Utility of 0,1µF capa when batteries are used


Closed Thread
Results 1 to 6 of 6
  1. #1
    Join Date
    Aug 2006
    Location
    SWITZERLAND (french speaking)
    Posts
    938

    Default Utility of 0,1µF capa when batteries are used

    Hello,

    It is well known: always connect a 0,1µF between VDD and GND on a PIC!

    I'm curious to know if this is still needed when the kit is powered with batteries?

    If yes, what would be the reason?
    Roger

  2. #2
    Join Date
    May 2004
    Location
    NW France
    Posts
    3,648


    Did you find this post helpful? Yes | No

    Talking

    Hi, Roger

    Why do you always want to rebuild the world ???

    Just take a scoping of the supply lines on the PIC pins ... and watch the difference ...

    In certain configs no cap doesn't really matter ... in others you can't do anyting with your PIC. Batteries or not batteries.

    ( I MEASURED a half full 4 Sanyo 2100 mAh NiMh AA cells batt @ 0.45 Ohm internal resistance ... 78L05 does much better !!! )

    If you need ONE good reason ... consider RFI generating on supply lines AND RF Generation.

    Alain
    Last edited by Acetronics2; - 26th April 2009 at 13:22.
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  3. #3
    Join Date
    Nov 2005
    Posts
    51


    Did you find this post helpful? Yes | No

    Default

    Yes they still would be needed, The reason they are needed is they are known has decoupling capaictors, Thelp help prevent noise which could effect the pic or any other part of your curcuit it aslo helps out with the EMC rules, The normal rule every IC is best to have a 100N(.1uF) cap has close has possible to the IC power pins.

    There may be more reason but these are the simples ones

  4. #4
    Join Date
    Aug 2006
    Location
    SWITZERLAND (french speaking)
    Posts
    938


    Did you find this post helpful? Yes | No

    Default

    Okay, okay guys, I was just asking...

    Gonna have a look at this with a scope.

    Is this capacitor that usefull, it should be embeded in the PIC, no?

    Thanks a lot for your remarks and interresting infos.
    Last edited by flotulopex; - 26th April 2009 at 18:49. Reason: Adds
    Roger

  5. #5
    Join Date
    Nov 2003
    Location
    Greece
    Posts
    4,115


    Did you find this post helpful? Yes | No

    Default

    Every switching circuit needs the caps.

    Think of the internal circuits of the output pin either PIC or a TTL circuit. It conducts Vcc to the output then this transistor is put in off state and the other to the ground is switched on.

    In an ideal world this is what should happen. But the world is not as ideal as we wish to be, so there is a small fraction of time where these two little transistors conduct at the same time producing a power drop.

    You can see this in the scope clearly. Put the capacitor and all will be much cleaner. Power source has little to do with this, batteries being better in that they do not try to correct the drop by raising the level and then producing overshot.

    Hope is more clear now.

    So, bottom line:

    Whatever you do use always capacitors!

    Ioannis

  6. #6
    Join Date
    Aug 2006
    Location
    SWITZERLAND (french speaking)
    Posts
    938


    Did you find this post helpful? Yes | No

    Thumbs up All Clear

    Thank you again for being that clear.
    Roger

Members who have read this thread : 0

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