I had a couple of Altoids tins laying around and decided to make a Morse Code practice key. This is about the most simple electronics project you could get, but the end result is kind of fun.

Materials:

Altoids Tin - empty and wiped clean
Piezo Buzzer - 3v+ LED - optional
Small Gauge Wire - solid is easier to work with than stranded - I used a bit of thermostat wire
CR2032 Battery - or any other 3v battery
Foam - to build up a 'frame' inside the tin
A Momentary Switch - I used a spare Gateron key switch I had laying around
Styrene or Cardboard - to make the top cover you'll mount everything on
Binder Clip
Electrical Tape
Solder & Soldering Iron
Hot Glue Gun & Glue
Sandpaper
X-Acto/Hobby Knife

Step 1: Prepare Tin & Cut Foam

Using a flat-head screwdriver or a knife, carefully pry loose the hinges on the Altoids tin and remove the lid. You can push the hinges back closed again to give the tin a more finished/smoother look. We won't be using the lid.

Next, trace the outline of the tin onto your foam and cut it out. The foam should fit snugly inside the tin.

I got lucky that my foam was exactly the right height, but you may have to layer or trim it to make it the same height as the tin.

Step 2: Make Room for Everything

Using an x-acto knife, cut the foam all the way around the tin about 1/4in in from the edge. You want to cut almost, but not all the way through the foam. Then carefully remove the middle to make room for your electronics. Leave a thin layer of foam on the bottom of the tin as an insulator and to prevent shorts.

This doesn't have to be super smooth or perfect.

Step 3: Cut Out the Top Cover

Next, take your sheet of plastic or cardboard (plastic really does work better) and again trace the outline of the Altoids tin onto it. Then carefully cut it out.

Next, you'll need to do some sanding.

If you look closely, you'll notice that the Altoids tin has a tiny lip around the inside of it. You want to sand the top cover down just enough that you can snap it into place under that lop, but be careful not to remove so much that the cover is lose.

Both the tin and the plastic have a little give to them, so this isn't as difficult as it sounds. Just go slow and check the fit often.

Step 4: Cut Holes for Parts

Now it's time to cut holes in your cover so you can mount your hardware.

Place the Piezo buzzer on the cover where you would like it to be mounted and trace around it. Carefully cut out that circle.

If you're using an LED, put two small holes below that for the LED leads.

Finally, below that, cut a 14x14mm square hole to mount the switch, which should snap firmly into it when you're done.

Step 5: Wire It Up!

Finally, it's time to mount the hardware and wire everything up. I apologize for not getting better pictures of this, but essentially you first want to snap the switch into place, then insert the LED leads through the holes.

For the buzzer, I placed it in the hole so that the top of the buzzer was flush with the cover, then hot glued around the buzzer to hold it into place. This way it isn't sticking up, and it was just the easiest way to get everything level and firmly secured.

I also used a little hot glue around the LED leads to hold that in place.

Check out the wiring diagram to see how that's done. It's very simple - you want to create a basic circuit connecting the battery's positive lead to the positive lead on the LED and the buzzer, and its negative lead to the negative leads on the LED and buzzer.

It's essentially just a loop, but you're going to put the momentary switch in-line on the positive line so that the circuit is interrupted when the switch is open.

Solder the wires onto the switch, the LED, and the buzzer.

To create the battery clip, I took a small binder clip and covered the inside of it with electrical tape. Then I simply used that to clip the two leads to the battery and removed the steel wires from the binder clip to save space.

Step 6: Put It All Together

Finally, flip your cover over and insert it into the Altoids tin to conceal all of the electronics and finish up. Some of the foam on the side may get squished down, depending on how close your battery is to the edge of the tin, but that's OK. If anything, it will just help hold the battery secure and ensure a good connection.

If you find that the buzzer is annoyingly loud, you can cover it with a small piece of electrical tape to dampen the sound.

If, like me, you used a mechanical key switch, now's the time to add your keycap.