Wetness sensor for server rooms

Other Hardware Sensors
1

Hi all,

I've been searching quite a while for a wetness sensor that is suitable to detect the presence of water in places like server room floors.

I have used this probe a few years ago: http://estore.sensatronics.com/index.php?l=product_detail&p=16

It's very good, but also very expensive (just the probe is expensive, plus the EM1 unit that reads it).

I'm looking to put together a simple solution with arduino. I already have temperature and humidity going, but I'd like to add the wetness sensor to it.

The requirement is to have a strip that detects presence of water, anywhere along the sensor.

I've bought some of these: http://dx.com/p/062301-water-sensor-working-with-official-arduino-products-red-228292, and they work, but I really need a longer sensor.

Any idea if anything like this exists for arduino?

2

Well maybe a low tech approach would work.
Just run two bare wires, with some cloth insulator between them. As long as you want it to be. When the cloth gets wet, there will be a resistance on the two wires.
Not high tech, not pretty, but it will work.

3

Hi Jack,

Thanks for the reply.

I think the high-end probe that I linked to is actually essencially what you describe, just in a polished format. Which begs the question why it's so expensive.

I'm interested in giving the low-tech approach a go. I'm fairly novice to electronics, so I'd like to know if I should approach the reading of the resistance by following the method described in this thread: http://forum.arduino.cc/index.php/topic,21614.0.html
Or is there a better way?

4

http://www.ebay.com.au/itm/DC-12V-Rain-water-sensor-module-Relay-Control-Module-for-Arduino-robot-kit-/261264861586?pt=LH_DefaultDomain_0&hash=item3cd4996992

Basically the same thing, but a variant on it...

But yes, 2 wires would do well, a hygrometer? well a Barometer sensor eg

http://www.ebay.com.au/itm/DHT11-Digital-Temperature-Humidity-Sensor-Moudle-Probe-For-HVAC-Arduino-4-pins-/300882572324?pt=AU_Decor_Furnishing&hash=item460dffb424

that one..... Could be used to detect a significant amount of moisture to indicate water / flood

5

If using bare wires in the cloth like jack suggested, use stainless steel wire like for electric fences, so it don't corrode.

6

Instead of checking for resistance, you might take a spring clothespin apart, and drill out the jaws to mount a couple of small brass bolts on each jaw. Wrap your wires around the bolt, and tighten down with a nut. Re-assembled the clothespin; when the jaws are closed, the "switch" is closed and current can run through the wires (wire one side to ground, the other to a digital pin, set the internal pull-up and monitor).

Put an uncoated aspirin tablet between the jaws (so the contacts don't close), and set it on the floor, with the edge the aspirin touching the floor. When the floor gets wet, the aspirin will soak it up, fall apart, and the jaws close, making contact.

This kind of "sensor" was described in one of the many "Engineer's Mini-Notebooks" written by Forrest M. Mims, III (http://www.forrestmims.org/), but I believe it predates that publication by likely decades (I'm sure I saw something like it in an old Popular Science magazine from the 1940s or earlier).

7

Thanks everyone.

I never imagined this could be so easy! :slight_smile:

Just did a quick test with a couple of stripped jumper cables, and using the schematic and sketch on that resistance reading thread and it's extremely sensitive to any trace of water along the cable pair. Now just need to find good cable (stainless steel like elac suggested) and I'm good to go.

Again thanks everyone for the great tips!