List of Materials
1.5- sheets plywood 1/2"
+1 sheet for the shelf
(4-legs, 4-top, 3-edge)
3.5- pieces 1-1/2"x2'x8' insulation
32 sqft hardware mesh
9216 cubic inches of sand
96' of deicing cable (spaced 4")
Glue for styrofaom insulation
Arduino (I used a mega)
Powerswitch Tail 2
ds18b20 waterproof digital temperature probe
Construction / How to Build
1) I started by making a 2x2 frame around the perimeter of one of the sheets of plywood. I then add two cross pieces to provide a bit more support.
2) Next, I ripped a sheet of plywood into 1' strips, and cut one in half to make 2 pieces 1'x4'
3) These pieces were screwed into the base to form the sides
4) I wanted to insulate the bottom, but be able to remove the insulation if I wanted to help the box cool in the summer, so I put the insulation under the table in the cavities created by the 2x2 frame. For an added touch a tapped all the seams.
5) Next, I put on the legs, in each corner I used two 1x3s at a ninety, this made a really strong leg (I thought I might have to add one in the middle, but in the end, wasn't necessary).
6) Then I put the box on its legs and lined the inside of the sides with insulation, then vapour barrier, and dumped a few bags of sand in to hold it down.
7) I glued the vapour barrier to the top of the insulation and finished it with another 1x3
8) Then I laid down the hardware mesh and attached the deicing cable with wire
9) Added the rest of the sand (7 x 30kg bags)
10) Finally built the lid, attached an old piece of greenhouse plastic and a few hinges.
I used an Arduino mega that I want to develop into my greenhouse automation controller, a powerswitch tail 2 from adafruit.com, and a ds18b20 digital temp probe in a waterproof casing. I quickly assembled it all on the breadboard and put it in a plastic box out in the greenhouse.
Next I want to automate the opening of the lid with and old garage door opener.
So far this has been working pretty well. We put our onion seedling in it out in the unheated greenhouse. -20 temps outside result in -10 temps in the greenhouse and the germ chamber kept the plants toasty at 7 degrees. The chamber does slightly better if we cover it with a few extra pieces of insulation or a blanket.