Soil moisture monitoring

[ChrisCragg]

Before I came across OpenSprinkler, I had anticipated creating my own Arduino based controller. One of the features that I thought was important was to test the soil moisture before running a program. I bought a couple and it looks like they would be easy to implement. I happen to have 2 unused wires in my sprinkler harness and intended to use 2 of the analog GPIO pins to check the moisture. It was going to follow this logic:

When you get ready to run a program, check the soil moisture. If it is above N1%, don’t run. If it is between N1% and N2%, run half the time. If it is below N2% then run full.

I was going to tie each station to one of the moisture sensors. That lets different parts of the yard get different run times.

A future upgrade would be to somehow put the moisture sensor in the same area as the solenoid (assuming it is close to the region watered), then send moisture condition back over that same wire (would require some sort of multiplexing in the field)).

Thoughts?

[Ray]

I have not planned to add soil moisture monitoring to OpenSprinkler yet. This is mainly because I suspect most users still prefer a time-based program, with potentially some weather-based refinement. Adding soil moisture sensor will potentially complicate the scheduling, and in case the sensor fails to return correct reading it can be come a source of reliability issues.

I do have an upcoming product called OpenSprinkler Sip, which is designed for indoor plant watering and it does use a soil moisture sensor. You can take a look at the picture on this webpage:
http://rayshobby.net/

[ChrisCragg]

I think we (the community) will want this in the future. I agree that it is a bit complicated, but I don’t think it’s terrible.

[dneveceral]

It would be perfect, if I could connect not only 8 valves but 8 moisture sensors too. Then I could setup watering for valve no.1 at monday from 4:00 AM (but only if in section 1 is soil moisture under 100), to 6:00 AM (but only if soil moisture 300 will not be reached sooner).

It is very simply and eco friendly saving of water.

Please, could you think about it? Moisture sensors are very cheap now and you can do only expansion sensor board, something like for valves.

[mike]

Newbie here. Looking for an irrigation solution for a polytunnel. Prefer zonal moisture sensors to open/close valves on a manifold supplying soaker or drip line. Water powered by gravity feed from the tank. Your soil moisture monitoring looks like it could meet my needs. Any progress on the project?

[polygnwnd]

Could hack the Toro Xtra Smart Wireless Soil Sensor. It uses the Atmel AT86RF212 900MHz RF chip and costs $45 on eBay (including receiver that contains a PIC and a relay so it can act as a rain sensor for a traditional irrigation controller).

[mike]

@polygnwnd wrote:

Could hack the Toro Xtra Smart Wireless Soil Sensor. It uses the Atmel AT86RF212 900MHz RF chip and costs $45 on eBay (including receiver that contains a PIC and a relay so it can act as a rain sensor for a traditional irrigation controller).

thanks for your input. I’d need one of these sensors for each zone which could quickly become expensive. There are cheaper moisture meters for maybe £2 or £3 each but as a total novice to coding / programming wouldn’t know where to start. Others have found solutions by using moisture sensors to accept or cancel a command sent by a timer. If the command isn’t cancelled (ie when the moisture content is below a low threshold), the timer activates a solenoid valve and irrigation commences.

I’m also looking for ways to automate the raising and lowering of a ventilation curtain – triggered by temp sensors. Maybe I’m trying to sprint before learning how to crawl!

[polygnwnd]

If your watering zones dry out proportionately then you can get by with one sensor– this would be the case for an outdoor lawn (full sun areas will be dry before shaded areas, but the relationship between the areas is roughly constant). Probably works well enough for lawns, but a greenhouse with plants at different stages of growth might need more detailed monitoring.

@mike wrote:

There are cheaper moisture meters for maybe £2 or £3 each

My understanding is that there are a few ways to do this. The resistive sensors that are most popular for DIY tend to degrade and/or malfunction over time but are really easy to build (two nails/conductors, and perhaps some gypsum for encapsulation) and simple to understand. I suspect the commercial Toro unit above and 3+6″ commercial versions seen at golf courses use this method (with stainless steel conductors).

The capacitive approach is probably longer-lived, but slightly harder to manufacture. I wonder about the longevity of FR4 PCBs in wet soil, but am curious enough that I might make one and see how it does.

Adafruit is selling a normal atmospheric (air) sensor PCB in some sort of metal housing as a hobbyist soil sensor that looks like a microphone. I wonder if it works/lasts (if it did work/last, why wouldn’t everyone in the industry be burying cheap atmospheric sensor ICs?)

@mike wrote:

Others have found solutions by using moisture sensors to accept or cancel a command sent by a timer. If the command isn’t cancelled (ie when the moisture content is below a low threshold), the timer activates a solenoid valve and irrigation commences.

That’s what the Toro unit does with its relay, it effectively disconnects the zones or actuates the rain sensor input (normally open or normally closed are both supported)

I think there are some interesting demand-driven/wireless sensor-based watering solutions that are now do-able for hobbyist/DIY. The real question is how much savings there is to be found compared to schedule based solutions (and variations: schedule+rain/freeze sensor and schedule+weather forecast) that already manage to deliver enough water. If installed base is a guide, then golf courses (big lawns) are more efficient with sensors. Don’t know much about greenhouses.

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