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Powering a 5V and a 9V circuit from one 9V battery -- isolation help?

Discussion in 'Electronic Design' started by [email protected], Jul 2, 2006.

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  1. Guest

    For size/weight reasons, I'm hoping to use a single 9V battery plus
    mic2950 5V regulator to power a mini video camera (9V) and some RC
    servos (5V). Unfortunately, every time the servos move, there's a burst
    of interference on the video signal. There's no interference when the
    camera and the servos are powered by separate batteries.
    The circuit is simple: 9V battery, mic2950, camera, and RC stuff, just
    wired together the obvious way. I tried adding a capacitor between
    output and ground of the regulator, but that didn't have any effect.
    Is there any way to eliminate the interference?
    Or, is there a 5 or 6V power source that's smaller than 4AA cells, or
    an alternate 9V battery that's smaller than the usual?
    Thanks for your attention.


    Michael
     
  2. Phil Allison

    Phil Allison Guest

    ** Hotmail & GG !

    Double whammy .....

    ** What sort of servos draw under 150mA ?

    The servo load current is hammering the battery and causing the noise.

    Using the 5 volt reg has no effect on this.


    ** Yeah - use as decent 9 volt battery and a decent reg IC.


    ** Yep, 4 or 5 AAA cells, Ni-Cd or NiMH

    The very low internal resistance will make a BIG improvement.



    ....... Phil
     
  3. Guest

    It's tried-and-true solution to have separate power supplies for the
    motors and the control circuitry. Your system has already demonstrated
    that it works well this way, so if you go with the flow, you can
    optimize the batteries for each subsystem. Your control circuit and
    video might be able to get by with a couple of lightweight lithium
    cells @ 3 volts each. Meanwhile, your servo motors could run on some
    sort of rechargeable cells because that's where the bulk of your power
    is being consumed. This also allows you to maintain full control and
    video even when the servo motor batteries are getting low.
     
  4. Luhan

    Luhan Guest

    I've done this before without any problems. The camera was 12 volts
    and the servos were powered from a 7805 regulator with about 100uf on
    both the input and output. You dont need a fancy low-dropout regulator
    for this application.

    Also, watch out for any common ground connections, run both bach to the
    battery seperately. Or, try physically moving the servos away from the
    camera to see if the coupling is inductive from the motor coils.

    Good luck,
    Luhan
     
  5. Guest

    Thanks all for the rapid and helpful responses! On a Sunday morning, no
    less.
     
  6. Guest

    Hmmm. Is there something I can add to become a triple threat?
     
  7. James Waldby

    James Waldby Guest

    Sure,
    3. Top-post,
    4. Add a big ascii-graphics sig,
    5. Don't quote the posts you reply to,
    6. Use 733t spelling (l33t speak),
    7. Tell the old guard they're newbies,
    etc, etc.
    -jiw
     
  8. Guest

    Thanks!
     
  9. Rich Grise

    Rich Grise Guest

    Yeah - keep feeding the troll. ;-)

    Good Luck!
    Rich
     
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