Solar powered flowerbed irrigation controller

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1

I'll start off by saying that I'm a software guy, so I'm sure there's plenty I'm doing wrong here (and I appreciate the pointers).

I live in the city, and the only garden access I have is a 6' x 1' flower bed I built on my roof deck. Watering is a pain, so I put together a controller that waters only when necessary. At first, I tried to put together a resistive moisture sensor, using galvanized nails and an h-bridge to flip polarity and stave off corrosion. That lasted an entire week, and then was utterly eaten by oxidation (it was pretty neat seeing a 4" of a 6" nail disappear over the course of a week). Then, I shelled out $30 on a Vegetronix capacitive sensor. That, coupled with a latching solenoid (important!) and a SparkFun Arduino Pro Micro resulted in the attached. I'm still running tests, but in the worst case scenario (with the solenoid being actuated as often as the code will allow it), the battery recharges quickly enough to last indefinitely. While sleeping, this setup draws ~3mA + the quiescent current of the power controller (which is another mA or so). The solenoid I use draws about 300mA for the switching pulse.

The full BOM (aside from passives):

The source code and eagle files are available here:

The main issue I'm currently aware of in the design is that I'm using the arduino's output pins to push a 6V signal down to ground, which is about a half volt above it's maximum rating (this is on the P-channel side of the half-bridge). The right thing to do would be to use a BJT per P-channel (there's two of them) instead, but it seems to be working for now (YMMV).

Other input/advice is greatly appreciated.

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2

Without sounding anti-arduinoist i built a similar system that does not require a battery or an Arduino :roll_eyes:
I simply connected a small 12v 100watt panel to a 3a step down converter (with auto shut off) directly to a bilge pump.

When it is sunny, the pump sucks nutrient enriched water (horse poo) into the 18-20mm gravel grow bed, when the water reaches the surface it is sucked out with a Bell Auto-siphon.
There is enough moisture & nutrient when the sun is not available, plants do not require 24hr watering.

Plants work when its sunny, Solar panels work when its sunny too.
The auto-siphons actions allow oxygen to be returned to the plants root system.

The ongoing costs are minimal, but the rewards are maximised. (In Australia there is no z )

3

Cool, but not really the same problem. I'm trying to dispense a minimal amount of water into a flower bed sitting on my roof from a garden hose. I need the Arduino to manage when water is necessary (bed too dry), how to dispense it (don't want to flood it), and I need it to have enough power to turn on the solenoid on cloudy days too, hence the battery.

I may be could get away from having a battery by having a supercap of some sort, but that 3.4W panel wouldn't be able to supply the 6V / 300mA pulse I need to toggle the solenoid.