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PICList Thread
'RF interference'
1996\11\05@194947 by TONY NIXON 54964

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Has any one got any ideas to stop RF from causing false readings
on an input.

Tony


Just when I thought I knew it all,
I learned that I didn't.

1996\11\05@203355 by peter

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TONY NIXON 54964 wrote:
>
> Has any one got any ideas to stop RF from causing false readings
> on an input.
>
> Tony
>
> Just when I thought I knew it all,
> I learned that I didn't.

first a resistor(try 100 to 1k ) then pass it through a 1nf feedthrough
cap
In extreme cases you can do this more than once
--
Peter Cousens
email: spam_OUTpeterTakeThisOuTspamcousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,

1996\11\05@210814 by Martin J. Maney

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On Wed, 6 Nov 1996, TONY NIXON 54964 wrote:

> Has any one got any ideas to stop RF from causing false readings
> on an input.

Well, filter it out of course.  If the measuring system isn't already
shielded, start with that.  If that doesn't work you can try input
filtering.  Sometimes a simple capacitor bypass will suffice, but there's
no set rule.  And of course you could find that the interference isn't
actually entering on the input leads, but rather on an output or supply
and getting coupled to the circuit.

Luck!

1996\11\06@163513 by Bradley, Larry

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As suggested by others, a simple capacitor might help. Depends on the
frequency of the RF.
You can get small ferrite beads that can be slipped over wire leads to
filter out RF. Putting the PIC and assoc. circuitry in a metal box, and
using feed-through capacitors (and possible ferrite beads as well) on
ALL leads going into the box is perhaps overkill, but will certainly
work.

Larry

{Quote hidden}

1996\11\07@132510 by Reginald Neale

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Another thing that can help is to keep all circuit impedances as low as
possible. Any inputs that are not driven should be pulled to one rail or
the other with the lowest practicable resistance.

.....................Reg Neale.....................
Complete text of the winning entry in a recent good-government essay contest:
"Good Government.  Gooooood Government.   Sit.    Stay."

1996\11\10@210211 by Len Umina

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Hi,

An RF bypass cap to ground should do it.  Try .001 uF to ground as near to
the input as possible.  If you are in a really bad environment you might
need to make sure your ground is really a ground as RF can bias your supply
rails, particularly if the leads to and from the supply are "resonent"
which essentially means they are 1/4 wave long at the frequency of interest
(or an multiple thereof)

If you find such a situation, I would recommend RF chokes in the ground and
supply leads.  The inductance is a function of frequency.  A small toroid
can be effective, as can be the split cores that wrap around wires.  A
bypass cap having good RF performance of .01 where the leads enter the
board is also important.en

73,
Len WA1IOB

/96 GMT+1100, you wrote:
>Has any one got any ideas to stop RF from causing false readings
>on an input.
>
>Tony
>
>
>Just when I thought I knew it all,
>I learned that I didn't.
>
>

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