Lightning immunity for a computer connected to a weather station?

My problem is that I am building a remote weather station, which will be stationed up on my roof once it's completed. I've chosen to connect it to my computer through the serial port (RS-232), mainly for financial reasons and simplicity. I always figured that once I got it working with the serial port, I could worry about making it lightning-proof later.

I've already purchased the microcontroller board (which is serial port only!), but I haven't started building the system yet.

So now my options are, I suppose:

1) Buy a new microcontroller board that has Ethernet, then connect it to a wireless transceiver which will then connect to my wireless home network (expensive).

2) Create an RS-232 to fiber optic link, have 2 transceivers at either end of a long fiber cable which convert the signal back to serial (time consuming).

3) Buy an off-the-shelf serial-to-wireless system (very expensive).

Ideally I don't want to have to do any of these things. What if I simply grounded the weather station, would that work? I don't care about the weather station getting damaged from a lightning bolt, I just want my computer and home to be safe...

Any thoughts, ideas?

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MT

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mark thomas
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Of course grounding the weather station thoroughly and locally is a good idea.

You might start with an opto isolated RS232 interface (up to about

5000 volt protection) using a pair of optos for each line. Wire the two LEDs inverse parallel and stack the two transistor outputs in series across +- supply. This is not strictly an RS232 DC modem but it can work for pretty significant baud rates.

These should work:

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You get maximum isolation by bridging across an actual slot under the chip.

--
John Popelish
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John Popelish

Lightning gonna go where lightning wanna go!

If you get a strike on your sensor setup on the roof, it's gone. I know people with wireless Davis systems (such as the Davis Vantage Pro) that have been hit. Wireless -- no connection between the measuring instruments on the mast on the roof and the receiver. A strike, and the thing on the mast is reduced to slag, no matter what. The wireless receiver, if the house wiring, etc., was kept out of the strike, was fine.

Do your best. Insure the rest.

Reply to
artie

You just tossed out two excellent solutions.

Reply to
Robert Baer

I don't think you will be able to do this without any effort/money at all.

Copper cable is cheapest but could guide lightning into your home.

It should not be too hard to do the fibre optic idea. Get the RS232 to drive LEDs, and have a simple light to +/-12V (or even

+/-5V) sensor at each end. If your station is a microcontroller, it can discard the RS232 buffer chips and interface the opto signals directly to logic.

As for the radio link, there are simple low-power data links available.

418 MHz IIRC.

My suggestion would be to communicate using infra-red remote-control components. These are dirt cheap and simple. The range is far enough to get through a window and several metres of air, which should be a safe enough isolation gap.

Tx is a simple IR LED, maybe with a small transistor. the micro controller simply drives it at 36 kHz carrier, the modulation could be a handset-style protocol.

You can lift a suitable sensor and IR filter off an old bit of consumer equipment.

BTW how are you getting power to the thing? Lightning will zip through power cables too, though wall-warts are cheap to replace.

If you power it off a solar panel and lead-acid battery, note the latter will need replacing every few years. The former may need mounting in such a way that rain will wash grime and bird shit off. Maybe a daily burst of windscreen-wiper activity?

Reply to
Kryten

Lightning immunity is about the same principles that Ben Franklin demonstrated in 1752. Incoming wire from station must first drop down and connect to the building's single point earth ground. Every wire must connect to that ground either by direct connection or via a surge protector. Why? Surge protector is not surge protection. The earth ground rod is surge protection.

Idea is quite simple. Either lightning will find a path to earth via your computer, or it will find a shorter path via that ground rod. Details posted in "Thunder and Lightning" in alt.support.sleep-disorder on, before and after 24 June

2001 at
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RS-232 has distance limitati> My problem is that I am building a remote weather station, which will

Reply to
w_tom

Be my guest -- glad to have provided some amusement.

--
Namaste--
Reply to
artie

ROTFLMAO! May I sig this?

Andreas

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A wise person avoids it.
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Reply to
Andreas Hadler

....and how is the instrumentation going to be powered? Rechargeable batteries? Ball lightening? Tesla's "eek" hair?

Reply to
Robert Baer

Yes; RS-232 has a limit of a few miles (when done properly). But i do not think he means to run RS-232 wires more than a few hundred feet.

Reply to
Robert Baer

At the risk of sounding pedantic, RS-232 is not running over those few miles. It only runs to the modem. RS-232 was originally written as the specification for signals between a Data Terminal device (your computer) and a Data Communication device (you modem). When the spec was written, it was assumed that pairs of modems would be connected by something much like the public telephome network of the time, but it could be anything - coax, twisted pairs, optical fibers, microwaves...

To really be pedantice, the proper name now is EIA-232.

Reply to
Richard Henry

Reply to
w_tom

RS-232 is will perform data transmission for miles when using modems at each end. Then it is typically good for something like 3 or 5 miles. Quite doubtful the weather station is using a modem. Serial port drivers and receivers are typically good for under 100 feet. Longer distances may result in excessive noise because RS-232 serial port drivers are common mode.

Greater distance with less noise is > Yes; RS-232 has a limit of a few miles (when done properly).

Reply to
w_tom

OK thanks everyone for the input...

So, does grounding the weather station make it more succeptible to lightning strikes?

If I don't care about damage to the weather station and use fiber optic which doesn't conduct, is there any point in grounding the weather station?

Even if I ground the weather station, will it still get just as damaged as if it weren't grounded when lighting hits it?

Which of these 3 scenarios do I do?

1) Ground the weather station, keep using RS232 cabling (least time consuming) 2) Don't ground the weather station, use fiber optic cabling 3) Ground the weather station and use fiber optic cabling (most time consuming)
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MT

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mark thomas

| At the risk of sounding pedantic, RS-232 is not running over those few | miles. It only runs to the modem. RS-232 was originally written as the | specification for signals between a Data Terminal device (your computer) and | a Data Communication device (you modem). When the spec was written, it was | assumed that pairs of modems would be connected by something much like the | public telephome network of the time, but it could be anything - coax, | twisted pairs, optical fibers, microwaves... | | To really be pedantice, the proper name now is EIA-232.

I'm using an embedded serial driver, so I am limited by 50-100feet, which is more than enough to reach my roof from my computer...

Anyways I don't have a choice, I purchased a microcontroller board that uses RS232, not RS485. And, this isn't really what I was asking.

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MT

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| Kryten wrote: || || I don't think you will be able to do this without any effort/money at all.

Agreeable, I just want the solution involving the least effort/money.

|| Copper cable is cheapest but could guide lightning into your home. || || It should not be too hard to do the fibre optic idea.

My main beef with this solution is I'm doing this mainly as a software project, not a hardware project.

|| Get the RS232 to drive LEDs, and have a simple light to +/-12V (or even || +/-5V) sensor at each end. || If your station is a microcontroller, it can discard the RS232 buffer chips || and interface the opto signals directly to logic. || || As for the radio link, there are simple low-power data links available. || 418 MHz IIRC. || || My suggestion would be to communicate using infra-red remote-control || components. || These are dirt cheap and simple. || The range is far enough to get through a window and several metres of air, || which should be a safe enough isolation gap.

I can't use infrared because the weather station is on my roof, there's no line-of-site unless I walk outside.

|| Tx is a simple IR LED, maybe with a small transistor. || the micro controller simply drives it at 36 kHz carrier, || the modulation could be a handset-style protocol. || || You can lift a suitable sensor and IR filter off an old bit of consumer || equipment. || || BTW how are you getting power to the thing? || Lightning will zip through power cables too, || though wall-warts are cheap to replace.

Good point. The microcontroller comes with a normal transformer 12VDC power cord, which I was planning on using... I'll use batteries if I have to.

|| If you power it off a solar panel and lead-acid battery, || note the latter will need replacing every few years. || The former may need mounting in such a way that || rain will wash grime and bird shit off. || Maybe a daily burst of windscreen-wiper activity? | | ....and how is the instrumentation going to be powered? | Rechargeable batteries? | Ball lightening? | Tesla's "eek" hair?

If I want to plug it into my house's power, how do I do this safely? I'll use batteries if there's no other option.

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MT

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mark thomas

Did you read my reply? You should not only ground the weather station, but put a lighting rod above it to carry away most of the current or anything like a direct strike. You don't want that passing, willy-nilly through your house. This grounding system should tie to the power entrance ground, so that there is a limit on the voltage between various parts of your home system.

You limit the voltage peaks on the signal lines with surge suppressers (grounded to the same line that grounds the lightning rod and weather station) and isolate the signal lines with opto isolators to handle the bumps that get past the front end grounding. Your whole house will benefit from these provisions.

--
John Popelish
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John Popelish

| Did you read my reply? You should not only ground the weather | station, but put a lighting rod above it to carry away most of the | current or anything like a direct strike. You don't want that | passing, willy-nilly through your house. This grounding system should | tie to the power entrance ground, so that there is a limit on the | voltage between various parts of your home system. | | You limit the voltage peaks on the signal lines with surge suppressers | (grounded to the same line that grounds the lightning rod and weather | station) and isolate the signal lines with opto isolators to handle | the bumps that get past the front end grounding. Your whole house | will benefit from these provisions.

OK, thanks a lot for your replies. I think they were the most helpful, I just like to explore every possibility before making a decision. The problem with using opto isolators is that now I need build a new circuit at the computer end, and I'm on a tight schedule (it's for a school project).

For the surge suppressor, do you think the SMDA12C-5 is a good one?

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Or should I just go with something simple like this:

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Also, WRT connecting *everything* including the lightning rod to the power entrance ground, isn't this the same ground that is in every power outlet in the house, or do I actually need to connect to the power breaker? (this is out of my range of abilities). Sorry for the lame questions. I'm a software engineering student, not an electrical engineer.

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MT

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Sorry, I'm replying to my own post... | The artist formerly known as John Popelish wrote: | || This grounding system should || tie to the power entrance ground, so that there is a limit on the || voltage between various parts of your home system. || || You limit the voltage peaks on the signal lines with surge suppressers || (grounded to the same line that grounds the lightning rod and weather || station)

Everything I've read says to ground the lightning rod into the soil.

Also, I think since I don't care about the weather station being damaged, I'm just going to go with the opto isolators, and forget about the lightning rod and surge suppressor.

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MT

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mark thomas

Small potatoes compared to replacing the motherboard. RS232 was designed to be contained entirely in a single room. It contains not protection for surges.

Too puny.

Also puny.

I would get something like a SA15CA (on each side of the isolator) for each line (except ground which breaks across the isolators):

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The ground for each of these should go back to the signal ground at the equipment.

The lightning rod should go as directly as possible with a healthy (#8 or larger) copper wire to the service entrance, all outside the building. Feel free to add an extra ground rod (or two) to that node, also. If your water piping system is metal, make sure it also ties to the service entrance ground. If the lightning rod gets a big thump, the whole house electrical and plumbing system will bounce, mostly in unison, preventing large voltages from existing between different parts of the system (even though the instantaneous voltage with respect to Earth may be significant till the ground rods drain the charge), with only minor ringing between parts that causes brief and smaller voltage difference in different parts of the system (the weather station and your computer, for instance.

The equipment (and, thus, the suppressor) grounds can get back to that common point via receptacle grounds. The 15 volt surge suppressers clip the peaks from this ringing, only, not the lightning pulse.

Don't forget to add a grounded suppressor to the phone line at the service entrance before it is routed to any phones or computers. Same for cable TV.

This sort of system has a fair probability of surviving an ear splitting hit.

Leave out any parts of this and the probability or survival goes down.

--
John Popelish
Reply to
John Popelish

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