Author Topic: Help Moisture sensors  (Read 936 times)

Ruben

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Help Moisture sensors
« on: October 18, 2017, 10:15:10 AM »
Hello everyone

I have no specific knowledgment about electronic devices but I would like to build a device to save moiture data from gypsum sensors such as watermark several times per day.

What Moteino model is best suit for this job? What would I need apart from Moteino?
It would be in the field for a long time, what kind of battery I need and how is connected to Moteino? Is it also posible to supply Moteino through solar panel?
Must I write the "code" for everything or there are pre-made codes?

Thanks in advance!

TomWS

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Re: Help Moisture sensors
« Reply #1 on: October 18, 2017, 08:32:58 PM »
I think if you search the forum for 'moisture sensor' you will find a wealth of information.

Felix

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Re: Help Moisture sensors
« Reply #2 on: October 19, 2017, 01:10:20 PM »
Ruben,
Maybe you already have experience with gypsum moisture sensors, but just my 2 cents - I worked on a side project where the user used gypsum sensors and they didnt work that well. Maybe it saves you some trouble.

TomWS

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Re: Help Moisture sensors
« Reply #3 on: October 19, 2017, 07:00:06 PM »
Ruben,
Maybe you already have experience with gypsum moisture sensors, but just my 2 cents - I worked on a side project where the user used gypsum sensors and they didnt work that well. Maybe it saves you some trouble.
On the flip side, Watermark sensors are what I've used predominantly for the last 11 years and I find them to be the best ground moisture sensor there is.  You do have to also measure the soil temperature at the same point as the probe because you do need to compensate for this.  Most everything else is either slow, doesn't work accurately in the soil I have, or is unreliable over time.  OTOH, IF you take the measurement at the very same time of day where the soil temperature is pretty much the same day to day, you can reliably use a simple continuity tester and two non-reactive metal probes to gauge whether you need to water or not.

Tom

Felix

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Re: Help Moisture sensors
« Reply #4 on: October 19, 2017, 10:18:44 PM »
Thanks for the extra feedback, maybe others who have used them can share their experience as well. I just wanted to throw in what I heard from a 3rd party who used them in a farming application.

Ruben

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Re: Help Moisture sensors
« Reply #5 on: October 20, 2017, 10:14:21 AM »
Thanks to both

yes, we are working with watermarks sensors and we take control readings several times per week with a hand device.
I would like to save readings each hour and to graph an water potential curve and maybe to see if the tree is suffering at some point.
About the temperature I've read that affects water potential readings by 1-3% per Celsius degree. So If I want readings for 1 month I can assume 10%water potential error but If I want readings for entire campaing (1 year) I'll need a temp sensor.
My doubts come from my lack of electronic knowledgement. I suppose man has to weld, to wire and to code different pieces and make it work properly.

At this moment I have it clear I need 4 analog pins to read  the "electrical resistance" of the sensor. 1 analog pint more due to temperature sensor. Something to save or send the data (sure its not easy such as plug n play),a power supply and a code.

What dou you think is the easiest way to join these pieces for a noob?? :o

Thanks again!

Felix

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Re: Help Moisture sensors
« Reply #6 on: October 20, 2017, 03:52:18 PM »
With electronics its a little tricky and guessing doesn't always work that well.
But internet and google to the rescue, topic search will reveal troves of information and help you. And hey, that's why this forum is here, to help answer and guide in projects that involve electronic/IoT/wireless projects (and hopefully include a Moteino too :) ).

TomWS

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Re: Help Moisture sensors
« Reply #7 on: October 20, 2017, 04:30:34 PM »
For the sensor, I use a circuit I found in Appendix 1 of this document: http://www.emesystems.com/pdfs/SMX.pdf
Note that I only use the LMC555 portion of the circuit, leaving out the VR, R3 trim resistor, and the 1K current/voltage resistor R1,R3,C1, and VR.  I power this circuit from a GPIO output only during a measurement interval.
I use the frequency output into AtMega 328P pin D5 (which is routable as a counter clock pin) and use the Frequency Counter library to count the pulses.

This document also describes the temperature compensation necessary to improve the accuracy of the sensor.  For temperature probe I use a Waterproof version of the ubiquitous One Wire DS18B20.

Tom
« Last Edit: October 21, 2017, 10:02:54 AM by TomWS »