Keychain Thumb-size Flashlight : Easy - Medium - Hard

You can find a lot of button cell battery flashlight on Instructables. They are cheap, as easy as plug n play and tada.. "illuminate". My project started when I saw my Daddy's driver having difficulty to plug the car key into the keyhole. Having a dark window films in a dark basement parking lot, should be no problem for what we do couples of time daily, yes, plug in the car key. But you know.. old man.. we will facing the same problem in the future :) There are a lot of commercial keychain flashlight at low price in bulk. But hey.. we are Makers, why don't we make one for almost free (my currency converter is showing USD 0.25 or IDR 3,500) ? And I only need one for we have only one car, so why should I buy 5? Here in this project, actually three projects, I will show you different approaches and all roads lead to Rome. Well, I have to admit that my previous words were wrong. Now I need one for the car, one for my everyday carry, one for my Dad, and everyone else who loves travelling with Led in his/her pocket :D

The main idea is how we turn it on/off without soldering a switch onto it. The circuit is simply a LED and a 3V coin battery (CR2025 or CR2032). We do not argue about resistor and lifetime of the battery or LED here. Make it as simple as : Turn on the light, plug the key, turn off the light. That's it. So I guess the battery will last long enough for this purpose. Now you can choose to do it the Easy way, the Medium way or the Hard way.

I will start with the Medium level which has a soft ON and this is my initial idea. Simple but one part needed may be difficult to find in local hardware stores.

As you can see in the photo :

• A LED (preferably white for better view). If you are going to buy 1, I think you can get it at 1 cent.
• A coin battery (CR2025 or CR2032). As low as 25 cents per unit.
• A large heat shrink tube. As large as the coin battery can get into it.
• Scissors.
• Pliers.

I hope you have met and known the basic of this famous semiconductor called LED. If you don't, please visit this instructables All You Need to Know About LEDs. There are basic information about the circuit and type of LEDs.

In short, I will tell you that LED has polarity. The larger piece inside the LED (shorter leg) is cathode, we put it at the bottom of the battery. The smaller piece inside (longer leg) is anode and connect it to the top side of battery. If you put it the wrong way, it will not illuminate.

Bend the end of the cathode leg with pliers into a circle shape with the overlapping part goes on top of the previous leg to get a better connection to the battery negative terminal (bottom).

Now bend the anode leg a little bit upward and then bend into a circle shape with the overlapping parts go to the bottom of its previous leg. You might want to make two or three turns. Refer to the photo for better explanation.

Using the battery container cardboard to cover the battery side (top) to prevent direct connection to LED's anode pin. This is how we put the flashlight initially OFF. Fold the cardboard at least two times (or three times max) on top of the battery. Do not fold it too thick because your anode pin might not touch the battery positive terminal while pressing. Better put the cardboard near the circles we made on the pin because the LED's legs are soft. Several pressing on the leg will cause a permanent downward bent and put the pin touching the battery terminal forever. If so, you are losing your flashlight switch.

Put them all (the battery and LED) into the large heat shrink tube and start heating them up. For a very large shrink tube, the opening side will not well stick to the LED. Instead you will have hollow around the LED, you can fill it up with hot glue or anything else, it doesn't matter. As long as the body part are shrunk well, you will have your thumb-size momentary switch flashlight working good. All you need to remember is the position of the unseen button :D

Use a large needle and make a hole on one corner of the shrink tube to hook it on your car keychain. Now there should be no more difficulties for my Daddy's driver to plug the key ;)

Well some of you may find it difficult to get a large size heat shrink tube at local electronic stores. Then you can pick the easy mode of having a thumb-size flashlight. All you need is a LED, a brand new coin battery (with its packaging) and a large needle (for better result). You see that we have spaces one millimeter or two inside the battery packaging.

Use a needle to make holes on top of the battery, 5 millimeters wide on the center. So your needle goes down around 2.5mm from the center and then goes up after 5mm travelling inside the packaging.

Now make holes through the bottom of the battery.

Bend one leg of the LED to the right and the other leg to the left to avoid stabbing into our hands or legs in the pockets.

Give it a press on the battery and let the LED lights up your days ^_^

The last thing you need to do is punch a hole on one corner and put a key ring through it.

Now I am addicted to woodworking :D Get a piece of plywood that is thick enough to put the coin battery inside. I cut them into the size of 3 x 5 cm. So I get a three layers wafers with total 5 mm thickness.

• Split one layer off.
• Draw the LED and battery positions on it and cut them out so that we can put those parts in.
• Put the LED in with cathode pin (short one) on the bottom.
• Put the battery in.
• Put a piece of cardboard on top of the battery covering 2/3 of the battery.
• Now the split off layer of plywood is thin enough and fragile. So I cut a piece of cardboard to give it a raise instead of cutting the bottom layer deeper (which is also risky of breaking the bottom ply).
• Initially I decided to drill four holes on every corner then put bamboo chopsticks in it as dowels. This way I can replace the battery by breaking the dowels and replacing the new dowels in. But I was too excited to get it done, I continued this project at home and I had no drill at hand. So I later decided to glue them all.
• Filing the sharp edges and we are done.

One might think that "Wait a minute, this is wood and you just cannot press it." Says who? Plywood is soft wood, as I mention before when I split the top layer off, it is very fragile. You can bend it, you can tear it. So that thin top layer is soft enough to press ^_^

I later drilled a hole on one corner to put the key ring.

Wooden keychain be mine. I love the simple rectangle shape with no sharp edges, the wafers, and mostly tough to be one of my EDC (everyday carry).

The shrink tube version is solid enough and fit in the car keychain. It has a soft built-in momentary switch.

The battery packaging version is the most simple to make, yet has a stable soft built-in momentary switch. The packaging plastic can hold the pin well on its OFF position. It won't touch the battery positive terminal without a certain pressure. It doesn't look so bad either. I can show it off to the kids or the family members who need some light in the dark :D