{"id":86,"date":"2011-08-21T01:54:55","date_gmt":"2011-08-21T01:54:55","guid":{"rendered":"http:\/\/greg-kennedy.com\/?p=86"},"modified":"2011-10-07T15:21:21","modified_gmt":"2011-10-07T15:21:21","slug":"joule-thief","status":"publish","type":"post","link":"https:\/\/greg-kennedy.com\/wordpress\/2011\/08\/21\/joule-thief\/","title":{"rendered":"Joule Thief"},"content":{"rendered":"

\"\"<\/a>So I had a few problems I needed to solve:<\/p>\n

* My 4 year old daughter loves flashlights, but often forgets to turn them off, and all of our flashlights use D cells or multiple AAs.<\/p>\n

* We have a large (20+) collection of “mostly dead” batteries that I feel kind of bad just tossing or recycling<\/p>\n

Both these problems are nicely solved by the Joule Thief circuit (http:\/\/www.emanator.demon.co.uk\/bigclive\/joule.htm) – an LED driver that can drain the very last bit of power from a battery and still function for days on end. \u00a0It has an additional advantage of only using a few parts, and I happened to have them all on hand… a rarity for me!<\/p>\n

I have no idea what the “ferrite” material is. \u00a0I stole this massive coil out of a broken car stereo, cracked open the plastic and found that it was actually some sort of tightly wound metal tape. \u00a0So I put the plastic back on since it was prone to damage otherwise and just ran a bunch of untwisted cat5e wires around it. \u00a0Works great. \u00a0The transistor is NPN… I assume the values of pretty much everything here really don’t matter much. \u00a0I did have problems getting the lights until I realized I had connected the wrong end of one transformer lead to the battery: the two coils must oppose one another, not run in the same direction.<\/p>\n

Of course a bare circuit is fun but not all that useful. \u00a0So I stuffed it in a little elephant toy I got off Freecycle and gave him a shiny trunk. \u00a0For now the battery is soldered straight to the leads. \u00a0One day I’ll get a real AA battery holder and some velcro to finish this up. \u00a0In the meantime he’s a good nighttime buddy for my 4 year old daughter.\"\"<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

So I had a few problems I needed to solve: * My 4 year old daughter loves flashlights, but often forgets to turn them off, and all of our flashlights use D cells or multiple AAs. * We have a large (20+) collection of “mostly dead” batteries that I feel kind of bad just tossing […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10],"tags":[],"class_list":["post-86","post","type-post","status-publish","format-standard","hentry","category-hardware"],"_links":{"self":[{"href":"https:\/\/greg-kennedy.com\/wordpress\/wp-json\/wp\/v2\/posts\/86","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/greg-kennedy.com\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/greg-kennedy.com\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/greg-kennedy.com\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/greg-kennedy.com\/wordpress\/wp-json\/wp\/v2\/comments?post=86"}],"version-history":[{"count":2,"href":"https:\/\/greg-kennedy.com\/wordpress\/wp-json\/wp\/v2\/posts\/86\/revisions"}],"predecessor-version":[{"id":90,"href":"https:\/\/greg-kennedy.com\/wordpress\/wp-json\/wp\/v2\/posts\/86\/revisions\/90"}],"wp:attachment":[{"href":"https:\/\/greg-kennedy.com\/wordpress\/wp-json\/wp\/v2\/media?parent=86"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/greg-kennedy.com\/wordpress\/wp-json\/wp\/v2\/categories?post=86"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/greg-kennedy.com\/wordpress\/wp-json\/wp\/v2\/tags?post=86"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}