Test Tools: Plant Soil Moisture Monitor





Introduction: Test Tools: Plant Soil Moisture Monitor

About: I am, most definitely older than 00010101 and to put it simply, still curious about nearly everything :-) I then tend to read and/or experiment in those areas - when I have the time.. . My two "specialty...

I am going to start with a simple moisture meter one can carry about and test all their plant soils with, rather have one committed to one plant and needing one for each plant, as I had originally planned.

Insert the probe into the soil, push the button and it gives a go / no go signal whether the soil is damp enough or not.

Step 1: Parts


IC1: 4001 CMOS 2 input quad NOR gate (14 pins)
D1: Red LED
D2: Green LED
R1: 22 K resistor
R2, R3: 200 ohm resistor
R4: 100 ohm resistor
R5: 200 K trimmer resistor

One 14 pin IC socket

Misc: copper or copper clad probe, 9v battery connector, 6 lengths of insulated wire, and a pc board, box (I used an empty SwingLine staple box).

NOTE: IF you use a section of copper for the probe rather then a copper CLAD board, you will need 2 of them, and a bit of insulation attached in between the two pieces.

Step 2: Assembly

I normally try to eyeball just where components will be on the pc board, and place the Socket in what I feel is the best position for it. Everything else can be soldered into place in the order most convenient for each person.

One caution: When inserting the IC into the socket, care must be taken not to bend any of the pins or misalign them. It is easy to put a 555 into a socket, since there are only 4 pins to a side, but with a 14 pin IC, there are 7 on each side and it can be a little more tricky.

Step 3: Completion

Once soldered into place, on can cut the holes needed for the LEDs and the push button switch into the top of the case, and install.

In this case, I am able to house the 9 v battery on the inside.

Step 4: Adjusting and Testing

Once everything is ready; put the battery clip on a battery, insert the probe into soil that is of the proper moisture content; and press the button. If the red light comes on, adjust the trimmer pot. until you get a green. Then do the same for one that is not quite the proper moisture.

I few times around with get it just where you want it. Red LED for too dry, and Green for enough.

EDIT: Once I housed everything into the box, I found it was hard to get to the adjustment trimmer, so I bored a hole in the end of the device, as a small access hole as shown in the last picture. The trimmer has a slot for using a small screwdriver or similar tool on. Extra Note: on projects that have inductive sensitivity, one normally would not use a metal screwdriver for adjustment, but rather a plastic or nylon tool.

Since I made this a simple project, I did not build in any hysteresis, so adjustment to the proper moisture level is imperative.

The tester should be used before watering, since the plants roots, most likely will be in the bottom 2/3's of the soil. Press the probe in as far as you can without burying the contacts (unless you have waterproofed them with hot glue or something) before pressing the button. It is imperative that you get to that level if possible, and to always measure from the same level each time.

Watering tips can be found on line at places like this link to watering different types of plants.

Eventually, the probe will tarnish some, and the conductivity will not be as good, thus lowering sensitivity. This will make the monitor inaccurate.

You have two choices then: using a product like tarn-x to convert the tarnish back to the original metal (copper cleaner is OUT of the question as you only have a very thin layer to start with), but then you mush make sure the probe is SUPER cleaned afterward. Tarn-x and similar products are highly toxic to humans, pet, and plants.

OR you can replace the probe.



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    Thanks, and yeah, I am thinking about putting a printed label on it for that final touch :-)

    . We seem to have the same opinion of tools: As long as it works, who cares what it looks like. :)

    :-) Well, that was one reason for not spending a LOT of time looking for a box for the polarity tester. I have one that emits sound too (so you don't have to take your eyes off your work). I would have to dissect it and reverse engineer it, since I no longer have the schematic for it. The soil moisture tester requires adjusting, depending on the type of plant and the amount of dampness the soil is supposed to have. So, it works after a bit of tweaking. Do you think I should explain that it more detail?

    > requires adjusting, depending on the type of plant ... Do you think I should explain that it more detail?
    . Since this is in Home, then yes. You don't need a lot of detail. A few links to pages that will help the user determine the proper moisture. Point out that repeatable insertion depth is important. Will need to be re-calibrated as probe corrodes.

    Ok, thanks. I have touched it up a bit. Mostly in the last step.

    Sweet! Another project from Goodhart! This is great because I'm trying to grow a baby pine tree right now.

    1 reply

    Thanks. Ok, just make sure you look up what it needs as for water, and then adjust the tester to optimal conditions.

    That's cool. You've been a busy maker lately ;-).

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    Thank you, I have been trying :-)
    The last 3 days I have been a bit ill; not feeling real badly, but contagious nonetheless; so I have been confined to my quarters and well, that made for some MAKE time :-)

    That's the best kind of sickness--nobody wants to be around you, but you feel well enough to "play..."

    Yep, and, for once, I had the materials with me TO play :-)

    Excellent work! i did not realise it was going to come out so soon. And.. Nice Box!! see how much a difference a box can make??

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    Thanks, yes, we used the last staples from that box just as I finished making the moisture detector.....and no, I didn't secretly staple the parts together LOL