I started the mini-greenhouse as a demo project, rather than one that would produce significant food quantities. First thing is the frame, which represents the structural and the functional. A good frame will ensure a stiff greenhouse, and small tolerances in production will help you down the road (e.g. sticking the acrylic panels).
I cut all the frame elements from a single piece of discarded plywood panel, which is a multilayered wood panel. I made 8 pieces of 20x20x300 mm and 4 pieces of 20x20x170 mm. In order to assemble the frame, 4 of the long spars and all the small spars need a small symmetrical groove at both ends. You can do this by cutting the wood halfway and then using a chisel to remove the excess. Careful not to split the wood at this stage, one of my spars got easily damaged.
Step 1: Building the Frame Spars
This is how you want to assemble 8 of the 12 spars. You can make adjustments in the process by sanding the wood and making it fit as good as possible. Again, this will help you later.
After reaching an acceptable fit, go ahead and drill one 3 mm hole in each joint, careful not to go through the other side but making sure you got both pieces. You can see two holes in the picture but I ended up with one screw in each joint. You need wood screws, and always drill the hole one size smaller than the screw.
Step 2: Assembling the Frame
Next, the other 4 pieces of the frame will be attached, forming the skeleton of the greenhouse. This is tricky for some people if you haven't done any woodworking before. But it looks more difficult than it actually is so don't worry.
The principle is to join these pieces by a wooden chip, which I also salvaged from a broken kite frame. In order to do this, you have to drill both pieces of wood, making sure that the wood chip will fit in diameter and length. This time you have to drill a hole with the same diameter as the joining element. Put one drop of wood glue in one of the holes and hammer the wood chip in. For the final assembly, put some glue in the hole of the second piece, and around the wood chip on the first piece and carefully hammer them together.
Step 3: Side Panels
I chose to have a greenhouse open to the environment, ensuring air circulation. The side panels are made from acrylic glass which was laser-cut in AxB pieces, with a 2 mm thickness. I used regular superglue to attach the panels to the wooden frame. Next, I attached some hinges, one side to the frame by regular wood screws, the other side also by screws which had their ends cut off in order to be able to close the door. Another trick you can make is having a hole or a groove where the ends of the screws will come into place. One final touch is to drill 2 holes in the acrylic door, through the frame. The screws will act as a door stopper.
Step 4: Fitting the Water Tray
I found the perfect size of a water tray in the packaging from the folding solar panel that I will use to power the greenhouse. Some small adjustments using a cutter knife were sufficient. This was later filled with cotton, acting as a growing medium.
Step 5: PC Fan
I used a PC fan for my design, which I fitted through a side panel. I cut the panel in a rectangular shape but would have fitted better in a circular fashion. You can see in the second picture how the top panel got unstuck from the frame, probably because of trying to fit the fan after mounting the panels. The fan is connected to an Arduino unit, and turned on whenever the temperature gets too high inside.
Step 6: LED Bulb
I mounted the LED bulb on the frame. It's also connected to the Arduino unit, which turns it on based on a light sensor reading. The sensor has to be placed out of range of the LED, such that they do not influence each other. The theory is that when the light readings are below a preset threshold, the LED will light up, ensuring the necessary light amount for the plants, limited by the battery.
Step 7: Arduino
Now the fun part. I uploaded the Arduino code here: https://tinyurl.com/yck3cpj8
I would have never managed this by myself. All credits go to Aidan Wyber, who helped with the circuit, code and making it all work. I did the soldering. The system can be said to contain the following elements: light sensor, temperature sensor, solar panels, battery, PC fan, LED bulb. The solar panels will charge the battery during periods of sunlight. This power can be used to power the fan and the LED, which are triggered by the two sensors.
Step 8: Final Result
My demo apartment greenhouse looks something like this. I added a wooden panel bottom and I raised the water tray, which is a bit crooked. All the electronics are under the water bed, which is a risky thing to do. My next design will reserve space for the electronics above the plants and the lights, which also helps dissipate heat from all these components.
This project has been part of the PHABLABS Challenger projects: http://phablabs.eu/photonics-challenger-projects