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Topic: Moisture Sensing with 555 (Read 7606 times) previous topic - next topic


Nov 13, 2010, 07:02 pm Last Edit: Nov 13, 2010, 07:03 pm by xxlbreed Reason: 1
I know this has been discussed on multiple occasions however I am looking for the
BEST AND SIMPLEST circuit diagram that will let me measure soil moisture with a 555 timer and a diagram of a diy sensor unit that you like best.
Just post me a bunch of schematics. THANKS!

what ive got so far:


remember .. easiest and best .. ;)


yes thats what i figured too..

best is works best for how simple it is. I do want a 555 in there. any help would be appreciated..



I question your obsession with 555?  It is a handy chip, but if you are using Arduino, it seems to violate your requirement for "easiest".

I need this to work for a couple of years... ac current measurements will be more reliable for longer than dc causing electrolysis...


This page had a pretty good explanation of why they make sensors out of plaster. And a quite straightforward construction tutorial.

fantastic, i like it!

PS: You might want to re-consider your avatar. Using the same one that is already used by several other people is confusing.

working on it.. photo shop is on its way to my house.. bear with me.

555, any circuit diagrams, anyone?


I see, do you think you could write a code example I can work with?

how would the circuit look? same as for say an ldr?


I would like to use the tone() function, is there a specific frequency you recommend?

The thing I cannot wrap my mind around on ac is that when id use dc im measuring the resistance. What am i measuring when using ac? Am i still measuring resistance? I never quite understood that part..

Very helpful. THX!!

ps.. how do you become a godmember?/user


Very smart ideas and good opinions with a great sense of humor - why are you not president?  ::)


To use alternating DC, simply connect each side of the sensor to an Arduino digital pin and an Arduino analog in pin. Then you can ground one pin and pull the other up and make a voltage reading. Alternating pins on the next reading, etc.

i tried to visualize this .. not happening.
are you saying I should use up 4 pins per probe? 2 dig, 2 analog ? Im more of a visual guy .. sorry  :-[


Nov 14, 2010, 03:25 am Last Edit: Nov 14, 2010, 03:26 am by xxlbreed Reason: 1
okay that gives me some more to work with :D

I heard that plaster of paris gets soft after it is exposed to a moist area for a while. Most say that concrete and just sand in a fine wire mesh work best...So what i did is go to the roadside, take a sandbag that has been lying there all by its self for months and cut it open. I took 1part sand, 2 part plaster of paris and 1 part cold water. mixed it up and filled it in a pvc tube with 2 galvanized nails that i kept apart with a 22awg wire insulation...
after 10 min they are rock solid but im gonna leave em in the tube for another couple of hours before cutting them out...
updates to follow ;)

time to study some math and physics... :-X

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