The Potato Battery

Supplies:
          I   Copper coin (+)
         :I:
       :::I:::  Potato or banana (Electrolytes)
     :::::I:::::
   ::::::::::::::::
----------------------------Aluminum foil. (-)

The Copper: I use a penny. 
You can use bare wire etc.

Electrolytes: You can use other fruit  (orange, apple etc.)
I used 3-4 cells in series to get enough voltage to run LCD clock.

How to Make a Potato Clock

You can find the Two Potato Clock kit for $20 or so in school science
catalogs. You supply two potatoes, connect some electrodes, and the clock runs
on electricity provided by the potato. You can also do this without buying the
kit. Many inexpensive LED clocks run on a 1.5-volt button battery (for
example, Radio Shack #63-736). To run it on two potatoes, you'll need:

* Two copper electrodes. A 10-cm length of thick (0.64 cm) copper ground wire
works well. You'll find it at hardware and home supply stores.

* Two zinc electrodes. Use large galvanized nails, also available from a
hardware or home supply store.

* Three alligator-clip wires (Radio Shack #278-1156).

* Two potatoes.

Now make a potato clock. Open the battery compartment of the clock and remove
the button battery. In the compartment, notice that there are two connections
for the battery marked plus (+) and minus (-). You'll connect the potato
battery to these two places. Let's call the potatoes A and B. Connect A and B
to the clock like this:

1. Insert a copper electrode and a zinc electrode into each potato, fairly far
apart.

2. Use an alligator-clip wire to connect the copper electrode of potato A to
the plus (+) connection in the clock.

3. Use an alligator-clip wire to connect the zinc electrode of potato B to the
negative (-) connection in the clock.

4. Use an alligator-clip wire to connect the zinc electrode of potato A to the
copper electrode of potato B.

That's it. If all went well, the clock is running and will run for a long
time. Our project student Jennifer started one in April and it was still going
strong at the end of the school year.