Circuit for filtering power supply?

Does anyone know any circuits for filtering out noise from your power supply lines? I'm trying to clean up the 12vdc in my robot. It is powering a PC
which introduces noise on the power lines. I hooked up an Oscope and there is a specifc frequency and ripple it introduces. Knowing this, is their a circuit I can use to filter this along with some formulas for figuring out the values of the components?
Thanks!!
-C http://hossweb.com
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Dirty great big capacitor. In parallel.

supply
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Hehe. What do you consider big? I've tried the biggest polorized one I had which was 330uf I beleive, but I dind't see any difference on the scope.
-C http://hossweb.com

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As big as you can get. Try 1000uF, bigger if you can get it. Adding more than one in parallel also and they'll add together.
-Dave
wrote:

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Does it make a difference if the cap is a polorized one or not?
-C http://hossweb.com
"Dave" <blank> wrote:

had
power
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Only if you connect it backwards, in which case it will probably explode.

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No, but polarized capacitors (i.e. aluminum electrolytics) usually have greater capacity for a given size (space they take up).
-Dave
wrote:

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This is a multi-part message in MIME format. --------------73485C40FE1B323CC7B3B3AE Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit
The best circuit for this is probably a pi filter. What sort of noise are you trying to filter out ?
this is made with 2 capacitors and one inductor.
supply + ---------inductor ------------- Output to motor | | | | capacitor capacitor | | ground ground
The Capacitors should be about 1000uf for every 1 amp of motor current drawn. Bigger is usually better. Their rated voltage should be atleast 1.5X your supply voltage. The inductor should have about 50 -500uH of inductance and able to handle the current drawn without getting too hot.
If your microprocessor is glitching or resetting I would recommend using 2 separate filters, one for the motor control and one for the microprocessor.
Check out the ARRL Radio Amateurs Handbook (at your local brick and mortar library ) for an excellent and readable description of practical power supply filters.
Steve
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This is excellent info, thank you very much! I think I will experiemnt with combining this and the suggestion from Zagan (thanks Zagan!). I think these together should be able to at least help clean up my power source. It hasn't really caused me much of a problem yet, but I think I'm getting some slightly erratic readings from my ADC inputs. Everything on my robot is powered off a single large 12v battery. The motors don't seem to inject any noise, its the MiniPC that does it. I can see slight changes in the noise on the Oscope when the harddrive is doing stuff.
Again, Thanks!
-C http://hossweb.com

drawn.
handle the

2
microprocessor.
supply
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C -
Oh dear, did you say the hard drive?
When the drive is being accessed (and depending on the drive vendor, just plain spinning), there could be significant amounts of radiation. It couples into everything through the ether. Caps out the wazoo may not help much. Perhaps you need geometry changes or shielding.
Just a thought, Bill
wrote:

current
using
mortar
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Good point. The PC I'm using is built like a laptop (http://hossweb.com/Robotics/Lazlo%202.0%20-%20Brains.asp ) so the HD is about a milimeter away from the motherboard. Maybe I should move it outside the case and build a small metal box to house it in somewhere away from the robots electronics.
-C http://hossweb.com

help
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supply
[Zagan] Others have suggested large electrolytics, which is a good suggestion for removing ripple, but perhaps what you're seeing on your scope is high frequency digital noise and electrolytics don't work well at such frequencies (for filtering out noise). Try putting a small ceramic (0.1 uF or so) capacitor across the power supply output (or input, or both) and see if that helps. If you still get low frequency ripple, then use an electrolytics as well on the output. The value you need depends on current draw, but 1000 uF or so should work.
// Jim
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