 2008, 09:41
  4. 16F628A current high during sleep
    By Rubicon in forum mel PIC BASIC Pro
    Replies: 5
    Last Post: - 9th October 2006, 11:21
  5. Do I need that Resistor with my LCD?
    By Melanie in forum FAQ - Frequently Asked Questions
    Replies: 0
    Last Post: - 15th July 2004, 11:50

Members who have read this thread : 1

You do not have permission to view the list of names.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts