Keywon Chung Inspired Amateur

Inductive LED

2008

– Contactlessly charging LED throwies

Frustrated with the lack of slim and discrete power sources for my LED tape, I decided to build inductively charged, self-powering LEDs as a future prototyping elements for my upcoming projects.

As a shortcut to find out how inductive charging works, I bought an electric toothbrush with contactless charging feature and took it apart.

My next step was to reuse the brush side coil and build a circuit to replace the motor, and instead turn on an LED. Adam Kumpf kindly directed me to look at Bridge Rectifier circuit pictured below. This takes the AC power from the inductor coil and converts it to a DC power.

Next, I built the same circuit in a different form factor, into a small cylindrical form with magnet wire, lasercut, wood, surface mount rectifier, LED and a resistor. To make it indestructable, I cast it in 5-min epoxy real quick and made it into throwable, egg-like shapes.

Then I removed the electric toothbrush base and built my own EM surface with a function generator, resistor and capacitor and magnet coil. With 20V peak to peak and 500-600 KHz freq source, you could get over 10 times magnification of voltage. Using this custom coil, it takes the LED egg about 3 minutes to come fully on.