Re: Parallel Port to Power Supply Grounding Differential

Hi Bill,

The PC to Gecko can be direct and in fact some breakout boards with
opto isolators may add propagation delays on the pulses.

The next part is your outputs for coolant and spindle and whatever.
typically 4 outputs. Many of us use solid state relays and those are
also isolated, again no problem.

then the 3rd set of I/O's are your home switches. here you might
have a 5v line from the PC, across the gantry, past your
stepper/servo wiring, past your 110 spindle wiring and all the way to
that end/home switch.

THAT line is at risk.

By using an opto on that line, you isolate it from your PC and keep
everything to itself.

I made a breakout board for my use that has a wall wart for powering
those 5 input lines for the home/end switches.

I used a darlington to power the on-board relays, and that darlington
has enough power to switch slightly larger loads than the DIN relays
I used. If I used the Solid State relays, the darlington is not
needed.

I did the board in the propritary and free, ExpressPCB so it is not
in a Gerber format or even a G-code.

Dave






--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Bill Kichman"
<billkichman@c...> wrote:

> Thanks for the clarification... I am also planning to use Mach 1 or

similar

> app, and will need to interface the limit and other safety

circuits, which

> makes the necessity to connect to an outside ground a greater

possibility.

> Bear with me while I go over my setup.....I am using (2) toroid

transformer

> power supplies with secondaries completely ground isolated from the

AC

> supply, and currently the DC negatives are chassis connected. At

present the

> AC chassis ground is not connected to the case (although likely

should be

> eventually for safety). I took a look at the parallel port

grounds, and

> they are tied in common with the PC chassis ground, at the

backplane metal

> connector.
> If I were to install a separate permanent cabled ground, say a

stranded

> #14AWG, between the PC and the DC supply ground, and ensure it was

always

> connected before powering either device, wouldn't that take care of

the

> problem? That is, if I ensured I am powering from the same AC

socket, can't

> I reasonably expect the grounds to be at the same potential,

although there

> will possibly be some ground current through the ground connection?
> Additionally I can use a laptop possibly as a controller, which is

fed from

> an isolated wall cube of course, so isn't that similarly approached?
>
> If I really need a breakout board I 'll get one, but I want to be

sure why I

> am doing this and what other corrections can be made to correct the
> potential problem. Thoughts?
>
>
> R. William Kichman, P.E.
> Kichman Engineering Associates
> 103 Old Furnace Road
> Cornwall, PA 17016-0643
> tel/fax 717/270-0714
> ----- Original Message -----
> From: "Jon Elson" <elson@p...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Tuesday, July 08, 2003 1:06 AM
> Subject: Re: [CAD_CAM_EDM_DRO] Parallel Port to Power Supply

Grounding

> Differential
>
>
> >
> >
> > Bill Kichman wrote:
> >
> > >Just wondering how other folks are ensuring they don't blow out

their

> parallel ports via voltage differentials between the parallel

port's #18-25

> ground pins and the chassis ground at the power supply case? I am

using

> Gecko 320's and a spare PC case housing a transformer fed linear

75V power

> supply (minus grounded to case) and (3) servo drives with rotary

encoders. I

> measured the voltage differential between the power supply grounded

case and

> the parallel port cable's grounds and measured about 3V. I guess I

can

> manage to keep these grounds separate, since the Gecko uses opto-

isolated

> interfaces, but should the (2) get inadvertently connected, I

wouldn't want

> to "release the smoke genie". I read somewhere that somebody sells
> optoisolated breakout boards, but the (2) I could find in my search

were not

> isolated. What are my options?
> > >
> > >
> > The Gecko drives all use opto-couplers to isolate their inputs

from the

> > motor power
> > supply. The proper wiring is to use the +5 V from the computer

(either

> > game port
> > or a disk drive connector) on Gecko drives set up for a positive

common

> > terminal
> > for the optos. There should be no connection to the grounds of

the

> > parallel port.
> >
> > If you have the Gecko drives that can only work with a negative

common

> > terminal,
> > then that common should be connected to the parallel port's

ground. You

> > will
> > likely need pull-up resistors from the step and direction signals

to a

> > +5 V derived
> > from the computer as above.
> >
> > You should not make any other connections between the parallel

port and

> > the Gecko
> > drives. You can ground the DC - on the Geckos to the power

supply case,

> > and have
> > that ground connected through the safety ground pins of the wall

socket.

> > This
> > single-point ground avoids ground loops as much as possible.

Since the

> opto
> > isolators withstand at least 1000 Volts, the 3 V offset you

measured

> > should be
> > of no concern. If you use a shielded cable between the computer

and the

> > Gecko
> > box, the current will flow ONLY through the CASES of the

equipment, not

> the
> > circuit boards (assuming things are built right). This will not

harm

> > the equipment
> > in general, but could cause problems when cables are connected and
> > disconnected.
> > It would be best practice to have the computer and the Gecko box

plugged

> > into the
> > same outlet to avoid ground loops in this case.
> >
> > Jon
> >
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
> > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> > Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
> >
> > Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> > Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> > List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com,

wanliker@a...,

> timg@k...
> > Moderator: pentam@c... indigo_red@q... [Moderators]
> > URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
> >
> > OFF Topic POSTS: General Machining
> > If you wish to post on unlimited OT subjects goto:
> aol://5863:126/rec.crafts.metalworking or go thru Google.com to

reach it if

> you have trouble.
> > http://www.metalworking.com/news_servers.html
> >
> > http://groups.yahoo.com/group/jobshophomeshop I consider this

to be a

> sister site to the CCED group, as many of the same members are

there, for OT

> subjects, that are not allowed on the CCED list.
> >
> > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY

POSTING THEM.

> DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> > bill
> > List Mom
> > List Owner
> >
> >
> >
> > Your use of Yahoo! Groups is subject to

http://docs.yahoo.com/info/terms/

> >
> >