Don't forget about the Current Transfer Ratio (CTR) for the opto coupler. I=
f it=20
isn't a darlington opto this is likely less than 100%. Try to use a draling=
ton=20
opto instead.

Also make sure that the PIC pin really is an input. I would imagine that th=
is=20
could happen if the PIC pin is set to an output that is driven high.

/Ruben


> I have a 12V signal coming into a board, so I'm using an opto to isolate =
it
> (comes from a longish cable), so tied a 10K pup to 5V, and into the PIC, =
but
> also tied a LED to the same signal.
>=20
> Thought of course is....opto comes on, drives the collector low, turns on=
 the
> LED and PIC sees it.=A0=A0 Well the LED does turn on, but the PIC wasnt s=
eeing it
> low.=A0 Looking just with a voltmeter, its sitting about 2.4V, so its sti=
ll a
> high.=A0 OK, physics still work.
>=20
> I changed out the resistor driving the opto's LED from a 2K to a 1K, thin=
king
> that driving the LED harder will turn on the transistor harder...if it wa=
sn't
> fully saturated then its possible it can't drive all the way low.=A0 No c=
hange.=A0
> Did a really quick LTspice, and it simulates the way I expect...goes to g=
round.=A0
>=20
>=20
>=20
> But now I'm thinking we might have a voltage divider between the pup and =
the LED
> circuit?=A0 The other solution, that Ive done before and probably should =
have on
> this was to put the LED in series with the opto input.=A0=A0
> signal..resistor....LED.....opto's LED....ground.
>=20
> Just wondering what I can do with the existing circuit
>=20
>=20
> --=20
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>=20
>=20
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>=20
>=20

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D

--=20
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.