Step 1: Bill of Materials
The basic construction of this device is extremely simple. We're going to use some non-conductive trays and make a sandwich of aluminum foil, paper towels and a carbon brush electrode which begins its life as an aquarium filter.
You're going to need some non-conductive tray containers. I used some carryout containers from a local rib joint but almost any tray may be used. Since there only two dinners I used two bases and one lid. The common glass 9X11 glass cooking trays would be perfect.
3 paper towels to act as the porous layer.
A box of carbon aquarium filters. I used the Fluval brand of carbon pad replacement filters available at PetSmart for about $4. These come 4 to a box, I used the "4 Plus" size. These are used as the carbon electrodes in our assembly and function in this role quite nicely.
Some salt to use as an electrolyte. Ordinary table salt is fine, you'll need about 5g to start with. That's approximately 1/2 TBSP. In a liter of water that should produce approximately a 5% solution. Feel free to vary electrolyte strength.
A solar yard light. (see picture). These are available at most hardware stores for about $4. This is a self contained solar powered light with a rechargeable battery. it works by using a joule thief type circuit to maximize energy stored in the battery, the difference being that this circuit uses a capacitor rather than a traditional toroid so it doesn't provide the power amplification normally associated with a joule thief. NOTE: In the joule thief circuit the toroid provides both power amplification and capacitance.
4 electrical leads with clips, these are available from Radio Shack in a package of 12. These are used to make all connections.
A scissors, ruler and ball point pen along with a small screwdriver for dissassembling the solar light.
Now let's get started...