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Project Notes

#137 ToroidJouleThief

Test a Joule Thief circuit based on a ferrite toroid.

The Battery Pack Build 2


This circuit achieves a voltage boost, enough to drive an LED with forward voltage in excess of the power supply. In fact it can continue to run the LED as the battery is depleted. I haven’t tested this yet, but apparently it should work down to a battery voltage of ~0.3V under load

The circuit is all over the internet, but I used RimstarOrg’s video as a guide.

In this circuit I’m driving a 5mm white strawhat LED, with a forward voltage of 3-3.2V. No small feat for a single 1.5V AAA!

Winding the Toroid

I used an 18mm ferrite ring and 30AWG solid core wire. The two wires are wound in a pair in the same direction - about 10 turns - but they are connected in reverse in the circuit:

Winding In From Out To
1 V+ Collector
2 Base 1kΩ->V+



The Schematic

On a Breadboard..

A 1.44V AAA supply running the LED..

The Build

Squeezed into Battery Pack

Fits a single AA or AAA battery, with a switch added for convenience. Makes a decent night light..

The Battery Pack Build

Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.