Glowing Laser Cut Pendant With Magnetic Battery Holder

After trying out various designs over the last couple of months (check out my other Instructables), I finally came up with this one. Inspired by the Led Earring instructable, I ended up using magnets to hold a coin cell battery and act as contacts for the LED. The cool part is that the battery actually serves as a switch - slide it up to turn on the light, push it down to turn it off. And as a bonus - you do not need a screwdriver to pull out the battery (as opposed to SMD battery holders).

I made about 15 such pendants and gifted them in the last Burning Man (2013). It was a blast :)

Short warning - I did not have direct access to a laser cutter at the time, so this design is not perfect. You'll need to make small adjustments to the parts you cut, so make some extra parts. Just in case.

Also, note that the pendant is asymmetrical.So make sure you align all the parts properly before cutting and gluing. I guess next time I should add "up" and "down" engravings on the pieces themselves.

On/Off:

And again:

Changing colors:

You'll need the following:

• 5mm slow flashing LED. Or a fast flashing LED, it's up to you
• 3mm Plywood sheet
• 1mm clear or "frosty" acrylic. 1.5 and 2mm should be OK too - as you'll see later on, we make several layers anyway
• CR2032 battery
• Two M2 (or is it 2M ) screws, 16mm long
• One 1/4" x 1/8" x 1/8" Block Neodymium Magnet N45 (or stronger). Try here - http://www.kjmagnetics.com/
• Two 3mm x 5mm Cylinder Neodymium Rare Earth Magnets N45 (or stronger). Try here - http://www.kjmagnetics.com/
• 400 grit sandpaper (to make clear acrylic look "frosty")
• Epoxy glue
• Superglue with a small tip
• Optional - conductive glue (you'll see why)

If you decide to go for different magnets (for example, the slightly smaller 6x6x3mm block magnet), don't forget to change to the design accordingly.

Below you can find the design as DXF and as PDF files. Make sure you used the right material for each file.
Files are now also available in SVG format.

This is just a short step to make sure you understand the different parts. Note that in the photo, all the acrylic parts will have the thin plastic films on. I left them there so it's easier to see on the photo, but do remember to remove them (I forgot once..)

• The plywood piece with the "man" figure is the front
• The other plywood piece is the back part. It will hold the block magnet
• One acrylic piece will serve as a diffuser
• The acrylic piece with the two larger holes will hold the cylinder shaped magnets. I'll refer to it as the battery holder
• The other acrylic parts are spacers. They'll be placed between the front and back of the pendent, and will hide the LED. Note that some spacers are "chomped". This will allow you to add a ring for a chain later on. I'll futher explain this on the next steps.

First, we want to place the rectangle/block magnet in the rectangular groove of the Plywood back piece. Use a scalpel to carefully enlarge if needed, but don't make it too big - we need a tight fit here. When you place the magnet, align it so about 1mm sticks out pointing down and the rest points up.

What's up and what's down? That is kinda confusing (so make sure you get it right!). "Down" is where side where the pendant meets your chest. "Up" is the side that points to the front piece (with the "Man" figure). The reason why you want it to stick out a little bit is because the battery is slightly ticker than the plywood we are using, and allowing the magnet to stick out a bit will help it holder the battery better. Just make sure you align the front and back pieces (have I mentioned that the design is asymmetrical?).

Now let's prepare the LED. First, Remove the LED’s "skirt" (cut it or use sandpaper) - this will make the LED slightly smaller, and will shave off ~1mm from the height of the pendant. Next, we want to bend the anode (+), which is typically the longer terminal, make a U shape, and place it between the block magnet and the plywood. It's hard to explain, so I hope that the images are informative enough (let me know if they aren't). 

Careful! The LED terminals are fragile. You can only bend them ~3-4 times before they break (you might need some extra LEDs..).

Make sure is that the magnet actually touches the anode, and apply some epoxy glue around the magnet of the upper side of the plywood piece. Important notes:

• Do not use super glue here. Super glue tends to coat everything, and it will get between the anode and the magnet
• Make sure that LED terminal touches the magnet
• Do not put any glue between the LED and the magnet

Why not just solder the LED to the magnet? Heating the magnets will cause them to lose their magnetism (and we don't want that, do we?)

Next, we are going to place the two cylinder shaped magnets in the in the acrylic battery holder piece. The magnets should fit snugly in the holes... but then again, they might not. Whatever you do, do not try to force them in. Acrylic is not flexible, and it will just crack. If he holes are too small, carefully enlarge them. You can either by re-cutting the shapes, use a drill, or just use knife and rotate it inside the holes to enlarge them. Don't make them too big though, we still want them to hold the magnets.

Place the magnets so about 1mm sticks "down" (this side will hold the battery). Make sure all the pieces are aligned, and then put some epoxy around the sides of the magnets, on the "top" side of the acrylic battery holder (aka - not the side that holds the battery). Be careful not to cover the top part of the magnets - we need to keep them conductive. Do not use superglue.

Now take the back piece (from the previous step) and carefully slide the LED through the hole in the acrylic piece (as shown in the last picture). Use a knife to remove any excess epoxy that interferes with the alignment of the two pieces. Then, bend the cathode (-) of the LED so it touches one of the cylindrical magnets. 

Now is a good time to hold the pieces together and test the contacts using a battery. The LED should light up.

Optional – to improve the contacts, put some conductive glue on the LED terminals, where they touch the magnets. Let it dry before proceeding to the next step.

Use the sandpaper on both sides of the diffuser acrylic piece to give it an "icy" look. If you aren't sure which piece is the diffuser, check step 2.

Place the pieces in the following order (top-down):
* Front plywood piece (the one with the "man")
* diffuser
* 2 x long spacers (the pieces with two screw holes)
* 2 x short spacers (the pieces with one hole)
* battery holder + back plywood piece

The next part is a bit tricky, and sadly I don't have photos showing it. The goal here is to glue the short spacers to the long spacers so they don't move. Put one screw all the way in the lower hole (the wider end of the rhombus) - it will help you align all the pieces before gluing them. Then, rotate the front plywood piece and diffuser sideways to allow access to the spacers. Put a drop or two of superglue and let it dry.

Rotate the diffuser and front piece back into position and close the pendant with the second screw. If the screws are too long, just chomp them with a wire cutter or a hacksaw. 

Place the battery in, and you're good to go!

Feel free to experiment with different sizes of LEDs. I actually ended up using two 3mm LEDs in some of the pendants, and really liked the result - smaller LEDs means fewer spacers and a smaller pendant.