In this project I am going to show you how to make a joule thief and put it in a jar. This joule thief is a simple circuit that will take an old “dead” AA or AAA battery and up the voltage enough to power an LED. I use these as decorations and to completely drain batteries that are too “dead” to work in other devices. Note: The only unique idea here is to stick one of these circuits into a plastic jar. The circuit is not mine. I learned how to make these circuits by following this Instructable and this post on EvilMadScientist.
To make a joule thief you need a AA or AAA battery holder, a 1k resister (or similar), a 2n3904 transistor (or similar NPN transistor), an LED, a ferrite ring, some wire, a project board (optional), and common soldering supplies. This is an easy soldering project and one that would be a good first project but I am not going to explain how to solder here.
Most of the supplies can be found at your neighborhood electronics store, online, or scavenged from other electronics. I found ferrite rings at Ax-man, the greatest store in the history of all mankind. You can also salvage ferrite rings from old inductors or other ferrite toroids. You don’t need a very large project board. I used the smallest one I could find and cut it into smaller pieces with a Dremel tool. You could also build the circuit freehand.
Below is my drawing of the circuit. It is by no means a true schematic but it was helpful to me. Here is a much better schematic.
The most difficult part of this project, and it isn’t that hard, is to hand wind a ferrite toroid. You need 2 lengths of wire. I like to use magnet wire because it is thin but you need to use sand paper or a sanding wheel on a Dremel tool to take off the coating from the ends of the wire to solder them. This is a little harder to do than stripping traditional wire but not too bad. Holding the wires together, put them into the ring and wind them around the ring 8-11 times keeping the wires parallel to each other.
Connect the beginning of 1 wire to the end of the other wire (see photo). This will be connected to the positive (+) end of the battery.
Solder the other components as in my drawing or the schematic. I didn’t have any 1k resistors so I used an 820 ohm resistor and the circuit works just fine. I’m probably burning through batteries slightly faster than if I had used a 1k resistor, but I’m OK with that. The 2N3904 transistor has 3 pins; the emitter, base, and collector. See the diagram to determine which is which. The collector (C) should be soldered to the positive (+) end of the LED and 1 wire from the ferrite toroid. The base (B) connects to the 1k resistor. The emitter (E) connects to the negative (-) end of the LED.
New LED’s will have 1 long pin and 1 short pin. The long pin is positive (+) and the short pin is negative (-). The base of most LED’s have 1 round side and 1 flat side. The pin on the flat side is negative (-).
I used a blue LED because I like blue LED’s. You can use most any LED for this project. You can even use 2 or more LED’s in parallel but the brightness of each will be slightly reduced. I have tried flashing LED’s and I have found that they don’t usually work too well.
I found some small, semi-transparent plastic jars at Ax-man. By shoving the battery and circuit into a jar, I was able to make a little jar of light powered by a “dead” battery. I think it turned out well and the light is pretty bright.