Water me, Man!!!

today i started building the 'Water me, man!',
which is a man-figure made out of wire and componants,
that has it's feet in a plants' soil, and it's head glows when the plant needs water.

the idea is to make a plant-watering-indicator that costs very little money..
this one consists of +- 5 components : a battery, 2 resistors, 1 transistor, an LED, and wires..
which means MAX MAX MAX of 1.5$. (if every components is 1 shekel..)

it works on simplified TTL NOT gate:
\\\ if 'moisture' (current between probes) < 'threshold' (set by resistors' values)
\\\ then LED=glow.

the sketches + schematics!:

the alien in position:

i will build it again, with a new battery (this one is already finished from all the games..), and capsulate it in an transparent capsule - open-source proper. then it really will look more HUMAN.


Daniel said...

So... Does it work?

In addition, how long does the battery last?

Anonymous said...

would it be possible to use a potato to power the led?

Mr. Biggs said...

Hey, Cap'n.

I ain't too keen on the idea of electrocuting my begonia roots. It just seems cruel.

But I can get past that-

IF you revise the circuit to ditch the LED, and replace it with a digital flash audio player at plays a loud,looped, tinny scream of agony.

THAT would make a million dollars.

I'd buy five.


2707 Jackson Drive said...

I am trying to read your handwriting on schematics to get a parts list. Is this what I need:
3 VDC Battery
2N2222 transistor
390 resistor
1k resistor

Any specs on the LED I need to look for?
Also, what should I change out if I wanted drier or wetter soil conditions (or possibly something I can set for each individual one I make, I have a ton of plants)? I have a small amount of experience otherwise I probably wouldn't need to ask.


Dave said...

Nice!! Simple elegance...

One suggestion that would greatly extend battery life:
Can you use one of the flashing LEDs, with the built-in timing and charge storage cap?

Mike said...

I should be able to tweak this to work on a pets water dish, right?
I want an audible signal rather than a light though. What would I need to change?

Great idea!

AppsByAaron said...

How does the electric current through the soil effect the plant? or does it ?

Dave said...

Just took a closer look at your schematics. The transistor diagram is drawn correctly, but you have the emitter and collector labels swapped.

Anonymous said...

About how long would you say the battery lasts?

Humanity said...


Cool idea,

I cannot read out the values of resistors and others, can you please add that too.

Keep inventing buddy.

Wish you luck

alex said...

that is awesome!
how do I make one for my orchids?

jeffm said...

Great concept. Love the idea of a dirt-cheap, dirt-sensing circuit. As someone who could can plead guilty to involuntary plant-slaughter, I can see the utility.

Unfortunately, the circuit as drawn is going to consume a little over 7mA in the idle "off" state, which is bound to be a battery-killer. Dead battery could mean dead plant. Consider using a p-channel MOSFET with a multi-megaohm pull-down resistor. That will take close to zero current (pA) when off and still keep the part count very low. You'll have to pay a little more for the MOSFET than the 2N2222, but what's the cost of a new plant nowadays?

Thomas said...

Very nice! But is it just me, or is this circuit eating battery even though the LED is not on? (with probes directly connected to each other)

Anonymous said...

I wonder if it worked?
you should have an idea of various parameters, like the min-max value of soil moisture wanted and the like. and will it work efficiently with smaller changes of moisture?


ori berger said...

looks useful to many plants have died under my un-watering hands

biojae said...

I have built this, but my only concern is that one of the electrodes is being eaten by the electrical charge

Anonymous said...

So how long does a batter last?

Justin said...

I built a couple of these using parts I had lying around, and the batteries died overnight.

I did swap the 2n2222 for 3904, that might have something to do with it but I don't know for sure what the difference is in these two transistors and I'm way too lazy to look it up. ;) I do want to try it with a mosfet as jeffm suggested.

awesome, simple circuit, Nur! thanks for sharing.

Seb said...

Mine is working for a couple of days now on a brand new battery. (I'm using an 2N1711 instead of the 2N2222)

To bad the soil has to be really dry for the LED to light.

If anyone has a schematic with a mosfet I'd definitely try building it.

Then if it drains to much power still I'm hooking it to 2 AA rechargeable batteries.

Vexillum Silentus said...

Has anyone tried this with the p-channel mosfet with the pull down resistor? If so could you post a new diagram? I've been trying to figure out where the pull down would go for like 3 weeks now. I'm just beginning electronic engineering.

Anonymous said...

Saw lots of traffic on this when the circuit first got posted but then nothing since then.

Hoping to bump this back up as there are a couple of questions that need to get answered.

1) what components should you change if you want to vary the moisture level in your plant? (ie. a drier or wetter soil)

2) Anyone had a chance to do the p-channel mosfet?

I am brand new to electronics and am learning what each piece does - but I am pretty much at a "follow the recipe stage"


Nur said...

hey anonymous T!
thanks for the post.

and straight to the answers:
1. in order to change the moisture threshold - try playing with the values of the PROBE resistor
(DO NOT TOUCH THE 390ohm resistor on the transistor's emitter)
i advise using a Solderless Breadboard - it's good for that.
and beware of the transistor - it can get REALLY hot (i got a round scare on my finger for a few days while experimenting what you are about to do exatactly...hehe)
2. i didn't get to try this on my own :\

good luck on learning electronics!! i'm not much of an expert, but i learned only for about a month on my own - from PDFs and WIKIPEDIA.. and some other sites.
if you MAKE something interesting - feel free to link from my blog or email me!


top soil said...

but is there any way to track result on a long term basis? will the batteries last?

IBM Lenovo Laptop Batteries said...

This is so great.
Im so bad at knowing when to water my plans. I love them, i do. Im just so bad with it!

I'll definitely give this a go! i have a few plans around the house and a few in the balcony. How long will the battery last you think?

Thanks again, this is great.

Tony I said...

It would seem that changing (the undefined) distance between the two probe ends would change the point at which the signal would light the lamp, thereby one could expect that all one would have to do is timed experiments with plants that are expendable to arrive at a probe to probe distance giving the moisture level you prefer to maintain in a given plants soil.
Perhaps not. But I'll try it.

ayshwarya rajagopalan said...

i wanted to know the use of the various components used here
1.390 ohm resistance
2.1K resistance
i also wanted to know which of the 2 resistance acts a sensor??

i tried this today and was wondering about the functionality of the components being used..

louis said...

I think its a pretty good idea not that there aren't other sites out there that already do something similar but I think it might catch on here pretty well.