Re: [CAD_CAM_EDM_DRO] Getting Parallel port to run relay

----- Original Message -----
From: "Alan Marconett" <KM6VV@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, January 29, 2005 1:36 PM
Subject: Re: [CAD_CAM_EDM_DRO] Getting Parallel port to run relay


>
> HI Scott,
>
> Perhaps the easiest thing to do to protect the PC is to use
> opto-isolation. Commercial drivers like Geckos have these already.
>
> A series resistor will limit the current, but also drop the voltage. A
> resistor is generally used in the base lead of a transistor driver.
> Also useful in small values to limit ringing of bus lines.
>
> What are you driving? If you need a relay, use a relay driver circuit
> (transistor or IC), or a SSS (Solid State Switch).
>
> If you're driving a stepper driver, then you might want to use a
> "Parallel Line Extender", like Bravo sells. This provides driver ICs to
> help isolate the PC, and also provides additional driver current for
> long lines.
>
> Another good way to protect the PC is to use a "plug-able" parallel port
> card.
>
> The best way would be to use an "industrial interface card". (expensive).
>
> Haven't seen any fuses that would protect a port line. Keyboard, yes.
>
> A choke would be an inductive load, and would actually MAKE a spike! A
> diode would only allow current in one direction. Would work a little
> like a diode across the coil of a relay (inductor!).
>
> HTH
>
> Alan KM6VV
>
>
> Scott L Golden wrote:
>
> > I may be way out on a limb here but can't one put fuses in line? I admit
low
> > amp fuses but wouldn't that help with spikes?
> >
> > Now go easy on me... I am not too deep into electronics.
> >
> > Or isnt there a one way choke or something to limit the flow of power
> > backwards?
> >
> > Sorry for the lack of knowledge but....my thoughts anyway. lol
> >
> > Scott L Golden
> > Never Give Up
> >
> >
> >
> > ----- Original Message -----
> > From: "Andy Wander" <awander@...>
> > To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> > Sent: Friday, January 28, 2005 3:27 PM
> > Subject: RE: [CAD_CAM_EDM_DRO] Getting Parallel port to run relay
> >
> >
> >
> >>Alan:
> >>
> >>I'm talking about the huge inductive "spike" that occurs when the
> >
> > "control",
> >
> >>whether it is a switch, a parallel port pin, or whatever, opens the
> >
> > circuit.
> >
> >>This causes a voltage spike that WILL fry transistors!
> >>
> >>But the OP has indicated that he DID have a suppression diode installed
> >>across the coil, so that is probably not the problem.
> >>
> >>
> >>And it is very possible to control relays with the parallel port
directly;
> >>I'm controlling some small 5V relays directly with my parallel port. You
> >>just nned to make sure that the relays source less current than the port
> >
> > can
> >
> >>sink(low-active is recommended).
> >>
> >>
> >>
> >>Andy Wander
> >>Verrex Corporation
> >>
> >> -----Original Message-----
> >>From: Alan Marconett [mailto:KM6VV@...]
> >>Sent: Friday, January 28, 2005 3:02 PM
> >>To: CAD_CAM_EDM_DRO@yahoogroups.com
> >>Subject: Re: [CAD_CAM_EDM_DRO] Getting Parallel port to run relay
> >>
> >>
> >>Hi Bert, Andy, list,
> >>
> >>After thinking about it, I wonder if simply connecting a parallel port
> >>output pin to a relay coil would damage it. It wouldn't work, mind you,
> >>but relay coil will still offer some resistance, and the current flow
> >>will be limited. If the other end of the coil is grounded, then a HI on
> >>the pin will typically have minimal source capability. If the other end
> >>of the relay is connected to +5, then the pin will try to source
> >>probably 20-30 ma. What was the voltage/current rating of the relay
> >>coil? Provided the coil was not not left "energized" for a long
> >>period, no damage may have been done. Give it a check with an LED and a
> >>220 ohm resistor!
> >>
> >>Alan KM6VV
> >>
> >>
> >>Andy Wander wrote:
> >>
> >>
> >>>If you hooked a relay up to your parallel port, and you didn't install
a
> >>>diode or other suppression device in parallel with the relay coil, then
> >>
> >>you
> >>
> >>>may have fried your printer port pin. When a coil has a field set up in
> >>>it(by having current flow through it), opening a contact(your port pin)
> >>>stops the current flow and causes the field to collapse, generating a
> >>
> >>large
> >>
> >>>reverse current through(and hence a reverse voltage across) the coil.
If
> >>
> >>not
> >>
> >>>shorted through some sort of snubber circuit(I use a reverse-biased
> >
> > diode)
> >
> >>>this can cause switch contacts to arc, and can also blow out transistor
> >>>circuitry.
> >>>
> >>>This is the same principle used to generate high spark plug voltages
> >
> > using
> >
> >>a
> >>
> >>>DC battery in your car(ok, I know the new cars may use a different
> >
> > method,
> >
> >>>but this is the traditional methed)
> >>>
> >>>Andy Wander
> >>>Verrex Corporation
> >>>
> >>>
> >>> -----Original Message-----
> >>>From: bertmantx [mailto:bertmantx@...]
> >>>Sent: Thursday, January 27, 2005 10:06 PM
> >>>To: CAD_CAM_EDM_DRO@yahoogroups.com
> >>>Subject: [CAD_CAM_EDM_DRO] Getting Parallel port to run relay
> >>>
> >>>
> >>>
> >>>Looking for any advice an how to get parallel port to activate relay
> >>>to start plasma torch. Inatalled PC relay (which I now know to mean
> >>>Printed Circuit) and tried running it direct from parallel out put.
> >>>All was well for about 20 cuts and then it just stayed on. If it is
> >>>off when hooked up will stay off until turned on then stays on. Have
> >>>tried hooking NPN xsistor with Game port 1 to coil, coil to
> >>>collector and emitter to ground. 1K resistor between parallel signal
> >>>and Base. No response when hot signal (verified +5.9v) touched to
> >>>resistor or direct to base of xsistor. If shorted from collector to
> >>>base will trip 20 or so times then nothing. Remaining Para ports are
> >>>running motors fine.
> >>>
> >>>Any thoughts on damage to computer?
> >>>
> >>>Any pointers on assessing computer damage?
> >>>
> >>>Hard to believe there isn't a plug and play device just for this,
> >>>but have had no luck finding anything.
> >>>
> >>>First cuts looked surprisingly good and had High hopes. Depression
> >>>is now setting in quickly.
> >>>
> >>>Any advice greatly appreciated.
> >>>
> >>
> >>
> >>
> >>
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for OT
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subjects, that are not allowed on the CCED list.
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> 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
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> 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........
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