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

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.


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** 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

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Phil Allison

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.

-- Joe Legris

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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

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

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

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


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James Waldby

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Yeah - keep feeding the troll. ;-)

Good Luck! Rich

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Rich Grise

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