RE: Need help with parallel port input design

Jeff,

I think an opto-isolator is overkill. I would suggest using a 7404 or 4069
hex inverter, to accomplish the same thing. Both are very cheap. Download
the PDF (google, "7404 pdf" or "4069 pdf") and see what pins are what.
You'll figure it out.

Use a 7805 voltage regulator to get the power from the 12V source down to 5V
as well. And to clean up the power, place a 10uF cap across the output and
ground after the 7805.

A resistor network of 10k ohm will help pull up the current to 5V as well.

Depending on how quickly you want this board, I would recommend Dean
Coullard's break out board. It's well made and clean, and simple.
http://members.shaw.ca/axxus/db1v20.htm . I asked him last week, he was out
of stock, but will be getting some in soon.


I bought one, and am very happy with it. It made things a lot easier to
wire up.


Cheers.
Lloyd,
Toronto



-----Original Message-----
From: washcomp [mailto:jeff@...]
Sent: September 15, 2003 4:50 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Need help with parallel port input design

I'd like to provide opto-isolation to the 5(?) input pins on a
parallel port used to monitor limit switches. I understand that I'll
also have to provide some resistors? What's the easiest way to do
this? I looked at the Digikey catalog and they offer about 4 million
opto-isolators of all types, but I'm kinda clueless about which to
use or an actual circuit to make use of the right one. Any help
would be appreciated. I've bought an 8 port parallel relay board and
figure I can retrofit this to the input pins (they are currently not
connected on the relay board, but it has a 12v DC supply built on).

Thanks and regards,
Jeff