RE: [CAD_CAM_EDM_DRO] LPT question from newbie

> I was hoping someone could help me with this. I use a
> PMDX-120 to isolate the computer I'm working with. When I
> plug it into a computer at work, Relay A is off, the rest are
> on. When I plug it into a computer my school provided, ALL
> relays are on. This is most distressing since I am using
> Relay A to power a VERY small motor (ON/OFF, no speed
> control) I can't change the state of the relays that are on
> when plugged in.

What pin on the parallel port is used to control relay A? Is it one of the
data lines, or something like strobe?

In theory, all parallel ports are supposed to initialise to the same state,
however some people have observed some ports change state as the PC boots
up, pins will go high then back to low, etc. Some controls boards handle
this, some don't. The ones that do are inactive until they detect a certain
signal on a certain pin, this is sent by the software on the PC.

The best test is to turn on each PC with nothing plugging in, and check the
state of the lines. You can use a multi-meter or even a LED, and active pin
will be set to 5v. (Maybe 3v, like some laptops do). Then watch what
happens when you turn the PC off then on.

You could always run your motor off relay B, and treat A as a lost cause.

Tony