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steve_b
08-27-2004, 10:42 PM
Hey guys,

i'm looking at putting some lightning protection one of my rs232 lines coming from a sensor that I have up in a tower.

as it is, I'm only using the Gnd and Tx lines coming from the stamp.· I was wondering if anyone knows of a nice rs232 optical isolator.

Basically, I don't want to kill my big fancy shmancy computer if lightning gets down my line and in to the PC.· So something to install at either end would be great.

I've googled a couple....and am looking at Analog Devices (ADuM1200) Dual Channel digital isolator...of course, now that I'm thinking, digital level being 5Vdc, that this probably won't work....ah well.



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Steve
http://members.rogers.com/steve.brady (http://members.rogers.com/steve.brady)
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"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Buck Rogers
08-27-2004, 11:07 PM
Hello from Buck Rogers
Steve, Maxim http://www.maxim-ic.com·makes a bunch of RS232 devices. That list contains a few such devices, one has partial isiolation, and another has full isiolation. Supposedly the isolation on them is right up there with the isiolation on the optoisolators, like the 4N33. The last time I checked it was rated for about 1500 volts. I don't think that's up to preventing the hardware from getting fried by a lightning blast, but you never know.....

Buck Rogers
http://www.gregg.levine.name

DntGvaSht
08-28-2004, 05:54 AM
I would think the best way to seperate your PC from millions of volts would be to use fiber-optic cabling.· You could run a long length right up into the tower, and have an expendable power supply to run it.

Just a suggestion

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Alan Bradford
08-28-2004, 06:11 AM
Hello,

The best way to isolate the millions of volts from a direct lightning strike would be to use a fiber line driver at each end and as much fiber optic cable as you can afford. Look to www.blackbox.com (http://www.blackbox.com) for commercial RS232 to Fiber Drivers. in the $150-$350 range, and you need one at each end. The fiber cable is about $59 + $1 per foot.

A $2 isolation IC will not stop voltages that can jump distances that are rounded off to the nearest foot. Dont fool yourself, there is no free lunch where lightning protection is involved.

Hope this helps,

Alan Bradford

Plasma Technologies

steve_b
08-28-2004, 08:20 AM
I like the idea of using fiber...but, it's a 150ft run through conduit and we're borrowing some spare wires.· So, it's more trouble to run another cable that needs to be protected (if we ever run another cable within the conduit that happened to have fiber, I'd be worried about damaging the fiber -- I know there isnt' just a single fiber wire but 15 or 20)



Anyhow, I'm looking more for just something I can add to my current install (which is on copper).· I've thought about MOV's and some sort of GAS ionizing device (can't think of the name but I've used TII or TTI's which shunt to ground through ionized gas)....but these all have transition times and the PC I'm using is an industrial PC worth a few bucks! http://forums.parallax.com/images/smilies/tongue.gif

optoisloation seems to be the sure way to make know there's separation between the outdoor tower run and the PC.





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Steve
http://members.rogers.com/steve.brady (http://members.rogers.com/steve.brady)
http://www.geocities.com/paulsopenstage (http://www.geocities.com/paulsopenstage)

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Alan Bradford
08-30-2004, 02:23 AM
Hi,

You can still add fiber. WHen the Copper enteres your building, or exits the conduit, use the fiber driver and then 20-50 feet of fiber to the PC. You can still protect the PC and not have to run out to the tower. I would reccomend at least 10 feet of fiber from the conduit to the PC.



Hope this helps,

Alan Bradford

Plasma Technologies

steve_b
09-02-2004, 10:35 PM
Hey guys,

just threw together a quick cct that I partically got off the net.

Uses a MAX232CPE transceiver chip and a 4N35 opto IC.

With some caps and a couple resistors I was able to get her running.

My only issue right now is that (as you'd see in my sandbox post about laptop rs232 voltage levels) that I need to power this cct and to steal power from the status lines won't work while using a laptop.· All status voltages on my laptop are 5-ish volts (dc of course).· Sure, I can power the cct directly but who's to say this doesn't find it's way over to a desktop PC where there are real RS232 voltages.· Would hate to let the smoke out of the rs232 IC (opto specs say it could handle it).· So, I put in a 5V regulator and found that it works great but not off these status lines (regulator needs to have Vinput >1.7V of regulated Voutput).

So, although I have protection.....I don't like I may have to use a clunky wallwart to ensure this cct survives different PCs.

Of course, I did just use a MAXIM ICL7662 CMOS voltage converter for a solar panel setup (needed +24V for one device).
These are neat little devices, but you do need some good filtering on the output as this is basically a switching cap dump setup.
Anyhow, any ideas would be appreciated!
here's a cheesy little jpg of the cct.http://forums.parallax.com/images/smilies/freaked.gif




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Steve
http://members.rogers.com/steve.brady (http://members.rogers.com/steve.brady)
http://www.geocities.com/paulsopenstage (http://www.geocities.com/paulsopenstage)

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

steve_b
09-03-2004, 10:18 PM
Ok, I took a better look at my cct in the previous post and well....slight oops!



What I was doing was running the data line from outside in to a max232 chip and then grabbing the TTL out and putting that through an opto.

The output from the opto (TTL) was then reingested in to the SAME max232 chip and spit out as proper RS232 to our indoor PC.

I had also ran the Gnd from the outside run in to the common buss ground that everything else was plugged in to....so basically, if lightning (or surge) were to hit the tower, the data line would be protected, but the gnd line would carry the surge all the way in to the inside PC and doing damage anyhow.

So, I revamped my cct drawing (and tested it as well) and this actually works better -- as the other cct was inverted my output on me.

I now just take the TxD and GND from the tower and use those levels to "light" up my opto.· Then I connect the other half of the opto to the +5 and Gnd busses of the rest of the cct and go from there.· I just use the opto output (TTL-ish) and ingest that in to the max232 and spit out the corresponding RS232 data.· no inverted signals or anything.·

Now, I've said that this was for lightning and surge....but this current drawing would probably only be effective with surges as a lightning strike would just come in to my project box and arc over (small box so things will be close!).· So, I'm now looking in to putting some tranzorbs or MOVs in cct too.



Anyhow, here's the 2nd updated drawing...I'll post another when I get something figured out with the MOVs and Tranzorbs.

Here's a question....(might be rhetorical)....MOVs will open in series with a surge in line.· Tranzorbs will short/shunt?!· So, MOVs I can put in series and Tranzorbs from the lines to ground....BUT, I guess I'd have to run a proper earth/chassis ground as I wouldn't want to shunt a surge from the data line to it's signal ground and blow things up anyhow.....

Thinking out loud a bit....

Ok, here's the drawing!





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Steve
http://members.rogers.com/steve.brady (http://members.rogers.com/steve.brady)
http://www.geocities.com/paulsopenstage (http://www.geocities.com/paulsopenstage)

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Jonny555
09-04-2004, 07:16 AM
Hello, may I intrude ? :)

What about putting a lightning rod in the tower with a heavy guage wire straight to ground?

steve_b
09-07-2004, 08:18 AM
That's already there!

But as you might imagine....there is some noise that gets tossed over to the signal line.· And no doubt it's quite considerable compared to the data levels.....
Is it the Gaussian affect or something like that?· not sure!

There are all sorts of corona affects from lightning...don't need a direct hit to kill my system...just the surge from a nearby strike will get on to the line (to some degree).

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Steve
http://members.rogers.com/steve.brady (http://members.rogers.com/steve.brady)
http://www.geocities.com/paulsopenstage (http://www.geocities.com/paulsopenstage)

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."