Re: [CAD_CAM_EDM_DRO] limit/home switches

Matthew King wrote:

> Question for you EMC guys - do the various switches need to be opto-isolated
> from the parallel port, or can the simply be hooked directly to their
> respective pins?

You can do it directly. there is some safety for the computer to
be isolated from the switches. If cables were to get caught on a
sharp edge and cut, stepper or servo motor power could get crossed
with the limit switch circuit. if it is not optoisolated, a complete new
computer (power supply, motherboard, memory, CPU chip, disk drives,
etc. is a possibility) might be needed. I did see someone do this
on an old 16-bit minicomputer, smoke, bits of chips flying around
inside the cabinet, etc.

> Does the parallel send/receive 12 or 5 volt signals?

5 V signals only.

>
> If 12v, can one power the switches from a seperate power supply and hook
> them to the individual pins, i.e. pin 10 for the limit switch? I can get 5v
> from the same power supply easily enough, assuming the switches already on
> my mill (series one cnc) are 5v.

Yes, you could do it this way, with the 5V power supply.

Jon