@bmearns: And a switch - don't forget the switch, if you're gonna go to all that trouble. And I totally would.

If you wanted to make them look like fireflies in a jar, you could add a capacitor, couldn't you?

elsifer

First of all, don't buy stuff from Digi-Key if you can avoid it: Mouser or Newark generally have much better prices.

Second, and more importantly: strapping together a diode and a voltage source (like the LED and the watch battery) is a bad idea! Diodes are designed to drop a more or less fixed voltage: once you go above that voltage, the current ramps up like gang busters! So unless you match the voltage of the battery and the LED very carefully, you're asking for trouble (at these levels, probably just burning out the LED instantly).

The good news is all you need to fix the problem is some resistors, which you can also get at Mouser and Newark (yes, and DK), or even RadioSmack. The LEDs require a minimum current to light, which should be listed with the rest of their specs (like their voltage drop). The current through your circuit (and therefore the LED) will just be the voltage of the battery, minus the voltage drop of the LED, divided by the resistance of the resistor. So if you know your LED and battery, you can determine what size resistor you need. Now just connect all three in series (i.e., with the resistor between one side of the battery, and one of the LED terminals).

bmearns

These would be really cute for a party.

elsifer

Or just order a bunch of keychain flashlights from somewhere in China like Dealextreme, and get batteries, the LED, and a switch for about $.47 each.

stainlessrat

WTF? Arent those watch batteries expensive? Like holyspidoo states, solar lights are probably cheaper.

monkeyboy

This is similar to the Home Made Sun Jar project. That uses the innards of a solar powered garden light though, so no replacement of parts necessary. And the battery and LED are already assembled, so no soldering necessary.

taziar

A battery in every jar? Solar lights for exterior are cheap and better than this in every way.

holyspidoo

Some of those LED's actually come with resistors already on. That would save people some soldering.

hippytyre

Come on guys, the article is very clear: this is a setup for one night, it doesn't need switches (it also mentions that solar lights would be better for something more permanent), it's a quick and dirty way to get lighting for a party. The resistors will be needed though, at least if that night is supposed to last more than a few minutes. (There may be some led that doesn't use much current at 1.5V, but i don't think that's the norm.

rafasan

Yet another junky-looking DIY project made using garbage.

Many keychain LED lights depend solely on the internal resistance of the battery for current / voltage regulation.

Wouldn't it be easier to just use LED Christmas lights?

johnsmith1234

@bmearns: I was surprised as well when he just taped a LED to a battery and called it a day. He must not have tested that very long, but those batteries won't last long without a resistor, the LED will eat it alive.

sonar_un

First, Blue (and therefore also white) LEDs have a very high drop voltage, around 3-4V. As such, hooking them to a 1.5V cell isn't going to be the disaster some of you are painting it to be.

Second, the guys at the Graffiti Research Lab have been doing the equivalent for several years now. Look up "LED Throwie".

For a temporary thing, great idea. For a permanent thing, not so much so.

kc2idf

@bmearns: This *is* safe without a resistor-- the 3V lithium batteries have a lower voltage than the white LED forward voltage. But even if you use other kinds of LEDs, (yellow for example) the internal resistance of this type of battery is high enough that the current draw can't exceed a still-safe 20 mA. The whole point of this is to make *very easy* and *temporary* lantern. As rafasan points out, by the time that you add a resistor and switch, you have really missed the point about making it simple and quick.

The typical lifetime of LEDs in this application is 7-14 days. However, this is intended as a fixture for a single event-- you should disassemble the jars when your party is over and save the batteries for something else.

holyspidoo: The total cost per jar is as high as $1.50, if you are buying new jars. If you use existing or recycled jars like we did, it costs about $0.50/lantern. Decent solar garden lights cost *a lot* more than that, especially if you want hundreds.

oskay

@oskay: That's a good point, I hadn't considered the internal resistance of the batteries.

@kc2idf: The problem is, the site doesn't (as far as I saw) spec out what LEDs to use. If you happen by chance or know-how to get the right ones, you'll be fine. But it seemed to be geared towards people who don't know anything about electricity, in which case there's a significant risk of getting the wrong LEDs and they don't work because either they blow out, or the current is too small to light them. It's a cute idea for someone who knows what they're doing, but seems like the kind of thing that would frustrate someone who doesn't.

bmearns

@bmearns: As it turns out, any LED type will work for this. The place that you need to be careful is with the battery choice. CR2032's (about $0.25 each in quantity) or smaller types are suitable. Larger batteries with less resistance-- NiMH/NiCd/Alkaline (etc) -- can easily cook your LEDs.

oskay

Tacky. Looks like you are setting up to have a permanent yard sale on your lawn.

aj.hidell

if you really wanted to "make your own temporary outdoor lighting with cheap supplies and easy assembly" you could just drop a tea light candle into your mason jars. You wouldn't have to deal with recycling 10 or 25 dead batteries when you are done.

Jasmo

no one's mentioned the other alternative:

votive candles + sand + paper lunch bags

or... just use glow sticks (either with or without the mason jar)

chicagojohn

@johnsmith1234: I agree with you John. This project would be right at home in the pages of Trailer Park Quarterly.

ThickSkinned

I'm kind of discouraged that this sort of thing is suggested. Think of the massive amount of wasted away batteries that are going to end up in a landfill if even half of the readership uses this method once or twice a year. What a terrible waste of resources.

Desires_Silence

Here's a tip to save some money on button batteries:

[www.metacafe.com]

LD

@oskay: you hit it right on the head. I've been tinkering with LED's for various purposes for the last couple years. Lit up skulls at halloween, accent lighting outside and inside, etc. Soldering up a simple proto-board with a switch, resistor, LED, and battery can easily take 30 minutes, if you haven't already done it once. Maybe 5 minutes each once you get into a flow. Regardless, this is a fast and simple way of doing things.

Right to point out the internal resistance of the battery. As the battery dies, this resistance goes up, and less current will flow to the LED.

You don't really need the switch. Just make it possible to remove the battery easily. A good variation on this, would be to fashion a sheath out of cardstock, and sandwich the battery and the LED leads between the cardstock. Then you could slide the battery in and out of the sheath. I'll try to post a picture once I have a chance to try this.

fozzy