build a lemon-powered flashlight!

normally it takes 3 lemons to get an LED slightly glowing...

with this design you can make a single-lemon-powered flashlight that will run for weeks!!!

credits:

it was developed during the exhibition "Cooking and Constructing" at Platform21

joule thief design

Step 1: Prepare the Components

to make this lemon light up you'll need the following tools and components...

tools:
- multimeter
- soldering iron
- steel scissors
- pliers
- sanding paper
- AA battery (for testing)
- knife
- pen

components
- lemon
- 1 kOhm resistor
- NPN transistor
- ferrite bead
- copper wire
- sheets zinc & copper
- white / blue LED

Step 2: Wind the Transformer

this transformer is the crucial element to make joule thief work with lemon. it requires much more winding then in the normal joule thief design and only plain ferrite works - all colored rings failed.

1. take about 1.5-2 meters of copper wire, bend it in half and wind the coil with it. in this case it took around 50-60 windings arranged in two layers.

2. after the winding is done - cut the double end, so that you have 4 loose single tips.
3. clean the tips from the isolation lacquer with sanding paper
4. with a multimeter set on conductivity test, find two separate windings
5. twist two opposing ends of different windings into one contact
6. pre-solder the tips of the transformer.

your transformer is ready!

Step 3: Prepare the Transistor

take the transistor and bend it's legs:
the middle one - goes straight backwards
the side ones - go forward and a bit more to the sides

afterwards - pre-solder all the legs

Step 4: Solder & Test the Joule Thief

now we're going to build the joule thief itself

solder the resistor to the middle leg

the short leg of the LED (the minus) goes to the rightmost leg of the transistor, and the long (the plus) leg goes to the LEFTmost leg of the transistor

the transformer gets one of it's single-wire tips soldered to the loose end of the resistor, and the other single-wire tip goes to the long leg of the LED

to test the joule thief - connect the twisted end of the transformer to the plus of an AA battery, and the short leg of the LED - to the minus of the battery

if the LED doesn't light up - check your circuit

Step 5: Make Copper Electrodes

1. process copper plates with sanding paper
2. cut pieces that would fit nicely in your lemon
3. pre-solder spots on the electrodes
4. cut a length of copper wire about twice the length of you electrodes combined
5. remove the lacquer from the wire in the same way you did it for the transformer
6. solder the wire to the electrodes
7. check everything is soldered properly with the conductivity test

Step 6: Make Zinc Electrodes

as zinc is not easy solderable, we'll have to use some force here

1. process zinc plates with sanding paper
2. cut pieces approximately the same size as copper ones
3. make small in the top of every piece and bend them
5. prepare the wire in the same way as with copper electrodes
6. clamp the wire with zinc pieces using pliers
7. make the conductivity test

Step 7: Stuff the Lemon

here comes the juicy part...

1. to reduce your lemon's internal resistance (thus boosting it's current output) you have to smash the lemon several times and roll it on the table until it's all soft an juicy inside
2. mark 8 cuts with as much space between them as the lemon size allows
3. make the cuts as vertical as you can and to the bottom of the lemon
4. insert electrodes in a sequence copper-zinc-copper-zinc... making sure that they don't touch each other
5. measure the voltage between electrodes
copper - "+", zinc - "-"
it should be around 0.8-1.0 Volts
6. measure short-circuit current output
in my case it was around 10 miliAmps - that's a lot for a lemon!

Step 8: Finalize!

solder the joule thief to the lemon, and you're done!
the twisted transformer wire goes to copper electrodes, and the minus leg of the LED - to zinc electrodes.

the last photo is the comparison between the freshly made lemon and the one that was running for a whole month by now.