> Hi !
> I'd like to use my Pc's parallel port for i/o. I know how to handle
> this, except for a little problem : I don't want to connect an
> extension directly to my PC, so I'd like to use an (fr.)
> "optocoupleur" (a generally 6-pinnel DIL IC composed of a LED and a
> phototransistor, you see what I mean ?).
> I know this is used on lots of cards, but I read that CMOS ans more
> particulary TTL outputs can't properly drive a LED, because of its
> limited output current (2 mA, which I measured on my port). A solution
> is given, using +vcc and the output as a ground, but I can't use it
> (no vcc output on // port !).
> So what ? Does one use special "optocoupleurs", with a limited input
> current (which I suppose are more expensive), or is there a way I can
> use more "classical" optos ?
> Thanks !
with this is that it has no voltage isolation. Motors can generate
considerable counter EMF that will intern generate large voltages. The
best bet is to use optoisolators. These have the voltage isolation the
additional card doesn't.