Office plant monitoring

[Lars65]

Hi!
At the moment do I only have three sensors, and I will be using them on the same arduino. Those will be powered by wall power.
But I have ordered some more sensors, and some of them will be battery powered.
Though both me and my wife often forget to water our plants, do I really like this.
I use Domoticz, and it's easy to get a notification when it's time to water.
You have been really helpfull. Tomorrow will I mill a new PCB, to test this code.
:)

[damien]

Hi @mfalkvidd and thank you for your nice work and sketch.
I just have one question about the power pin, I saw on datasheet that the adruino pro mini can handle 40mA max per powerpin. I Have four of these soil moisture sensors but cant find how much current they need... they use a LM393, and the datasheet say 0.4mA..
Did you think than i coul plug all of them on the same powerpin or i need to use your second sketch ?
Thanks in advance !

[mfalkvidd]

@damien: I don't know, unfortunately. Maybe @Lars65 can do a measurement on his moisture sensors?

[damien]

@mfalkvidd Ok thanks for your reply, i will wait for @Lars65 to see if he has done the measurement, else i will do it by myself on mine when i receive them.
Thx

[Lars65]

Hi Guys!
No I haven't made any measurements.

{ 4, 0, 1, // This assumes 2 sensors per pin. First two sensors are powered through pin 4, using analog pins 0 and 1
**5, 2, 3, **// Second two sensors get power from pin 5 and are connected to analog pins 2 and 3
6, 4, 5 // Third set of sensors get power from pin 6 and are connected to analog pins 4 and 5
}
So I did change 4,0,1, to 4,0,. What I saw with this was that I use power pin 4, to the analog input A0. So now have I made it so A0, has powerpin 4, A1 has powerpin 5, and A2 has powerpin 6.

[mfalkvidd]

How did thinks go @Lars65 ?

I thought a bit more about this problem and I think I have come up with a pretty neat solution:
Throw away the chip on the moisture sensor and connect the "pitchfork" directly to the Arduino. Connect one prong to GND and one prong to an analog pin. No power pins are required.
https://codebender.cc/sketch:177182
The chip on the moisture sensor is basically a voltage divider. We get the same thing if we use the internal pull-up resistor on the Atmega processor.
EDIT: This means you can buy just the "pitchforks" really cheap: http://www.aliexpress.com/item/10pcs-Soil-Hygrometer-Detection-Module-Soil-Moisture-Sensor-Probes/2051713873.html

[Nicklas Starkel]

@mfalkvidd , I think there has been many discussions on how these sensors corrodes over time.
I can see that this node sleeps between the readings and thus reduces corrosion as it only is powered during reading.
However, some threads I've read suggests that you alternate the power, as well, between readings.
Something you might implement in the code?
Also, do you have an estimate on the duration usage on the batteries for one of your plants?
Cheers!

[mfalkvidd]

@Nicklas-Starkel If a measurement is taken once per hour, the sensor will only have power 0,008% of the time.
If corrosion still is a problem, and if the corrosion can be avoided by reversing polarity for every second measurement, I might add it. It would add complexity to the sketch though, and complexity is often the enemy of reliability.

Also, for people wanting to use multiple sensors on the same mcu, reversing polarity would cut the possible number of connected moisture sensors in half since it would require two analog pins per sensor.

My estimated battery time on 2xAA for a Mini Pro with removed power led and voltage regulator is 1-2 years.

[damien]

@mfalkvidd said:

How did thinks go @Lars65 ?

I thought a bit more about this problem and I think I have come up with a pretty neat solution:
Throw away the chip on the moisture sensor and connect the "pitchfork" directly to the Arduino. Connect one prong to GND and one prong to an analog pin. No power pins are required.
https://codebender.cc/sketch:177182
The chip on the moisture sensor is basically a voltage divider. We get the same thing if we use the internal pull-up resistor on the Atmega processor.

Hi @mfalkvidd and thank you very very much for your new version of the skecth for moisture sensors, its very clever ! i will test it as soon as possible

[mfalkvidd]

@Nicklas-Starkel last weekend one of my sensors broke. Both pins were completely corroded and broke just where I connect the dupont wires. I think I will use hot glue to protect the connectors, but I have also added alternating power to my single-sensor sketch. I have this sketch running on three sensors now.
https://codebender.cc/sketch:158460

[memheli]

Newbie to controllers. I'd been looking at PanStamp for this project, and came across your post from Google. This would be my first project w/ micro controllers. How is this tied to the internet for reporting?

[mfalkvidd]

In MySensors lingo, the Arduino is called a sensor. The part that MySensors calls a controller runs on a "real" computer, and gets information from the sensors. The controller usually handles reporting. The documentation at http://www.mysensors.org/about/network can probably give you a good overview.

[m26872]

Just some ideas to the corrosion issue (any photos?). If both pins were corroded, it may not be sufficient with polarity switching. Perhaps a simple active cathodic protection system could help. E.g. a +wire limited to a few uA and wrapped with some aluminium foil in the soil near the sensor?

I haven't yet got to it, but the plant monitoring is on pretty high on my list.

[mfalkvidd]

@m26872 said:

(any photos?)

[rajbadri]

@mfalkvidd
i am using your sketch for indoor plant monitoring but have modified the sleep time to one hour . the problem i am facing is that every alternate humidity reading i get is a 0
like
first reading ------ 67%
second reading ----- 0%
third reading ------65%
fourth reading ------- 0%

and likewise

Please Guide

Thanks

[mfalkvidd]

@rajbadri which pins are your sensor connected to?

[doblanch]

Hello,

I'm on the same project personally...I using 2 battery... this part should work between 3.3 V and 5V...
finally with 2XAA we only have 3V, and the max value for me is 750 not 1023... did you get 1023 when into the water?
I use a gold plated sensor, and the plug will be into a seal to avoid corrosion and water to go in.
I use a sensbender where I connected on A3 the pin use for the soil moisture sensor.
Could you confirm that change the polarity help to avoid corrosion ???
thanks

[mfalkvidd]

@doblanch said:

Could you confirm that change the polarity help to avoid corrosion ???
thanks

No I can not. All my sensors change the polarity, so I can't tell if there is a difference. You'll have to experiment.

[mfalkvidd]

@doblanch said:

the max value for me is 750 not 1023... did you get 1023 when into the water?

I haven't tried in water. I don't care about the absolute value, I just note the reading when the plant needs watering and set a notification for that level. One of my plants needs water at about 70%, another at about 5%. It will vary wildly between different plant types, climate and soil composition.

The value for water will probably vary as well, depending on the water. Distilled water, rain water, tap water, salt water will all have different resistance.

And the value will vary depending on temperature and different Arduinos since the pull-up resistor is inexact.

[doblanch]

@mfalkvidd ok ; thanks I willl try :-)