My solar powered device charger (based on this design), which I’ve taken to calling my SkyJuicer after all my references to the sun as farm fresh and whatnot, has been working incredibly well. My personal cell phone has been charging exclusively through the sun’s rays for nearly two weeks now and neither it, nor the juicer, has run their batteries down. However, I haven’t soaked up enough sun for the LiPo charger chip to list the battery as ‘full’. Hardly a problem.

The only design tweak I’d make so far is switching from normal craft-worthy hot glue to high-temperature hot glue. Saturday, after a few hours in the intense morning sun, I could smell the glue softening. I don’t think it’d come loose, but, you know.

Anyway, it’s success got me thinking again about my next project. We’ve been talking about putting in a garden, but our intense laziness has at times been a problem with those in the past. Taking some inspiration from the automated indoor gardening manager, the Garduino, I’m thinking I can strip it down and make a solar watering device.

The Garduino measures soil moisture, light, and temperature. Since we’ll be doing this outdoors, the latter two aren’t really going to be needed… here in Georgia we have a great, lengthy growing season. I put together a simple circuit last night based on a 555 timer. If one switch gets cut, it can activate a device on the other end. I wire that switch as two nails in the dirt: when current between those two stops, there’s not enough moisture, so it turns on power to a 12 volt DC submersible pump. The pump can sprinkle water on it until the connection is re-established.

Two 6v panels wired in series will provide the 12v for the pump and the whole circuit: this likely won’t need to run at night. Also thinking about a wooden frame to cover the small plot so I can screen it in and keep pests out… of course, that’d probably draw police like a magnet and they do so like to cruise around in their helicopter. Maybe not.

I’ll have to experiment with the circuit, of course. 12v in the soil between two very-close nails isn’t going to kill the plants, of course, but if it’s excessively sensitive (overwatering) or insufficiently sensitive (under-watering), it’ll kill them in other ways. Plus there’s the question of where to get the water, though we already decided a rain barrel would be perfect. But that’s a detail for later.