Re: Optocoulped Parallel port

I have operated optocouplers from a wide variety of notebook and desktop
parallel ports. You definately should not attempt to use the parallel port
as a current source for driving the led's, only as a sink. This inverts the
sense of the output, but you can use an inverter on the isolated side if you
can't adjust for it in software.

Operating as a current sink, I have never seen a parallel port that cannot
driver an opto-isolator led (with a same size over 50).

Dean

<snip>

> > From: stratton@...
> >
> > > You don't use the pullup resistor to power the optocoupler. You use
> >
> > > either the PC
> > > power supply or an external +5V power supply, through a resistor,
> > > through the
> > > LED or optocoupler, and finally to the port output, which will light
> > the
> > > LED when
> > > the output is at logic ZERO, or grounded. More current is available
> >
> > > that way.
> > > This all applies to output from the PC to external devices.
> >