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, b=
ut also tied a LED to the same signal.

Thought of course is....opto comes on, drives the collector low, turns on t=
he LED and PIC sees it.=A0=A0 Well the LED does turn on, but the PIC wasnt =
seeing it low.=A0 Looking just with a voltmeter, its sitting about 2.4V, so=
 its still a high.=A0 OK, physics still work.

I changed out the resistor driving the opto's LED from a 2K to a 1K, thinki=
ng that driving the LED harder will turn on the transistor harder...if it w=
asn't fully saturated then its possible it can't drive all the way low.=A0 =
No change.=A0 Did a really quick LTspice, and it simulates the way I expect=
....goes to ground.=A0=20


But now I'm thinking we might have a voltage divider between the pup and th=
e LED circuit?=A0 The other solution, that Ive done before and probably sho=
uld have on this was to put the LED in series with the opto input.=A0=A0 si=
gnal..resistor....LED.....opto's LED....ground.

Just wondering what I can do with the existing circuit


--=20
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