The bracelet has a wood base (plywood, specifically), a veneered outside, a channel for an LED circuit and diffusing resin, and a leather lining/battery cover.
Most of the steps don't take much time, but the drying between steps does. You won't be wearing this the day you start working on it so plan ahead.
By the way - ash trees are absolutely beautiful and in big trouble, at least in the US. Read this over help out some lovely trees!
Step 1: Materials and Equipment
Wood Veneer - make it something special, this is a great chance to use something really exotic. My olive ash piece had a really great pattern. It needs to be just a straight piece of veneer, none of that paper backed stuff they sell at home improvement stores. A 2x12" piece should get the job done.
Wood Base Material - I had 1/8" thick plywood laser cut to build the backing of the bracelet out of. If you do any woodworking you almost certainly have a better selection of tools to work with so you can probably make this with a jigsaw, bandsaw, router or some other clever way. The upside to lasering is that I was able to make parts for another project from the pieces cut out of the bracelet and I was able to be super precise.
LEDs - I used the impossibly tiny surface mount style so that I could keep the channel as narrow as possible. I didn't want a big, bulky bracelet. If you're willing to go with a bigger bracelet you can use much larger/friendlier LEDs. Mouser #630-ASMT-TWBM-NT902
Resistors - One per LED, use a handy calculator to get the right kind. Mouser #299-150-RC
Battery Holder - This needs to hold 2 coin cell batteries. Mouser #122-2820-GR
Coin Cell Batteries - I used CR2016 batteries because they're only 1.6mm thick and took up a small amount of space. Mouser #658-CR2016
Resin - A two part epoxy resin is ideal for this. You can get away with the table top stuff if your channel is thin, but a casting resin is better.
Resin Dye - I used a small amount of white resin dye to help diffuse the light.
Wire, Solder - Use this to connect the LEDs and resistors to the battery case. Lead free is best, but I prefer solder with lead. There are really only two tiny areas that they lead might be accessible, and you'd probably die from ingesting all that resin, wood and varnish before the lead got you. I stripped the insulation off of some stranded copper, solid would have been a lot easier.
Wood Glue - To glue the wood together. Keep it closed and keep the nozzle clean so you don't have to fight dried bits.
Barge Cement - To glue the leather to the wood.
Rubber Cement - To temporarily tack parts together.
Super Glue - To quickly stick the circuit to the bracelet. It only needs to hold until the resin gets in there.
Clasp or Closure - This will close the leather over the battery pack. I used two small snaps.
Sturdy Needle and Thread - To sew on the snaps onto the leather.
Wood Finish - Some sort of varnish to go over the whole thing with. I like water based varnish. I'm sure you have a favorite.
Leather - This will line the bracelet. I used some factory scrap from an outlet. Consider what color will look good and what will feel nice on your skin. Thinner is better.
Soldering Iron/Solder Sucker/Sponge - To solder the electronic goodness together. WIth a little luck/skill you won't need the solder sucker.
All the Small Clamps In the World - You're going to be forming wood veneer. More clamps equals more likely success. The cheap brightly colored plastic style will get the job done, no need to pay up if you don't already have some. I've picked up tubes of a dozen or more for a couple bucks before and they're endlessly handy.
Resin Mixing Gear - Paper cups and popsicle sticks for easy mixing and pouring.
Scissors and/or a Utility Knife - To cut the veneer.
Container for Soaking Wood - This isn't for food anymore, and it can take some heat.
A Way to Heat Water - I have a handy electric skillet for this, pick your favorite. Hot tap water was enough to soften my veneer, but you might need more heat.
Gloves, Dust Mask, Safety Glasses - Don't play too cool for this stuff. Resin can have permanent affects on your skin. You don't want a piece of flying shrapnel to be the last thing you ever see. Dust can have lasting consequences in your lungs. Don't say I didn't warn you.
A Way To Drill Two Small Holes - I used my Dremel with a 1/16" drill bit.
A Way To Cut Wood - I had my parts laser cut because I lack the equipment to do it at home, but if you can do it with your equipment then, by all means, do.
Sand Paper - A nice range of papers is best. The finer you go the nicer your bracelet will be.
Masking Tape - Useful for taping over places that resin might seep through.
Standard Household Items - Paper towels, typing paper, other ordinary stuff you probably have.
Step 2: Bracelet Base
If you're unsure about the inner bracelet dimension start out with measuring any that you might already have. I did that, drew up my plan, then printed it onto cardstock and cut it out to check that my hand went through. Make sure to plan some space for the leather lining, too.
If you're using a stack of cut plywood like this, glue them together and sand them smooth. Don't glue the top or bottom piece on just yet.
Step 3: Bending the Veneer
Measure how large the outside of the bracelet needs to be. Add at least 1/4" to the width of the veneer and about an inch to the length. You may want to add more if your wood seems prone to chipping. Mine was very prone to chipping.
Put masking tape over the place you'll be cutting your veneer. This helps stabilize it and reduces that chipping risk. Mark out your cutting lines. I cut mine with ordinary scissors, "cut a penny" scissors would have been better. A utility knife would also work. Once your piece is cut out gently remove the masking tape.
Soak the veneer in water. I started with hot tap water and my veneer was completely limp in about 10 minutes. Yours might take more effort - more time or heat should help. Trees vary a lot so you'll have to use your best judgement here.
When the veneer is very pliable pull it out of the water, dry it a bit and then get ready to wrap it around the base. Start with one end on the block of wood where the battery pack goes. Clamp it down securely. Then work the wood around the form, clamping as you go. You want a neat, even curve. Don't use any glue. Clamp until you get to the end, leave the tail hanging out. Let this dry thoroughly.
Once it's completely dry (we're talking hours or overnight), unclamp it, gently remove it from the form and set it somewhere safe. It would be really easy to crush it right now, so up high, out of the way, where it won't fall is best. Remove the top and bottom of the bracelet and scrape off any residual rubber cement.
Step 4: Adding LEDs
Cut a strip of paper the same width and length as the channel in the bracelet. I folded in half and half and so on to distribute my LEDs. Mark where each one goes. I decided to run two positive leads - one at the top and one at the bottom, and one negative/ground lead - mostly made of resistors down the center.
Use a bit of rubber cement to glue each LED face down on the template. Check, check and check again that the polarity is correct. These tiny LEDs don't take too much abuse so if you have to unsolder them they might not resolder and work.
Step 5: Assemble the Electroincs
Find some time when you're not busy or stressed. Don't drink coffee or any energy drink, you can't afford to be jittery. Focus on doing this because it's very tiny and relatively difficult.
Solder a wire across the positives of each side. Leave extra wire at the ends. I used masking tape and helping hands to hold the wire where I wanted it. If you're not experienced with soldering read some instructables on it - you want to heat the wire and contacts, then add the solder so that the pieces are firmly attached.
Bend the resistors to fit the template. Solder your resistors on the other side of the LEDs, I just sort arranged them in sort of a herringbone down the center. Trim any extra resistor wire (except at the end.) Make sure all of the resistors are firmly soldered together.
*Use some masking tape, a couple pieces of wire and a couple batteries to make a tester. Check that everything is working as often as you like. I checked after every LED or two was soldered in. The earlier you find a problem the easier it is to fix it.*
Step 6: Attach the LEDs to the Bracelet
Drill a small hole to the area the battery holder will go in on each side. Centered on the height of the bracelet is best, you want the wires to go through that hole and right onto the battery pack contacts.
Slide the resistor end lead into one of those holes (solder on more wire if it won't reach.)
Use the super glue to carefully glue each LED to the wood. Gently peel the paper off after the glue is set. Run the two positive leads through the hole at the other end. I ended up gluing, peeling and clamping each LED/resistor combo. I left it like that until they were dry. I also took advantage of all those clamps to make any wire bend adjustments to keep the wiring as tight to the wood as possible.
Let this all dry like you mean it. Overnight would be super.
Step 7: Adding the Battery Holder
Solder the positive and negative leads to the positive and negative contacts on the battery holder. This will be fairly difficult because of the limited space. If your soldering iron came with a long narrow tip this is the time to break it out. My battery pack had a large space for soldering so I was able to make a pretty big connection. This soldering is the most likely to take abuse when the bracelet is worn so do your best work here.
Step 8: Check That Everything Is Working
Also, take this opportunity to check out all of the wiring, clean up any little solder lumps, trim any remaining unnecessary wires, etc. The cleaner and neater your wiring is the better your finished project will be.
Step 9: Gluing in the Veneer
Glue one end of the veneer onto the block of wood where the batter pack sits. Clamp this well and let it dry.
Once dry, sand it so that it's completely tapered and there's no hard edge to the veneer. You do this so that there isn't a bump where the other end of the veneer overlaps. You could just trim the veneer so that the ends push up against each other, but I liked the smooth blend effect better because of the bold grain I was using.
Glue the veneer around the end cap edge, applying glue and clamping neatly. You want this to seal well and look smooth. This will all seat together better if you add the other end cap (without gluing it in place). It will help keep the veneer square and even. At the other end glue the veneer down over the tapered area and let the rest remain unglued. You'll trim it later. Again, let this all dry thoroughly.
Step 10: Filling With Resin
Resin shrinks. This is terribly inconvenient in this situation, so we need to outsmart it. Depending on your resin, this shrinkage can be 10% (and probably even more.) If you fill the channel completely you risk collapsing the veneer or dislodging the electronics, both of which would be a total bummer after all this work. If you filled 10% of the channel at one time and that shrunk 10%, that would only be 1% of the total volume of the channel, and basically have no effect on the finished piece. Each subsequent 10% fill would fill that 1% from the previous fill. Unless you're making about 100 of these this is impractical, as it's hard to mix that tiny amount of resin well and each layer takes about 24 hours to set up, meaning you'd spend 10 days filling the bracelet.
My resolution was to mix my resin, fill the channel about halfway, and tilt it around to cover as much of the sides of the channel as possible. The channel is half filled, but the thin layers on the sides have much less of a shrinking problem than a block would. If your bracelet has a larger channel you may want to do three or four layers, better safe than sorry. I tinted my resin with a tiny amount of white dye (easy to get at most craft stores that sell resin). By tiny I mean less than a drop. I used a toothpick to pick up a little dye and mixed it in. You can always add more. You're looking for cloudy, not white. Stir your resin really, really well. Let it sit for a moment, then breath over the top of it to help break the bubbles coming to the surface. Pour it in a tiny bit into the channel at a time, letting it run down to the bottom. Do your best to keep the resin off the veneer and the core of the bracelet. After filling it halfway you'll want to pop the other endcap into place to make sure the resin sets up in a way that lets the veneer stay nice and square. If you get resin onto anything that touches the endcap make sure to put waxed paper between the two - that will let them separate later.
After the first pour of resin sets up you're ready to finish it up. This time fill the rest of the channel, and smear the resin onto the bracelet core and the inside of the veneer. Pop that other endcap in and let it glue into place with the hardening resin. The resin shrinkage works for you this time, helping to pull that endcap in really tightly. Wipe any extra resin off with a paper towel while it's still liquid. (Obviously make sure you push the cap in as well as you can, and clamp it if it won't settle in well on it's own.) Let this all set up completely before continuing.
Step 11: Trimming the Veneer
Sand this end down to a taper as well. The idea is to have a seamlessly round bracelet. Take your time here for a nice finish.
Also trim and sand any veneer that's past the edges of the bracelet.
Sand the whole thing until it's smooth to the touch. It's for wearing, the finishing time is worth it.
Step 12: Varnish
Step 13: Prepare the Leather Lining
Cut a strip of leather about 1/4" wider than the bracelet and a couple inches longer than the inside circumference.
Use a razor blade/utility knife to very carefully thin the leather at one end.
Sew the male side of two small snaps onto this end, keeping in mind that the leather will be narrower when the bracelet is finished. Use as many stitches as you can through the fewest number of holes possible. More perforations make it easier for the leather to weaken and tear.
Place the leather where it will go on the bracelet and clip it into place. You want to have the leather cover the batteries tightly. At this end the leather will fold over and the snaps will be attached to the underside. This will keep the stitching glued down and concealed. You can double up the whole length of the battery pack if you'd like. That's what I did.
Press the leather down on the snaps to mark where the other side should go. Remove the leather from the bracelet. Thin the leather like you did on the other end and sew in the other side of the snaps. Use the barge cement to glue this folded over part to itself.
Thin the long edges of the leather as much as possible. Be careful to not cut all the way through. You're doing this so that the leather will meet the edges of the wood smoothly.
Step 14: Glue the Leather in Place
You really only have one chance to get this right. Place the leather exactly where you want it. This is why it was cut wider than the finished bracelet, once it's glued into place you can trim the extra with a very sharp utility knife blade.