Re: opto isolator and capacitors

Looks good. I laid out my board with 74HCT541 as the isolator for
relays for the output isolation. no isolation for the Geckos' and
only the opto isolator for the inputs.

Trying to keep it simple.

Dave

--- In CAD_CAM_EDM_DRO@y..., "Lee Studley" <indigo_red@q...> wrote:
> Dave,
> Also check out Doug harrison's folder in the files section
> folder name is: "Buffered-Parallel-Port-Intf"
> in particular file: Wb8schem.pdf
>
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/Buffered-
> Parallel-Port-Intf/Wb8schem.pdf
>
> -Lee
>
>
> --- In CAD_CAM_EDM_DRO@y..., "turbulatordude" <davemucha@j...>
wrote:
> > Thank you.
> >
> > I had not used a opto isolator before and it seemed that the
field
> > switch (end switches in my case) just turned on an LED. The LED
> was
> > powered from some external power source. in that manner, only
> light
> > connected the 'protected' PC circuits and if one were to slip and
> > either ground or hit 220 to the LED, all you would loose is the
> > optocoupler. A friend bought a new circular saw some many years
> ago
> > and one if his first project was to saw the cord off. Always
> makes
> > think what if...
> >
> > And I always say that one should learn the mistakes of othes, as
> you
> > will not live long enough to make them all yourself.
> >
> > That being the case, The LED only needs minimal lumonsoity.
> > Enough for the receiver, but not so bright as to allow one to see
> it
> > from across the shop. ( I like double or triple powering LEDs
and
> > pulsing the signal to get a remarkable bright display.)
> >
> > Thanks, Now I need to play with inverting and non-inverting
> signals
> > from the parallel port to see what will work with what.
> >
> > Dave
> >
> >
> >
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., "Lee Studley" <indigo_red@q...>
wrote:
> > > Hi Dave,
> > > The optocoupler led is just that, an led like you're thinking.
> > It'll
> > > need a current limiting resister. I'm making the assumption you
> mean
> > > the optos are for contact closure sensing going back into the
> port.
> > >
> > > I think your friend is trying to work up a debounce for the
> switch.
> > > reasons for placing a cap across the switch include:
> > > Eliminate arcing to contacts for higher voltages, and not
really
> an
> > > issue at the <20Ma.
> > > -or- more likely, he probably means it will cause an RC time
> > > constant when the switch is opened and will act to keep the PC
> from
> > > reacting to contact release 'bounce', if the software could
> process
> > > it fast enough, and stretch the 'on' time enough so that the
> > > PC will see the 'contact' if it happens quickly. The cap's
> probably
> > > not necessary, but try/test it both ways. Too large a cap will
> > micro-
> > > weld the contacts upon closure during discharge unless you add
> an
> > > additional small R in series with the cap across the contacts.
> The
> > > led series resistor will be on the order of:
> > > (5v-2.1vledtypical)/0.015mA ~= 200ohms @ 5v. (330 ohms is a
> typical
> > > value for ~9mA @ 5v)
> > > -Lee
> > >
> > > --- In CAD_CAM_EDM_DRO@y..., "turbulatordude" <davemucha@j...>
> > wrote:
> > > > A friend said that I should use a small cap at the switch and
> a
> > > > resistor in the power line (5 volts).
> > > > I assumed that they worked just like a LED. figure current
> and
> > > > voltage then select a resistor.
> > > > Is he correct that a cap should be used too ? And if so,
> should
> > it
> > > > be at the switch or at the board ?
> > > >
> > > > Dave