Build a Joule Thief circuit to power LEDs from dead batteries. Complete circuit diagram with toroid, working principle, components list & step-by-step assembly guide.

It's a known trick that we can use LEDs in reverse. We'll explore how to use them as photodetectors with Arduino and create a simple demo that responds to hand swipes.

In this arduino based project we are going to interface a 5 RGB (Red Green Blue) LEDs with Arduino Uno. These LEDs are connected in parallel for reducing PIN usage of Uno. Check out the complete tutorial here.

This lesson will basically get you up and running using the Arduino software and uploading a sketch to the Arduino board. Once you've completed this step we can continue to the really exciting stuff, which is when we start writing our own sketches!

In this Instructable, I first demonstrate how to build the complete circuit on a breadboard using two NPN transistors and two LEDs. Once that circuit is built, I demonstrate how we can break the circuit out onto a circuit we will draw with your CircuitScribe pen!