This is an instructable for one of those useful little LED light thingys that clip onto a key. They help you find keyholes in the dark, as well as being useful as a small torch. The advantage of this over a keyring torch is that you don't have to find it on your keyring; just squeeze the key and there is light, pointing in exactly the right direction! The main challenge of this project is size, shrinking everything down to a slim profile to fit on the body of a key is not easy.

Of course, you could just go to the shops and buy one of these, but where's the fun in that? Also, my version has a much brighter LED and a much longer battery life.

Ok, here's the shopping list

SuperBright White LED (Size isn't that important, I had some 1.8mm ones left over from the Lego flashlight)
Small switch (I used these)
Stripboard
PCB mount battery (I used CR2032 ones which could be considered a bit big, but will last practically forever)

I get parts from Spiratronics.com as they are a really cheap source. You probably have your own preferred retailer :) They are pretty common components.

What would an instructable be without tools? I used:

Soldering iron
Solder (natch.)
Helping Hand (shameless plug: How to make a Helping Hand)
X-acto saw
Breadboard (optional, see step 1)
Electrician's tape (to make a rudimentary casing, more on this later)

That's It! A very simple project, this one. Head to step 1 to get started!

Step 1: Circuit Diagram/Testing (optional)

Optional: I always like to test my components and circuit diagram on a Breadboard before I make anything, but you don't have to do this as there is a very low chance you will have got a broken component. The circuit diagram is very, very simple, the only confusion that may occur is that the switch has two sets of contacts.

The next bit is to test fit everything to the stripboard to find the smallest arrangement of the parts; I managed to get it down to a 30x30mm piece.

Step 2: Construction/Conclusion

Now to put it all together, permanently :)

First the stripboard needs to be cut down to the right size; use pretty much any tool you want, it's very easy to cut.

Soldering! This is easy, just make sure there are no dry joins and that you don't overheat the LED or the battery.

Lastly you need to put some sort of casing round it to stop it getting damaged. This needs to be something thin and light but also waterproof, especially if you live in England :P I used electrician's tape, but it's not a particularly elegant solution. If you can think of a better case, please put it in the comments as I would very much like to know! (I would only add it to this instructable with your permission and crediting you for the idea)

That's pretty much it! It turns on by pressing to top left hand corner and is very bright for its size; it measures just 30x30x8mm. Why would anyone want a shop-bought one?