In fact, after some testing I realized that the resistance of my sensor is sometimes 450K and sometimes 2K...! I guess there is a bad contact somewhere...
@jeroen: Do you remember how much was the resistance of your sensor?
Self sustained garden
(24 posts) (6 voices)-
Posted 3 months ago #
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Here are a couple of photos: http://www.flickr.com/photos/pedro_nf/4689195414/ http://www.flickr.com/photos/pedro_nf/4689195356/ I guess the bad contact is because of the screw terminals I'm using... I'll remove them and solder the wires directly to the anodized nails.
Posted 3 months ago # -
The previous post with the correct syntax...
?!? Why the hell the photos are not visible?!?
(Because you're not linking directly to images... sir - so I've removed the !'s)
Posted 3 months ago # -
Did not remember, but I have two spare, so I tried a minute ago. Dry (it was for weeks in the livingroom with +/-50% relavitive humidity) 60 MegaOhm, Wet (after 2 minutes in a glass of water) 50 KiloOhm.
regards Jeroen
Posted 3 months ago # -
The sensor when dry behaves like an open circuit and after 5 minutes in water is at 3K ohm. I left it plugged to the JeeNode while drying out so I can have the resistance curve in time while drying out. I'll publish the results tomorrow.
Posted 3 months ago # -
Some more photos and a picture of the data collected while the sensor was drying out, after 5 minutes in water. It started out at around 3K ohm and after 22 hours it was an open circuit. I didn't measure the temperature, it is pretty hot in my small lab when I have the PC on all the time.
http://www.flickr.com/photos/pedro_nf/sets/72157624247303342/detail/Posted 2 months ago # -
Hi, I'm not sure how you measure the resistance but it is worthwhile to measure once with + on pin A and - on pin B. then do the next measurement in reverse ( - on A and + on B).
Why ? because DC corrodes metal very quickly in water. when you reverse then the chemical processes are also reversed and corrosion is a lot less.
Posted 2 months ago # -
@raalst: I measured the resistance with a multimeter for a couple of seconds. The voltage applied by the multimeter in ohm measurement is small I guess. For the normal working I'll be applying 3.3v to a resistor divider of a 10K resistor and this sensor, using a digital output, and then measure the voltage to the sensor using a ADC. Do you think in long term the metal will corrode, even if it is galvanized?
Posted 2 months ago # -
I think I re-invented the diode!!! After raalst post I tried measuring the resistance both ways, that is, exchanging the multimeter connections. Guess what? I have 22K ohm in one direction and 470K ohm in another! Thats a huge difference! How is this possible?
Posted 2 months ago # -
I measure both ways the same value. So something is wrong.
Posted 2 months ago #
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