2 minute LED flashlight from SD card case

Using a high brightness LED, two calculator batteries, a little piece of wire, and an SD card case, I created this really spiffy little pocket flashlight in about 2 minutes flat.

Step 1 Connect the batteries

Using electrical tape (I chose white) and about 3/4 inch of wire, connect the two batteries in series. Using a longer piece of tape on the back side, I also taped the positive lead of the LED to the first battery, laying the other lead (the fuzzy line in the second pic) over the negative terminal on the second one.

Comments

[LaserDave]

@dean-101 You are right dean...mostly. Although I may have missed it, the voltage of the batteries was not mentioned, so these coin cells can be either 1.5v or 3v.

If the batteries are 1.5v each, then you don't need a resistor for the 3v total because the white LED wants to see 3.4v. Funny thing about white and blue LEDs, they have a "threshold" where they run up to full brightness only between 3.2v-3.4v. When they are fed from 2.5v-3v they tend to just "glow" at around 1/2 brightness - but the LED will last forever, and so will the battery with such a low current draw (somewhere around 5mA at this voltage).

If the batteries are 3v each (which is most likely here), then you have a 6v total and you should use a resistor.

There are two ways of looking at this scenario however.
1- do you want to run this thing for the next decade reliably? If so, a 100 Ohm resistor would see that it lasts good and long.
2- do you want lots of light for short periods of time and don't care about living past a year or two? Then don't bother with the resistor. BUT - even with the batteries' internal resistance, you will still get 60mA to 80mA across the LED which will make it get warm. Heat is what kills LEDs, so if you use the circuit wisely with minimum on-time (or provide heatsinking for the leads as close to the LED base as possible) you will still get fairly good lifetime...and lots of bright light.

* for what it's worth - one way of "heatsinking" a bare LED is to make a bead of epoxy (the good stuff that hardens like "glass") across the leads at the base of the LED, which can also serve to cement the LED into its enclosure.

[meskalin64]

You only need a resistor if the LED is getting to much voltage.

[doo da do]

On several Make LED projects everyone seems to have a resistor. This one does not seem to have one, would that make it better? it appears to work just fine without the resistor. just curious

[hammertong]

The run time the manufacturer states is not the life of the LED, that is just how long it will work at maximum efficiency. After that time, or when you start to burn it out, the LEDs just become more dull. Plus when you can buy 20 LEDs for $2, who cares if you burn them out?

[redgator12]

Haha 20 for $2? I just bought a 100 pack of red, blue, green, white, and yellow for $6. That's 5 times more for 3 times the price. It's on eBay, and it's got free shipping. Here's the link: http://cgi.ebay.com/100-Pcs-5mm-Red-Blue-Green-Yellow-White-Amber-LED-Light_W0QQitemZ110383173587QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item19b3598fd3&_trksid=p3286.c0.m14&_trkparms=65%3A15%7C66%3A2%7C39%3A1%7C240%3A1309%7C301%3A1%7C293%3A1%7C294%3A50

[dean-101]

it is best to add a resistor because they DO make your led last longer before burning out. when an led is connected to a battery even 3v it is still getting a little too much power so a resistor takes all the power and heats up to lose some power. this will make the led last a LOT longer.

[Instructabilis Deus]

Yeah, I just copied the way all my little truck stop LED keychain lights work. I know that in the real world you are supposed to have a resistor depending on the voltage supply. It does work great though. I carry it in my pocket all the time and don't even notice it. At night, it really lights up the way.

[urbosssez]

>.< cant wait for the laptop suitcase HURRY! please

[Firebert010]

Good 'Ible, however this has been done on this website countless times already. The variation you posted is nothing but a case mod to any of the hundreds of other LED flashlights here.

[nagutron]

Yeah, but using the CF card case is a good idea. I have dozens of those things around, and they're the perfect size.

[el eliel]

yeah, what he said. "think inside a DIFFERENT box".

[Instructabilis Deus]

Thanks Nagutron. Also, the size allowed me to use much larger batteries than the usual watch battery fare. I got these out of a crapped out wifi detector, which might have made a good flashlight candidate itself if I hadn't thrown the rest of it out like an idiot.

[el eliel]

i like. macguyver has nothing on this one. and, i was wondering why i was holding onto that sd case i never use...

[Instructabilis Deus]

"i was wondering why i was holding onto that sd case i never use..."

I like the way you think. ;⁾

[GorillazMiko]

That's actually pretty cool. I was thinking you could have the two batteries next to each other, and a wire connecting both of them together, with the leads of the LED on the batteries, that would come out nice. This is similar to my idea I was thinking of when I saw this Instructable... great job anyways! The last picture.... NO DEAL HOWIE! Looks like those cases.

[nf119]

Simple, Easy and Effective.

[joejoerowley]

Nice!