detection of rain and close window

I am just speculating here, initially I thought of a rain sensor for irrigation, but these measure quantity of rain in inches and would not be effective for rain detection.

A humidity sensor would do the trick and would be more reliable, in theory. Doesn't the humidity peak to 100% when it rains? So you could write a program that say when humidity above 95% close windows, below 90% open windows...

Well according to this site:

humidity may not be 100% when it rains, but it sounds like most of the time it is with more exceptions in the winter.

If you wanted a moisture based sensor try this...

but it would have to be position to get rained on, and you may still have some rain entering the windows. The humidity direction may prove to be better as you could close the window prior to it actually raining, but you may close when it never rains. I guess it is you decision, better to be safe than sorry, or maybe not....

My thoughts would be the temperature/humidity sensor. If you are using an HAI system this allows for more programming as well. If you had heat coils, you can write a program in the winter to melt the snow while it is raining. I have seen this done in Sun Valley, very expensive thing to do, but when you have money like them, who cares...

Brett Griffin, Home Technology Consultant

Architechtronics, Inc. get to know home technology... p. (610) 825.7018 f (215) 827.5484

*top 10 reasons to use Architechtronics for your next project

Not from what I have seen of the sudden blue-sky "summer showers" that the OP was talking about. I'd use the squiggly rain sensors like the one that came with my power casement window kit. They can detect single droplets of water hitting the sensor. I'll dig it out and get the specifics if the OP's still interested.

-- Bobby G.

We need more info to answer your question without needless speculation.

What kind of windows do you have? If you have modern new windows, you may be able to purchase a system directly from the manufacturer. At least Pella and Anderson have a solution for some of their windows and skylights. If you have heavy, old double-hung windows, the solution may be costly and not meet your aesthetic criteria (read ugly).

Are you are handy with making and installing gadgets yourself? Do your own home automation programming? Or you want a turn-key pre-built solution?

In general, one needs:

1) a way to mechanically close the windows (which depends on the type of window),

2) a way to anticipate or sense rainfall (the details for an optimum system depending in part on where you live) , and

3) a decision-making process which might be as simple as a relay connected to sensor or as complicated as computer with multiple inputs running custom software or adapted/scripted home automation control program.

For commercial solution, see

Also

Google this newsgroup ( comp.home.automation ) and the web for "rain sensor window "

HTH ... Marc Marc_F_Hult

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Robert Green wrote:

I'd use the squiggly rain sensors like the one that came with my power casement window kit. They can detect single droplets = of water hitting the sensor. I'll dig it out and get the specifics if the O= P's still interested.

-- Bobby G.

Jim Baber is very interested in what you are talking about in your "power casement window kit" you mention here. Would you please Email info about this kit to him at jim@~~~baber.org.=

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Jim,

Here's the URL:

The sensor I was talking about is in the picture accompanying the item description. It looks a little different than the ten-year-old version that I am using, and the price seems to have gone up quite a bit, but it seems to be basically the same gizmo. If you decide to get one, buy a toothbrush and a big can of Teflon spray lube. The windows driven by the device have to be as clean and friction free as you can make them. Clear out any dust or debris on the window's activating arms and around the seal. Make sure the all of the window's moving parts are extremely well-lubricated or else the motor will stall. It takes a lot of torque to open even a mildly sticking casement window.

-- Bobby G.

Robert Green wrote: I'd use the squiggly rain sensors like the one that came with my power casement window kit. They can detect single droplets of water hitting the sensor. I'll dig it out and get the specifics if the OP's still interested.

-- Bobby G. Jim Baber is very interested in what you are talking about in your "power casement window kit" you mention here. Would you please Email info about this kit to him at jim@~~~baber.org.

Then why bother?

A tipping bucket meter is the only commonly used device that I know of that "measure[s] quantity of rain in inches". A typical threshold is 0.04" or so.

These are not to be confused with the sensors sold to homeowners for controlling lawn sprinklers. These have higher thresholds and greater time lags as is appropriate for the intended application.

Agreed -- if you mean that it would probably trick you.

And what theory might that be?

Sometimes. But often/usually not at the beginning of a rain event or during a short one.

And the temperature-humidity conditions that create dew (a frequent occurrence in some locations during some times of the year) would cause a false alarm.

which would sometimes be wrong and sometimes be wrong.

Note that the HAI line of controllers (Omni etc) you hawk in this newsgroup doesn't have analog inputs for analog humidity sensors nor appropriate digital inputs for digital output humidity sensors. So you would have to have an additional external controller or circuitry to accomplish this with appropriate programming or analog computing. (Good reason to get a different controller IMO).

... Marc Marc_F_Hult

I designed/built a very simple but effective rain sensor some

35 years ago. It consisted of a piece of strip board (Vero board) with alternate tracks connected, and placed horizonally with the tracks uppermost, exposed to any rain, which would bridge the adjacent tracks and form a circuit. A separate circuit monitored for the bridging of the tracks via a simple 2 transistor amplifier driving a relay. It gave you a very early warning at the first few spots of rain, usually before you even noticed it, but no indication rate of rainfall.

Some further refinement was a slight tilting of the board so rain would run off, and glueing about 10 resistors across the underside to provide something like 1W of heat in total which prevented dew formation and helped dry off the board quickly when the rain stopped.

The final result worked perfectly for a number of years. Occasionally I had to clean off the top, although even when birds crapped on it, it still worked OK except for perhaps an initial false trigger at the time. (You could solder a few upstanding wires to the board to stop birds sitting on it.)

Neat! IC's with high input impedance have made this a bit simpler in the intervening decades. Here's a current commercial example:

Note that Andrew would appear to have the fortune of living in the British Isles where rainfall usually contains significant amounts of salt derived from the ocean, and so has significant electrical conductivity. (Conductance is the mathematical inverse of resistance.) Folks that live in the center of large continents will find that rain detection using the electrical conductance of the rain is not so easy because the concentration of dissolved solids is typically less.

'Pure' water has extremely low electrical conductance -- about 10,000 times less than sea water. Conductance is proportional to the concentration of electrolytes ('salts') in the water, so on average, it is easier to make a sensor trigger with scattered drops of rain in coastal areas than mid-continent.

There are fixes, eg: pour salty water on sensor after each heavy rain and allow to dry if the birds don't help out ;-) . However this will tend to oxidize the surface layer of the sensing conductor grid, raising its resistance -- hence the use of gold plating in commercially-made sensors.

HTH ... Marc Marc_F_Hult

Strikes me as bass ackwards overkill. Why not selectively replace a few windows with awning style crank windows, and just leave them open a crack or so when you aren't home ? Baring a torrential freakish storm, the most you may find, even in a hard windy rain, is a little dampness from some minor splashing. Perhaps you could just have a few outside awnings installed to allow you to crack your existing windows?

Your alternative, to try and automate the opening and closing of windows would be costly, would likely require frequent maintenance, and would require elaborate mechanisms, armatures, motors, and electricity. The last item BTW often gets lost in a storm of any consequence which would defeat your objective.

I have a finished attic space which must have air flow in the summer. I have a Velux roof window which is of an awing design type. I leave it partially open most every day. Occasionally, when a bad summer storm moves through and I may be at work, the worst I find is some slight amount back splashed water which I can live with. I just don't keep anything too important under the window.

I see this kind of automation question all the time. What do people do about safety? Keep the window from closing on your cat, your kid, your eyeglasses left on the sill??

I once left a can of gasoline too close to the garage door. When I closed the door, it knocked the can over. I'm REAL glad I was watching the door close. And I watch it until it's closed and the motor is off, every time.

Some things should NOT be automated. mike

Jim interjected: I have a similar problem, but rain would be a very occasional consideration, considering Fresno is to all intents and purposes a desert as we have less than 11 inches of rain annually (usually). My problem is not opening the windows while the outside temperature is greater than the air conditioned interior air, yet open the windows as much as possible to get fresh air and reduce AC costs by running my whole house fans. Unfortunately in the hottest time of the year this time when the outside is cooler than the inside occurs very late (or early in the morning) sometimes as late as 02:00 AM. I do not care to stay up until that hour just to open windows that will need to be closed again at 07:00 in the morning.

Mike there are safety devices for garage door systems on all but the cheapest systems, maybe you should either spend a little more or take a little more care.

See Mike, even you admit (by using that cheap system) any tool is a useful tool if proper care is taken.

Just because you don't get it doesn't mean he shouldn't try to find a solution. Replacing windows is not a solution for many folks. If not due to the cost but also aesthetic reasons or even building restrictions.

Besides, if people don't make use of the current solutions how do you expect better solutions to evolve? Better solutions more often grow out of learning how current ones could be improved. Following your advice nothing would develop. Not exactly progress, eh?

I guess that's my point. It's my opinion that many people don't think past the end of their nose. If they hurt their stupid selves, that's ok with me. When they risk hurting others, I get excited.

It certainly is possible to build a safe system to close your windows. I'll bet money that the OP will settle on something unsafe. I merely wanted to cause a safety thought to happen.

In college, my hippie neighbor fell asleep smoking pot and burned down his apartment...and MINE!! I'll defend his right to engage in unsafe activities...until it negatively impacts others. mike

Those pot smoking, hippy, home automators will get you every time. Most of my hippy college neighbors used roach clips which helped to prevent fires and optimized their hippiness at the same time. I'm not sure how many of them were into home automation though. Most were too busy making brownies. :^)