Auto-irrigation system for raised garden using the Intel Edison

The Plan

I want a raised garden but I don’t want to have to manually water it like my lawn sprinkler system.  So I’ve been planning and gathering parts for an auto-irrigation system.  Here are the key parts:

  • Rainwater gathering system
  • Valve control to drip-water plants
  • Solar power (with solar tracking?)
  • Soil temperature and humidity sensors
  • Auto water-soluble fertilizer mixing

In this part, I’ll talk about the solar power system -specifically power storage.

Solar Power: Power Storage

I have a bunch of 350 farad super capacitors laying around.  The cool thing about super capacitors is that they can charge directly from the solar panel.  I picked up a balancer on ebay and connected six of them in series to give me about 16 volts.  I also have a spare 10W Instapark solar panel that I’ll use to charge the cells.  The Instapark solar panel is rated for 22V closed circuit.  I shouldn’t charge my super caps over 16 volts so I will need to reduce the voltage a bit.  The easiest way to drop the voltage is to use a resistor.  Using Ohm’s law we can calculate how much resistance we need:

R = V/I

My voltage drop (V) is 22V (the panel max) / 16V my super cap array max which is 6V.  The current (I) I expect to see is 600mA or 0.6A.  Plugging in my variables I get

36.66 ohms.  I want 10 watts to be safe (I figure, probably wrongly so, that a 10W resistor for a 10W panel will be fine).

Enclosures

I found some water resistant enclosures on amazon.  This was perfect size for my super cap bank.  I got an additional one to put the Intel Edison and related circuits in.  To keep it water tight, but also allow cables to get in and out I picked up 4 of these from adafruit along with matching water resistant cables.

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I used a 5/8″ spade bit to create two holes for the cable glands for the super cap box.

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Carefully I screwed in the glands and put some gasket sealer on the inside to seal some of the uneven spots from the drill.

 

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I did the same thing with the “Edison box”, but on opposite sides.

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I then stacked two power supplies on top of each other.  I got the power supplies from amazon.  They have adjustable output and a wide input range.  I have one set at 12V for the valve solenoid and the other at 4.2V for the Edison.

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Finally, I attached a power button so I can turn on and off. This too needed to be water resistant.  The white LED color is a nice touch, IMHO:

 

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Finished Power Enclosure

The enclosure works pretty well.  It took about 15 minutes to fully charge.  My hope is that it will power the Edison and friends for an entire day and most of the night.  If it turns off in the night, I can live with that.

 

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Next?

Next part we’ll look at the 2nd Enclosure for the Edison and friends.  Stay tuned!

2 thoughts on “Auto-irrigation system for raised garden using the Intel Edison”

  1. It’s been a long time since I played with electronics, but wouldn’t putting the capacitors in pairs in parallel effectively reduce the voltage to 1/2 that 22 volts per pair, or 11 volts per capacitor? Wouldn’t that be more efficient than installing a resistance?

    1. The Solar Panel can go to 22 volts. The Caps are in series to get 16 volts (6 caps @ 2.7V each) so I need to limit the panel to 16. That said, using a resistor is a terrible way to charge. I’m working on building a proper MPPT charger right now.

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