10 Aug 2009
This month's Practical Wireless makes reference to something called the Joule Thief circuit which allows a very nearly exhausted single cell battery to run a white LED. The article is in G3RJV's regular column. The nifty circuit only needs 4 parts. For a video describing how to build this, see this YouTube item. Another useful resource is http://www.emanator.demon.co.uk/bigclive/joule.htm from which this image was taken.