Common beginner mistake, you're seeing the difference in grounds between
teh scope and your board.  What you need to do is ground the scope probe
to your project ground.  There are usually ground clips that attach to the
probe and can clamp onto a ground on the board you're testing.  Need to be
CAREFUL especially if your project is not battery powered, though.  8)

Now I'm sure half a dozen people with more knowledge of how scope grounds
are isolated will jump in with more detail...

Dale
--
"Curiosity is the very basis of education and if you tell me that
curiosity killed the cat, I say only the cat died nobly."
          - Arnold Edinborough


On Wed, 13 Feb 2002, Rodrigo Valladares P. wrote:

> Hi all,
>
> After reading the benefit of an oscilloscope, i took one that is not used in
> my work to debug (is this used in hardware too ?) a pic circuit. I have ZERO
> experience with scopes, so, and i attach the probe to Ch1, the probe has a
> clip, i grip it to gnd and the pin of the probe to what was i really want to
> measure... BUT, i have a 50Hz superimposed over my signal, and showme not
> really what i expect, then measuring the line ac make some spark in the
> probe (the scope can accept 400 vac). Using a tester, and the scope off, i
> discover that the clip is connected to the line ground (0 ohm), and i
> suppose that the test probe was isolated from the main line. I'm wrong and i
> must go to buy "measuring with a scope for newbies" or the scope is bad?, i
> don't have none to ask in my work, because is not used and is there only by
> a mistake
>
> The scope is a tektronix tds-310, and the probes (both with the same result)
> P6109B 10X
>
> ( BTW, 50 Hz is the line frequency here )
>
> Thanks in advance
>
> RVP.
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>
>

--
http://www.piclist.com hint: The PICList is archived three different
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