2013-06-25 Paul’s Joule Thief

Paul has been busy creating little Joule Thief Jewels out of salvaged household items such as CFL ‘corkscrew’ light bulbs.  He has given me permission to post one here.


This is also a cork supported one. I used a reclaimed toroid with 15 turns of new enamelled wire for right winding and a reclaimed double length feedback left winding. The coil is fixed with nail lacquer. A high gain 670 hfe BC 337-40 transistor and a 47kΩ resistor makes it very light sensitive with the LDR. It still draws 20 mA but is bright and oscillates at 160 kHz. The solder joins are recessed in a carved out area in the cork top section covered by the residual sliver of cork as a base. The wires were positioned with hollow needles to guide them. It looks good with exposed bits but also light and retro. The cork supports and insulates very well. It is so light sensitive that it dims when near any reflective surface even clean glass as the reflection affects the LDR. That means it will not work well in a glass jar. The connectors are made of thin floppy silicone wires. Floppy wires work very well with magnets.
Overall fewer right turns seem fine and high gain transistors seem to be more useful than high power high current ones.

I really liked the look of this one for some reason – brings to mind Wynkin, Blynkin and Nod, maybe because looks like it could sail off on a voyage since it’s cork, blinking as it fades into the distance.  I thought I might be able to add a few ideas, so here goes.

We do not have fireflies here in So. California, so I thought it might be a good idea to try to make a substitute. My idea is to change the circuit to a Joule Thief flasher, and use a button cell for power. A small slot cut into the cork should serve as the battery holder.

Then waterproof the cork with coats of polyurethane sealer. The LED can be mounted at the end of a stiff wire so it is a few inches above the cork.

Several of these can be floated on the surface of a pond with running water. The motion of the water will cause them to move around the pond as they blink. The effect is to give little blinking lights hovering over the water at night. Since I really have no idea how fireflies act, I can’t say if this is a close substitute for them, but it should still give an interesting effect, as long as the cork stays afloat. The trick is to make sure it doesn’t get top heavy and capsize. But then it might be cool to have some blinkies under water, too.

Another idea. Leave the cork round so it will fit in the bottle. Mount the battery and LED on a length of stiff wire so they go inside the bottle and illuminate it. Use a bottle with colored glass for enhanced effect.

I was out for a walk and found a ball in the middle of the street, blown out there by the wind. The ball is made of clear plastic, and it’s hollow, and filled with what looks like water. In the water is this object that starts to blink brightly when the ball is bounced. I see kids wearing shoes with similar LEDs in the soles that blink whenever they step. Nowadays these can be found just about anywhere there is a toy or some item for the kids.

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