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HomeMade Soil moisture meter / Automatic water

Discussion in 'General Marijuana Growing' started by rolln1up, Jan 17, 2008.


    rolln1up Well-Known Member


    Heres a circuit I built for monitoring soil moisture. Its simple to build and lights an LED when the soil becomes dry and its fully adjustable to individual standards. I was able to build mine and place the entire circuit inside of a pin and I am using it in my living room on my San Pedro cactus. THis circuit has a lot of potential because of its small current draw and could easily be modified to water plants outside automatically when soil becomes dry. No more packing in water or worrying about out door plants. Any thoughts?

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    KingOfBud Well-Known Member

    We used to make these things in tech class. Our circuits were abit more complicated. We had 9v output leads, so we could trigger watering. Nice nonetheless, any pics of the finished product?

    rolln1up Well-Known Member

    No i don't have a pic of it yet. Yes I could have improved the circuit by using an op amp and measuring the reactance of the soil and produced a more accurate meter, but my goal was to make a simple reliable meter that I can use on my outside plants to automatically water them and if they get busted Iossing the meter isn't a big deal. Simple to construct was another major design factor as I will probable be building at least 30 for outside. Thanks for looking oh and I'll try to get a pic of my meter up shortly

    rolln1up Well-Known Member

    any suggestion on how to make a cost effective water vavle

    cyborgasm Well-Known Member

    Very nice! Simple, small, elegant

    I'm curious how long the battery would last. I'm a beginner when it comes to circuit analysis, so I don't know exactly how to deal with the transistor. Do you know how many amps the circuit draws when the plant is wet? Dry? (picking a reasonable resistance for the LED)

    Capita Well-Known Member

    watching this thread

    blonddie07 Well-Known Member

    this is nice! :) easy to get stuff too...

    rolln1up Well-Known Member

    The circuit pulls about 9 mA so the led doesn't get really bright but it is very noticable. (actually I believe it is pulling 6.3 mA as you will have 2v across the LED and .7v across the transistor leaving 6.3v across the resistor which should give a current of 6.3mA a little low for an led so using a smaller resistor wouldn't hurt.). Ive been using this simple circuit for awhile now and that batter still has plenty of juice an led can go for quite some time on a 9v battery.

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