**--- DRAFT ---**

Last Edit: BK 2024-11-02

The Joule Thief

A quick, fun project that lights an LED (or string) with an otherwise useless battery

Brief Overview

The workshop will let participants build a small project in a short period of time that they can then take home. It uses a small number of inexpensive parts that are supplied. Participants will learn soldering skills (as needed) and learn something about electronics.

Required Materials that DMS / Library will supply:

• 1 2N2222 transistor
• 1 1K Ohm resistor
• 26" 0.2mm / 32 ga. coil winding wire
• 1 AA battery holder
• 1 White LED
• 1 small ferrite ring
• 1 mostly weak AA battery (0.6 - 1.5 volts)

Required Tools that DMS / Library will supply:

• Multimeter
• Soldering Iron, solder, flux
• Wire stripper
• Small Needle Nose Pliers
• Sharpie marking pen
• Li coin cell battery

Explanation

The Joule Thief uses the weaker voltage of the battery to temporarily store energy in a magnetic field using a magnetic field in a circuit controlled by the transistor. The energy is stored in the magnetic field which collapses when the transistor turns off, sending the energy as higher voltage electricity to the LED approximately 50K times a second creating the appearance of an always ON LED. The voltage created is high enough to not only run a single LED, but also a string of LEDs connected in series. For more information just search the web for the string <Joule Thief>.

Steps

Cut a length of the fine coil wire that’s about 26" long. Fold it in half. DO NOT CUT IT. On one half, let’s call it the A side, use the Sharpie to mark both ends of one side. You’ll need to find the 2 ends of one side when you’re done winding. Use pliers or any tool to make the fold nice and small. You’ll use the folded end to thread through the ferrite ring.

Thread the wire through the ring so that you end up with about 20 windings of the doubled wire.

Cut where you folded the wire.

Find the two ends of the A side that you marked with the Sharpie.

Join one A beginning to the B side end (See illustration) with a solder joint.

Trim the leads on the battery holder to about 1/2".

Solder the coil leads that you just joined to the positive (+) lead of the battery box.

Solder the 3rd coil end (it doesn’t matter which you use, either is fine) to the Collector of the transistor (see illustration).

Solder the 4th coil end to the Base of the transistor via the 1 K resistor.

Solder the positive end of the LED to the Collector / Coil end junction. If you’re unsure which are the positive and negative LED leads you can test with a coin cell battery.

Solder the Emitter lead to the negative battery lead.

Solder the negative end of the LED to the Emitter / negative battery lead junction you just made.

Test with a battery to see that it works.

When done, you can fold all the wires next to the case with the LED poking out the end and then use a hot melt glue gun to encase all the parts.