Simple Joule Thief

Wikipedia says :

A joule thief is a minimalist self-oscillating voltage booster that is small, low-cost, and easy to build, typically used for driving small loads. This circuit is also known by other names such as blocking oscillator, joule ringer, vampire torch. It can use nearly all of the energy in a single-cell electric battery, even far below the voltage where other circuits consider the battery fully discharged (or "dead"); hence the name, which suggests the notion that the circuit is stealing energy or "joules" from the source – the term is a pun on "jewel thief". The circuit is a variant of the blocking oscillator that forms an unregulated voltage boost converter. The output voltage is increased at the expense of higher current draw on the input, but the integrated (average) current of the output is lowered and brightness of a luminescence decreased.

I say it's a fun little weekend project that can be done with very few parts (even salvaged) and discharged/dead batteries.

Parts

• 1 Red LED (or any other color)
• 1 2N3904 Transistor (or equivalent)
• 1 1k Resistor
• 1 Toroid
• 2 Thin wires, different colors
• 1 Battery holder

Tools

• Soldering
• Iron Solder
• Helping Hands

TIP: You can salvage the toroid and transistor from a dead CFL bulb.

Wind the two wires around the toroid while making sure you don't twist the wires, and also make sure that two wires of the same color are not right next to each other. Keep winding, making sure you wind the coils as tight as possible.

You need approximately 9-10 turns on your toroid and make sure the turns are spaced evenly around the toroid. Once you wind around the whole toroid, cut off the extra wire, making sure you leave a some for soldering. Take a wire from each side, making sure they have the opposite color and twist them together, now you're done with the toroid.

Solder all the parts following the schematics.

First solder the resistor to the middle pin of the 2N3904 transistor.

Then solder the LED to the outer pins transistor, keep in mind the polarity of the LED, the long pin is the ANODE (+) and the short one the CATHODE (-).

The twisted wires from the toroid go to the positive wire of the battery holder. The white wire from the toroid get's soldered to the resistor and the red one goes on the positive pin of the LED.

All that's left is to solder the negative wire of the battery holder to the negative pin of the LED and we are all done.

Add a battery and if the LED goes on that's it, you have successfully completed the project !

• Put all the parts on a breadboard.
• Add light dependent resistors (LDR) to only light up the LED at night.
• Put everything inside an enclosure.

Hope you enjoyed this project and if you have any questions feel free to ask.

Thank you for reading!