Re: [CAD_CAM_EDM_DRO] Re: Parallel Port Interface

currinh@... wrote:

>
> For what it is worth, here's what I've done.
>
> I designed and built the opto-isolation circuit (quite
> an accomplishment for me) and this worked well. However,
> it inverted the signals and EMC did not like this.
>

I think I suggested this idea before (using single ended signals,
buffering them to higher strength, and using a Schmitt trigger
type device (with built in hysteresis):

Using a 74LS132 quad 2-input positive NAND Schmitt trigger TTL
chip (under a buck), you can use it this way:

As it is a NAND, if you hook one input up to GND and the other
input to your signal (and I am presuming this chip is right next
to the encoder, for buffering the signal down to your driver/PS
box), then you get:
- the buffering
- Schmitt trigger hysteresis (good for noise reduction)
- the signal is NOT INVERTED.

However, if you do want the signal inverted (to fix the problem
above where EMC, or some other program, doesn't like it some
particular way) hook one input up to +5, and the other input to
your signal, then you get:
- the buffering
- Schmitt trigger functionality
- the signal is INVERTED.

In fact, since the chip has 4 NAND circuits, you can hook a
circuit up both ways when you originally solder it together,
and select what you want (Inverted or Not Inverted) to suit
the circumstances.

Doug Fortune
http://www.cncKITS.com