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simple rain sensor


yesyes

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Today I have been experimenting a bit with a a simple rain sensor.

I just took a spare piece of strip board PCB and connected every other strip to one wire and the ones in between to another.

Then I connected it to a multi meter and measured the resistance (at the 2Mohm setting).

Then I took a bit of tap water put a few drops on the board. The resistance dropped considerably (as expected).

This is just an experimental prototype but I'm hoping I'll be able to connect that to an Arduino at some point.

I found it rather hard to dry it up again though. Resistance didn't want to go up to over 2Mohm again. When trying to blow it dry with my mouth resistance actually dropped. I think it needs to be heated from underneath to be reliable, so that the water evaporates when it has stopped raining.

Attached the pictures of the "sensor" and here's a short video of the experiment:

post-14790-133877493529_thumb.jpg

post-14790-133877493535_thumb.jpg

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Yes, I was wondering about the copper. Even fingerprints turn rather dark after a short while. You think tin is more resilient?

I was thinking of some NiChrome wire under the board to heat it..

How did you work out the resistance values for triggering a rain alarm? Or do you consider everything that's not "open" as rain?

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Hmmm, that looks good. If it wasn't for the relatively high postage cost.

Also, I wonder how big it is. Judging from the holes for the wires it's a bit on the small side. Might need a few in parallel. But gold strips sounds ideal...

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Basically yes.. all I did was use it to switch a transistor that drove a buzzer and a relay

Would you mind sharing the circuit diagram for that, please. I'm having some kind of blockage here... It's been a fair few years since I have "developed" my own circuits. ;-))

Did you just use the sensor to connect the Base to ground (assuming a PNP transistor)? As far as I can tell the sensor can have a resistance range of 0 ohm to several Mohm (or even infinite if it's really dry).

I guess the sensor with another smaller resistor in series (to protect the transistor in case the sensor is shorted accidentally) connected to the base on one side and ground on the other side should be OK but I'd like to see how you've done it, if you don't mind... ;-))

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OK Found it...

one end of the sensor was connected to 5V the other end to a 1k5 resistor which went to the base of the 2N5551 (NPN) Transistor a 10K resistor was fitted between the base and emitter and the emitter connected to 0V.. the Relay was the collector load... (Flywheel diode across the coil optional) ...

The relay was a Finder 38.11.9.005.4001 5V 10A SPCO

Peter...

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Yeah, me too usually. Especially for this circuit the actual resistor values are not too critical. But I've recently got one of these 1000 resistor kits with some standard values as it looks like I've re-discovered that old hobby of mine .. ;-)

Didn't have too much lying around any more after almost 20 years and moving to a different country... ;-)

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hehehe, nice one... I especially like the use example on Maplin's website:

"Simple to construct and great if you get bored watching the bath fill!"

You wouldn't have a lot of time to stop the water before the whole unit is submerged and silenced... ;-)

Thanks for the link, Kevin, but I think this is something I rather build myself (more for the satisfaction than saving money in this particular case). But it might be interesting for others....

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