Garduino: Gardening + Arduino

Step 4 Build Your Moisture Sensor

Your moisture sensor consists of galvanized nails some distance apart from each other in the same milk jug of soil. When the soil is more moist, the sensor will report a lower resistance.

Solder a wire to the head of each nail, and be generous: this will be a structural connection as well as electrical. One nail wire gets connected to +5v on the Arduino, and the other goes to both an analog input and a resistor (then ground)

Comments

[ReagenWard]

How's it working over time?  Almost everyone tries nails first, then moves to gypsum or the like, and if they want accuracy, they end up with a tensiometer.

Also, DC is known to be a problem for moisture sensors over time - have you considered AC or are you just replacing your probes often?

[diy_bloke]

As a matter of fact, I tried gypsum first and then went to bare spikes. Gypsum is a bother and the sensors actually fall apart quite soon. Also they are slow in reacting.

With regard to the DC. I have not seen any problems yet with my spikes that have been in the ground for a year., but what you could do is provide the positive feed to yr spikes from an arduino pin and only switch that on right before you measure and then off again ofcourse

[liseman]

Hi ReagenWard,

I'd recommend checking all components of the system every ~month, or if you notice anything odd.  Using galvanized nails seems to help things and, if you really want to play it safer, you can modify the code to only set the pin to the moisture sensors high when you're reading the moisture value.

Hope this helps,
Luke

[typomaniac]

sounds like a good idea. Do you have an idea how to modify the code to achieve this? I am not very experience with arduino yet..

thank you so much!
tm

[diy_bloke]

Have a look here on how to write such a code: http://arduinodiy.wordpress.com/2012/04/29/garduino-an-arduino-sort-of-for-your-garden/ if you haven't already found out how to do that

[ReagenWard]

Good advice.  Thanks!

[diy_bloke]

I have used galvanized nails for some time now and they do well. In order to combat oxydation one could feed them with AC (=getting the voltages from two digital pins that you alternately switch from high to low), but I found it easier to just switch off the voltage to the pins and only switch it on when I am doing a reading.

I have these pins in the ground for a year now and they still look fine. Since winter is coming, I took them out, gave them a quick clean with a brillo. They will go back in the soil in the spring.

If they really look bad, I will just replace them

[FredicvsMaximvs]

Just curious, why galvanized? Why not stainless steel? Is there something in the chemistry that makes this work better?

[Glider-diver]

Ever try soldering to stainless steel? :-)

[Super_Nerd]

galvonized is coated with zinc so the metal doesnt oxidize

I belive there is no difference with stainless steel except it is an alloy not an electro-plating

there probably is no difference but price

[typomaniac]

hey : ) is there a special reason why you chose a 10 k resistor? what would happen if i take a higher or lower resistor?

thank you!

tm

[KarateLover21]

Nice! I just built a moisture sensor. I may make a variation of your garduino project. I love the concept of making robotic enviorments, not just automatons! This way, it can be like a garden that cares for itself! Talk about heterotrophic!

[daufhammer]

 How did you calibrate the sensors in the code.... was it just trial and error? i.e. how did you find out what the right value that the sensor returned that corresponded to the appropriate dryness that meant it was time to water again?

[daufhammer]

 sorry, just realized you totally explained this in a later step! Great project im hoping to start my own garduino project soon!

[action_owl]

cool, I had been wondering how to read the moisture level of soil definitely gonna try this out