Re: [CAD_CAM_EDM_DRO] Re: not working!

JanRwl@... wrote:

> In a message dated 8/4/00 12:24:01 AM Central Daylight Time,
> jmelson@... writes:
>
> << If the drivers are opto-coupled, then you may need an external 5 V
> supply
> to supply the positive current for the opto couplers (or you can tie
> into the
> +5 V from a disk drive power connector). If you use an external 5 V
> supply,
> the - terminal of the supply should go back to the ground on the
> parallel
> port. >>
>
> AND, some (older?) PC's will not put-out quite enough current to
> "light up"
> Opto-Isolator LED inputs! A bit of a hassle, but I'd counsel to use
> such as
> a ULN-2003 to enable "sinking" more than a few mA, such as is
> necessary to
> "fire" an opto-isolator!

Right, most PC parallel ports do not SOURCE much current, but can sink
a good deal of current, at least 10 mA, which is plenty for just about
any
opto-coupler. If the software has the polarities working right, you
should
be able to hook external +5 V to the + side of the opto-coupler input,
and the parallel port signals to the - side. The opto-coupler would see

LED on when the parallel port bit is LOW.

Jon