My now retired co-worker gave me a present with some bars of Blissed Out Soap, which gives a website on the wrapper. I have been fascinated by homemade soap since I was a child, and watched our next door neighbor make soap out of bacon grease and lye (sodium hydroxide). This soap is very fragrant, smells great, but I haven’t had a chance to try it yet – all in due time. While I was there, I typed in LED into the search box at the top and came up with some very interesting stuff under LED lamps. One, a retro style lamp, caught my eye. I’m not sure if it would be called Steampunk, a name which seems to be applied to anything that is new but eclectic and antique looking. I really like the look of this lamp, but one thing that really concerns me: how long the LEDs will last. I have done lifetime tests on LEDs, and these small LEDs often last less than a thousand hours. Someone gave me an inexpensive LED tamle lamp with a row of a dozen 5mm white LEDs. I had it running for much less than a year and the LEDs all became dim, and it was useless as a light. It’s not such a big deal when the lamp costs ten or so dollars, but when the lamp costs hundreds of dollars, this becomes a serious issue. I could open up the table lamp and replace the LEDs; one cannot open up the glass envelope of this expensive lamp and replace the LEDs easily.
Another one that interested me was a submersible LED light. It’s a really good idea, because LED lights are often used where the weather is wet, or in high humidity environments. They’re cheap too; ten for ten dollars U.S.
Looking through the LED lights, I saw that many used a CR2032 lithium coin cell. One reason they use these is that the 3V cell can power a LED by itself, with no resistors or other circuitry. The internal resistance of the cell is enough to limit the LED current. Those keychain LED fobs that we see in the checkout line do the same thing: they connect the cell directly to the LED. One product said that the cell lasts for 48 hours. After looking at other products, observation is that there is considerable room for improvement in the technology used in these products. First off, with the technology used in a Joule Thief, the designer could be freed from using multiple coin or button cells. And with my Supercharged Joule Thief circuit, the battery life could be extended considerably.
But for seriously long battery life, and given the limitation that the LED must flash, my Blue Blinky circuit would allow the LED to flash for more than a year on a single AA cell. A Christmas decoration with up to a dozen LEDs would be able to run on a single cell for a month or more, which is long enough to get it through the Xmas season. The LED color does not have to be limited to blue; other colors could be used. And with surface mount parts, the board with a half dozen or more individual circuits would fit in the space of a AA cell. Also, there is a flashing Red LED circuit (see my blog) that does not use an inductor, instead it uses a switched capacitor, AKA charge pump. This would save the expense of the toroid core and winding the JT coil.