I blogged a similar light recently, but I didn’t get a good closeup picture of the parts laid out on the back of the AAA cell holder. This time I got a good photo of it before I coated it with clear silicone sealant (I did get a good closeup, it’s in the linnk above). I did not include an on/off switch because I figure these are made for a single use, and will be kept around in some drawer and possibly disposed of soon after use. And I’m too cheap to spend $2 or more (USD) for a switch that actually costs more than the rest of the light. I just cut a small piece of heavy paper or cardboard from a cereal box or whatever and stuck it between the battery and the contact. When I need the light, I just pull out the paper.
Which brings me to the cost of the parts. The LED was somewhat expensive, since it’s a Nichia that I bought a long time ago and probably cost a dollar. Today anyone can get 9 of them in a cheapo flashlight that costs $2.00 (See Note). The PN2222A transistor was less than 5 cents or five dollars for a bag of 100. The resistor was pulled from a board, but they’re about 2 cents or $2 per hundred. The toroid core was from Surplussales.com and cost about $.25, (ICH T231212T) and the wire was 30 AWG and cost very little, probably a few cents, since a quarter pound reel was about $15 but there are over a thousand feet of wire on it, and I used only about a foot.
Back to waiting for the silicone seal to dry so I won’t get sticky fingers from handling the light. 😉
Note: Some might wonder why I would pull apart a good flashlight (torch) with 9 LEDs to make one with 1 LED. Well, the 9 LED light gobbles three AAA cells at a time, and doesn’t run very long on a fresh set of 3. I have bought several of the Fenix LD01 flashlights, and they put out so much more light and use only a single AAA cell, and they’re so small I have one of them on my keychain. So I will not use one of these cheapo flashlights, I just take out the LEDs and scrap the rest. I tried using one of them for some other project, but after a year or so the plastic case became sticky and gooey, and melted into whatever it touched. It was making a mess, so I don’t leave them around anymore. Besides, I now have a single cheapo light that fits just about anywhere and runs off a single AAA cell. And I’m proud to say I made it myself.