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Project Notes

#597 Simple Wireless Power LED

Researching wireless power transmission and building a simpel wirelessly-powered LED demonstration.

Build

Notes

The Qi standard for mobile wireless charging was released in 2011 by the Wireless Power Consortium, and since then wireless power has become pretty mainstream.

In al that time I’ve not paid much attention except increasingly as a user. But now I ahve the itch to try and incorporate wireless power in more projects.

So, this project is starting with the most basic demonstration - powering an LED wirelessly.

Construction

The power transmitter consists of a self-governing flyback oscillator, similar to circuits used in the Joule Thief. The two halves of the coil are wound in a continuous concentric circle - meaning that current flow is opposed in each half. Basic operation:

  • on startup, current flows to the base of the transistor, turning it on
  • as the transistor turns on, the current in the collector coild induces a field with opposes the flow of current in the coil to the base
  • as the the base current reduces, the transistor turns off producing a large flyback voltage spike and the cycle repeats

The receiver is a simple coild that electromagnetically couples with the transmission coil. A LED rectifies the current flow and lights up accordingly.

Breadboard

Schematic

Coil 1

The first coil tested, works fine to a range of about 3cm. Key dimensions:

  • coil wire: 0.4mm insulated winding wire
  • coil diameter: 45mm
  • base coil: 15 turns
  • collector coil: 15 turns
  • receiver coil: 30 turns

coil_01

The transmitter is oscillating at around 392kHz, peaking at 27V.

coil_01_scope

Coil 2

The second coil was a test to downsize a little: smaller coil and wire, compensated for with more windings. Also works fine to a range of 2-3cm:

  • coil wire: 0.2mm insulated winding wire
  • coil diameter: 10mm
  • base coil: 30 turns
  • collector coil: 30 turns
  • receiver coil: 60 turns

coil_02

coil_02_scope

Next Steps

This was very much a “suck it and see” experiment. It works, but the power transfered is very low.

Next I’d like to investigate increasing the power, range and efficiency:

  • controlled oscillator
  • optimal frequency and coil dimensions
  • full-wave rectification on the receiver

Some references for inspiration:

Credits and References

About LEAP#597 PowerWirelessLED
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 my personal collection of electronics projects, 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 (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.