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Re: How do I get rid of noise spikes on my Power lines

From: Sandor Ajzenstat   sandorinterlog.com
Date: Mon, 16 Aug 2004 11:02:29 -0700

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Dear Jessica,

I have had great luck in eliminating spikes using 1uF nonpolar capacitors.
Everything I'm describing here is related to things I needed to do for one
piece in order to get rid of intermittent spikes.  I would suggest picking
up 10 or 15 of these 1uF nonpolar caps, as well as an assortment of smaller
value nonpolar caps, and experimenting with them in various places.

Step one.  I would certainly suggest placing one across the power lines that
feed the fan  I would start by placing the cap as close as I can to the
actual fan inputs..  Also, I would place one across the DC power lines
wherever they enter any circuit board after running along a cable.
Experiment with them in other places too.

Step two would be to ensure that for long cable runs that your wire gauge is
sufficient.  Believe it or not I have found that to run 5 volts DC along say
20 feet or so I really need to use at least 18 (or prefferably 16) gauge
wire.  Otherwise the resistance which accumulates along the length of the
conductor can weaken signal strength too much in relation to spike strenght.
If you don't think wire gauge is an issue then skip this step and possibly
return to it later if necessary.

Step three.  After having done the above, I still had intermittent spike
problems, although they now occurred at different times.  I found that
placing a 1uF nonpolar cap across from Signal to GND where those wires
entered a circuit board, completely cleaned up absolutely every spike.
Unfortunately it also cleaned up all my data pulses too.  In order to get
around this I substantially lengthened the duty cycle for all my data pulses
until they were of a long enough duration to get past the cap.  To do this I
just used a whole bunch of NOP instructions.  This may not apply in your
case because all your signals may travel via wireless, and not via copper
conductor.  Mind you, on a given circuit board spikes may be entering your
signal lines, so it's worth thinking about. If your existing spike durations
are very short in relation to your data transition durations then it ought
to be possible to find the right value of cap to clean up spikes without
affecting the data transitions. This would take time and experimentation.

Step four.  When you're next at Supremetronics, use diagrams to precisely
describe your problem to Kirk.  He's one of the younger guys behind the
counter there.  Kirk may be able to make recommendations or suggestions.

Do not worry.  There is a solution.  The way to find it is by patiently and
systematically trying things, and by keeping track of your progress in note
form as you go.

Generally, as I have done tests with various caps, I have left in place the
ones I've already positioned, while adding other ones in other places.  A
complete solution may require numerous caps strategically placed in a
project.

Good luck, but you won't need it.  You'll work it all out.
Sandor




----- Original Message -----
From: "jessica field" 
To: <arg-list@xxxxxxxxxxxxxxx>
Sent: Monday, August 16, 2004 6:20 AM
Subject: ARG: How do I get rid of noise spikes on my Power lines


> A! Sent via the Art & Robotics Group mailing list:
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> I am using a PC power supply to power my electronic application.  If I use
the +5 V output that does not run when the Power supply's fan is on, my
wireless network works perfectly.  As soon as I turn on the other voltages
and the fan in the power supply, I get noise spikes on my +5 V supply and I
have no wireless communication.  I need +12 V to run other periferials so I
need to have my wireless working when the PC power supply's fan is on.  I
have designed my casing to have the PC power supply so I would very much
like to use it so I don't have to redesign everything.  I am on a tight time
crunch to finish my project.
>
> I was wondering if anyone knew some good solutions.  I have used a 220 nf
capacitor on the positive and negative line to try to clean up the noise.
It helps a bit but I still need a better filtering system.  My electronics
are on more than one board and my wireless transiever is relatively far from
power supply and the Main board in wiring.
>
> Any help would be very appreciated.
>
> Jessica
>
>
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