Introduction: Joule Jar Lantern (a Joule Thief Driven Decorative Glass Jar LED Light)

The batteries of your tools are not yet empty?
But the flashlight doesn't work any more? No problem - with the Joule Thief! And it's quite easy to build.

What is a joule thief? This is a tiny circuit allowing you to operate a white or different coloured LED from a low voltage. For driving a LED you normally need 3-3.5 V, as from a 3 V lithium button cell. But with a 1.5 V battery (like a Mignon / AA cell) it doesn't work at all. With the Joule thief, however, it magically works: not only with a new battery, but until the battery is nearly dead - down to 0.3 V. This is far below the point that other toys still can handle.

The Joule thief can steal energy from the battery - every last joule (that's what it's name comes from). Many Joule thief i'bles can be found here so I'll kepp this part short. What we do here is putting the device into a jar and make a looped wire hanger around the jar's neck to hang it somewhere in the house, the garden or tent.

Now you can put some seasonal stuff inside the jar, under the LED, getting nicely illuminated!

Step 1: What We Need...

For this project you need:

1 transistor 2N3904 or BC548
1 resistor 1 kΩ
1 ferrite ring core (e.g. 12.5 x 7 mm)
1 battery holder for AA cell
1 used battery (1.5V)
approx. 22 cm double wire, insulated

soldering iron
PCB holder

some wire, maybe from wire hanger
small nail
glue gun and hot glue stick

The small electronic parts I had bought from I paid about 1 $ for 100 transistors or LEDs. The most expensive thing was the ferrite ring core (toroid). It was about 10-20 ct each.

Step 2: Some Soldering...

We start with the ferrite ring core and 22-30 cm of the differently coloured insulated wire pair: wrap those around the core to form a coil. To wind up your coil start with holding 4 cm of the wire in one hand and put the other end into the ferrite ring core. Now wind the wire around the core. The winding direction doesn't matter. The wires should be close to each other and always parallel. So, in my case, the red wire is always on the right side. Repeat this step at least 7 times - the more often, the better.

Only one layer should be around the ring core. Note that we have two pairs of wire ends: one comes out at the front, one at the back. Take the stripping pliers and remove the plastic isolation of the four wire ends about 1 cm. Then take a wire of one colour from the front and put it together with one wire end from the back with the different colour. Twist them a little. Solder the couple now together. This is the "common point" of the coil windings. In the circuit diagram for the Joule thief, the common point of the ring core is the connection at the top, in the upper right corner of the circuit diagram. This is connected to the positive pole of the battery (red insulated wire of the battery holder). The two other wires from the ring core are soldered later a) with the resistor and b) with the junction of the transistor ("C") and the LED.

Another detail is the symbol and the assignment of the legs of the transistor. In the symbol, the part marked with the arrow is the "emitter" ("E"). The "collector" ("C") is the leg above it in the circuit diagram, which will also be connected to the LED. The "base" ("B") is the leg guided to the left in the diagram, in the middle between collector and emitter. Hold the transistor's legs in your hand the way that you can read the text on the flat side. Then the legs are from left to right: emitter, base and collector. On the underside there may also be written "EBC".

The LED's short leg with the flat side is the negative one. The positive leg is the long one. To solder both LED and transistor together, simply put the LED's legs over the transistors outer legs: The short leg of the LED over the left leg of the transistor ("E") and the LED's long leg over the right leg of the transistor ("B"). Before soldering them together, take the middle leg of the transistor ("B") and carefully bend it down. Now you have more space for soldering. Already finished? Well done! Your first peak of the Joule thief is done now!

Step 3: Resistance...

Now easily solder the middle transistor leg ("B") to the resistor (Note: In the photos I had done this step first, before soldering the LED to the transistor, so don't worry. The sequence of doing these steps doesn't matter). Now also solder the right leg of the transistor ("C") to one single end of the ring core wires (the colour doesn't matter). Take the other single end of the ring core wires and solder it to the other side of the resistor.

Step 4: Last But Not...

Last part of your Joule thief circuit: The battery is connected with two wires. Solder the red wire (from the positive pole) to the two twisted wire ends of the ring core. Solder the black wire (from the minus pole) to the connection of transistor's emitter (left sided leg) and the LED's minus pole (short leg).

Instead of using a battery holder you can put a rubber tape around the battery and keep two wires clamped with the rubber tape to the battery's poles. Take care of the plus and minus on the right wires! With this model you can use different sized batteries, but all of them should have had 1.5 V when being new.

If you like to add a switch or button, cut one of the battery wires and solder the switch between the two wires. Now you can easily turn your light on and off!

Step 5: Housing Your Electronics...

For making a flashlight, just use any small case as a housing and drill small holes for the LED (mostly 3 mm or 5 mm) and the switch, if you're using one, in it. To fix the electronics to the housing I used hot glue because it's most versatile and hard within a minute or less. Take care of your skin when using it - it'll get really hot and can burn your skin while sticking onto it or damage your clothes.

You can install your tiny Joule thief in a jar. Then your Joule thief powered jar light features a timeless mason jar design and comes with a tight waterproof seal that makes it ideal for either indoor or outdoor use.

Alternatively, you can put it in the lid of a large glass. The LED now illuminates its contents. You can decorate it according to the season, e.g.with dried fruit, sand, dried flowers, shells, pebbles... Unlimited scope for personalisation and makes a great gift!

Step 6: Hang It High...

Around the neck of the glass you can bend a wire (e.g. from coat hangers) to hang or mount it somewhere.

Now you need some powerful pincers (pliers). First, cut off the hook of the hanger. Then bend the wire with a pair of pliers to a straight piece. Use the pliers again to bend one end to an eyelet. The eyelet's shape doesn't matter. Then bend the eyelet again at an right angle.

Now bend the wire around the neck of the glass. The wire should have now the same radius as the neck of the glass has. After a quarter turn around the neck again bend an eyelet into the wire. After that bend the wire again around the neck. On the opposite side of the new eyelet bend a third eyelet into the wire. The two new eyelets later are fixing points for the hanger.

Bending the wire again around the neck will lead the wire to the first eyelet. Close to this first one you should bend now the fourth eyelet. The distance between the two can be around 1 cm. Now cut the wire behind the fourth eyelet.

To press the first and the fourth eyelet together, take the rest of the wire and bend an eye from its end. Cut this eyelet and put it into eyelet number one. Now press eyelets number one and four together and try to press eyelet number four as well into the new eyelet. Congratulations, you made part one!

Again, take the remaining piece of wire and bend one end to an eyelet. Press this eyelet into eyelet number two. Bend the wire piece somehow into a round shape and bend an eyelet into its other end. Put this eyelet (number seven?) into eyelet number three. Finished? Giant Congratulations! Now relax your fingers and enjoy your new mason jar light, wonderfully decorated, water resistant and powered by a Joule thief!

Step 7: Spooky Decoration...

A more spooky decoration alternative is putting liquid into the jar. You can...

- Take the hot glue gun and put some thread-like structures around the jar. This will make it look like a spider's web.

- Cut a text marker, remove the colour keeping inner part, and pour it into a glass of hot water (like tea). I prefer the yellowish flourescent ones. Now you better put the battery holder to the outside of the lid. For doing this, poke two small holes with a nail and a hammer into the lid, cut your battery wires in the middle and put them through the lid holes into the jar. then solder them together as they were connected before. Glue the battery holder to the top of the lid and the electronics in the interior. For the yellowish flourescent liquids better add a UV LED instead of a white one. Seal the electronics in the lid with lots of hot glue to get them waterproof.

- Put water into the jar and add some glitter. As in a snow globe you have to shake it to get the glitter mixed with the water. Better add anything that keeps the glitter mixed in the water. This could be starch or superabsorbent polymers (also called slush powder). You can find them e.g. in sanitary napkins or diapers. Simply cut open the diaper and pull out the fibrous superabsorbent polymers. Add it in the jar and mix it with water, glitter and maybe some colour. In this case keep the LED white. Any other LED colour will do the job as well.

I wish you lots of fun building the Joule thief glass jar lantern! Did you make it? Please, post your results here!

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