Flood sensor

Hard to do something that's totally immune from critters and creepers. A float switch might be the simplest "close enough" solution that you could periodically open to clean out accumulated gunk.

I'd go with something like your idea: a shell of perforated PVC pipe wrapped in a layer or two of fine nylon mesh (i.e., used hosiery), a donut-shaped float that has a magnet (or two) embedded in it, and a central shaft with a magnetic reed switch inside it. Back it up with a couple of conductivity probes set at about the same level as the reed switch.

--
Rich Webb   Norfolk, VA

road

front

them.

not

be

Not a problem.

Glue your arse to the pavement and if you find that the navy has parked a ship on your face then you're flat.

DNA

Maybe just use some kind of submersible pressure sensor?

--Mac

road

front

them.

general

give

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would be

Something that would register perhaps 0.01 bar (3 or 4 inches or so of water ) may well be triggered by an amorous snail or the like. So far I'm thinking of a fully exposed float switch I can keep a fairly regular eye on, anything enclosed is bound to fill up with various forms of gunge.

Put the pressure sensor in an air-filled bladder. It would have to be a pretty heavy snail to set it off then. Also, if you have multiple sensors at multiple low-points, you can reject false positives, somehow.

--Mac

Float switch would seem to be the simplest solution. To keep critters and assorted detritus from jamming it, make the float big. Heck, it can weigh a couple of tons, just as long as its buoyant. Attach it to some sort of switch mechanism. If this is for some sort of alarm, consider a one-shot arrangement. Possibly a wire that is broken or unplugged when the float floats.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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During the next two hours, the system will be going up and down several
times, often with lin~po_~{po ~poz~ppo\~{ o n~po_~{o[po  ~y oodsou>#w4ko

I've had success in 'dirty' sumps etc by using an old dishwasher level pressure switch. If you mount it on say a half inch coupling and then about six inches or more of two inch pipe below that (use an adaptor) it will be sensitive and reliable as well. Naturally the switch would be in a suitable enclosure :-)

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Regards ......... Rheilly Phoull

general

give

would

about

suitable

Using a hose full of water and 2 bits of clear polythen tube i've determined the front garden is lower than the back. Also i can then use the existing front doorbell as the alarm if using a simple float switch, less likely to fail unnoticed if there is a power problem with a separate alarm system. I think a pit covered in 1/2 inch mesh to keep rats and hedge-hogs out , a few crystals of sodium chlorate every now and then to keep the weeds out and a bit of string tied to the swing arm of the otherwise water sealed float switch, to test every now and again, would be the most reliable.

Your water has a high salt content and is therefore well suited for a detector switch based on conductivity. A totally impervious and sealed system would be the coupled coil technique using transmitter/receiver toroidal wound cores on same axis and separated by a small distance. When the axial path between coils is submerged in relatively high conductivity material, sea water is 5S/m, alternating magnetic field in the transmitter coil induces a current in the water flowing in a solenoid path about both coil axes when joined by the water. This current induces a magnetic field and therefore voltage to be detected in the receiver toroid. Everything can be enclosed in PVC and thresholds set to avoid false alarms due to point objects and vegetation. It does require power but it is not necessary to measure continuously, it could go into sleep mode and wake up every 10 minutes for a few milliseconds or so, ensuring long battery life. It should be a relatively low technology project, and there may even be some design ideas on the web.

. .

. .

I would go for four float switches this size and put one under each corner of the house. Then when the water rises the house will stay above it!!

--
John B

I like the idea of it being sealed and no moving parts. With a float switch and a ground frost it would fail but I cannot see it remaining frozen when inundated. On the negative side a slug may take a fancy to the sensor and pehaps falsely register as water, also more difficult for testing than just pulling a bit of string.

A time honored inexpensive method is to simply place an ordinary aspirin tablet between two spring loaded contacts. When water reaches the aspirin tablet it disolves or crumbles, allowing contact to made to sound an alarm or whatever.

An ideal fixture of this type can be easily made using one of those spring loaded twin-lead clip-on connectors once in common use by TV repairmen (if you can still find them today). Another possibility is to add contacts to a spring type clothes pin (these are still available), and pinch the tablet between the jaws.

Yes, pretty crude I know, but the method has worked quite well for nearly 50-years. :-)

Kindest regards, Harry C.

p.s., I have no idea why aspirin is the tablet of choice for this method, since anything soluble in water would appear to work just as well.

I suspect because of availability, it having been used in the past as a contraceptive.

Paul Burke

In response to what Paul Burke posted in news: snipped-for-privacy@individual.net:

When held between the knees?

--
Joe Soap.
JUNK is stuff that you keep for 20 years,
then throw away a week before you need it.

Bwahahahaha! Good one!

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

How about a washing machine water-level switch? It's a pressure activated switch over a tube that dips into the water. Keeps the water away from the switch.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Yabbut, only if you've never heard of "doggie style". ;-)

Cheers! Rich

OK, I'll play straight man here.

Question: So, does one take the aspirin before or after sex?

Answer: Instead of.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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Drugs may be the road to nowhere, but at least they're the scenic route!

[snip]

This should work well. The only drawback I can think of is if the water level comes up very slowly. The air trapped in the tube might dissolve in the water. I'm guessing that this would be a factor if the level rose over several days.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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Speed is n0 subsittute fo accurancy.