If you like making jewelry and have some experience using the Othermill, this is a great project for you! This style of necklace offers a wonderful way to get creative with double-sided machining on the Othermill.
The four LEDs on the back of the pendant provide a beautiful glow around the outline of the pendant and highlight the pattern on the front of the necklace by illuminating the etched traces.
This tutorial offers the design files for three different designs: a blank front, a circle design on the front, and the actual bird patterning on the front. Download these files in the next step!
Of course, feel free to use this technique to design your own pendants by mixing and matching your favorite shapes with your favorite-colored LEDs. If you do design your own unique necklace, please post pictures of it in the comments. All of us here at Other Machine Co. would love to see it!
Note: This is the first version of our Light-Up PCB Necklace. Check out V2 for an updated version.
Step 1: Tools, Materials, and Files
- Computer with Otherplan installed
- Flat end mills, 1/64" and 1/32"
- Soldering iron and solder
- Hotplate or toaster oven
- Solder paste
- Jewelry tweezers
- Needlenose pliers
- FR-1 board, single and/or double sided
- LEDs, surface-mount (4)
- Resistors, surface-mount, 43-ohm (4)
- Jewelry-making supplies:
- Jump rings
- Sterling silver or steel wire for wrapping. You can even use stripped hookup wire!
- Chain, Chord, and/or Beading thread
Note: All the materials listed above, with the exception of the tap and paste, are included in our handy Light-Up Necklace Kit.
- hummingBirdNoFront.brd single-sided hummingbird, no pattern
- circles.brd circle pattern for the front
- hummingBirdWithFront.brd double-sided pendent with bird pattern on front
- claspBoard.brd clasp
Step 2: A Note About Designing the Files
We've provided design files for you to use, but of course you could also design your own! You could start by finding an image to use as concept art, like the hummingbird picture from this site, and then head over to EAGLE.
If you don't know how to use EAGLE or need a refresher, check out our tutorial on designing circuits with EAGLE.
EAGLE makes it hard to trace or replicate outlines from images, so we ended up freehanding the humming bird outline. That board file is attached, though, so you don't have to!
To make our file, we made a simple schematic of 4 surface-mount (SMD) resistors and LEDs in parallel rather than in series. This allowed for each LED to have the full 3-volt drop across it, and it also means that the other LEDs keep working if one burns out. For a more detailed description of parallel and series circuits, check out this page.
Then we laid out the traces on the board (shown here) and added large pads on the head and wingtip to attach the mounting hardware for the chain/cord that will eventually complete the necklace and the circuit.
This necklace uses 43-ohm resistors, so with a voltage drop of ~2.5 volts across the LEDs and a 3-volt battery, that breaks down to ~10mA drawn from each LED. Therefore, the whole necklace draws about 40mA. Unfortunately, with a CR1025 battery, this necklace will only last for about an hour. Thankfully these batteries are pretty cheap!
If you want longer life out of your necklace, use bigger resistors or add a bigger battery. For instance, using 150-ohm resistors would make the necklace last for nearly 3 hours, but keep in mind that the LEDs will be much dimmer too. Using a bigger battery will increase the life of the necklace while keeping the LEDs bright but will require you to alter the clasp board to accommodate a different battery holder.
Step 3: Cut Out Your Necklace
Download the EAGLE board file of your choice and import it into Otherplan. If you need a refresher on cutting FR-1 boards with Otherplan and an Othermill, check out our Hello World tutorial.
These necklaces use a 1/64" flat end mill to cut out the traces, and the trace clearance was set to zero to speed up the cut time. Again to speed up the cut time, a 1/32" flat end mill was used to cut the outline. Increasing the end mill size not only allows you to increase the feed rate (the rate the end mill travels through the material), but it also allows each pass to cut deeper, which really makes the cuts faster when cutting outlines.
Note: If you're making one of the double-sided versions, make sure to use the double-sided alignment jig that came with your mill to line up both sides! Also make sure to choose the correct material in the Setup Material menu.
Step 4: Add Light
Now that you've got a board, it's time to add the surface-mount LEDs and resistors.
While it is possible to solder these puppies on with a traditional soldering iron and spool of solder, it's super hard and you might get pretty frustrated. The recommended technique is to use solder paste in a fine-tipped syringe and a hotplate or toaster-oven.
- First, place the components to make sure the pads line up.
- Then, double check the polarity of the LEDs with a multimeter by touching the LED leads with the red and black probes of the meter. If the meter is switched to the "continuity-checker" or "diode" setting, then the LED will light up if the leads have the right polarity.
- Remove the components, squeeze a small dab of solder paste on each pad, and place the components back on with tweezers.
Note: It's helpful to do all the placement of the components with the board right on the hotplate or toaster oven so you don't have to move it after!
- Once you're happy with the placement, turn on the hotplate to a 40% heat level, which should be around 420°F.
- It may take a bit of experimentation, but wait for several minutes for the solder paste to "flash" silver. Once that happens, quickly pull the board off the heat with tweezers and let it cool.
We left the first board on the heat for a bit too long, and as a result the plastic of the FR-1 board burned a bit. It actually looks pretty cool, because it provides a nice colored gradient across the front of the pendant. Sometimes mistakes make projects look better!
- Make attachments for the chain by using jump rings, or make some simple metal rings with stripped hookup wire and round jewelry pliers.
- Solder the rings to the pads you made on the head and wing of the bird.
- Now is a good time to test the LEDs to make sure they all light up. You can do this by touching the head and wing pads with the continuity checker on the multimeter.
If the LEDs all light up, great! If they don't, you'll have to debug the circuit further. Start by testing to see if the LEDs work individually, using the same method you used to check the LED polarity. If they all light up, then you may have put an LED in backwards, and you'll have to remove it and turn it around, then solder it back in place with a soldering iron. This type of replacement has to be done with a soldering iron and is a huge pain, so be sure to double check that the LEDs work and have the right polarity before you solder them on in the first place.
Step 5: Add the Battery Pack
The battery for the necklace rests on the back of your neck near the clasp, and the power for the circuit is carried through both sides of the chain or cord.
Download battery pack file. This file was also made using EAGLE, and it holds the 3-volt CR1025 battery and has 2 rings for the clasp to hook into. One ring completes the circuit while the other breaks it, allowing the wearer to choose whether to have the LEDs on or off.
Step 6: Complete the Necklace
There are a couple of ways to complete the necklace:
- Braid some fine wire in with black beading thread. Use the thread from the braid to tie to the pendant, clasp, and battery pack, and then complete the circuit with the wire. The thread provides the strength while the thin wire carries the current for the LEDs.
- Another option is to use the chain with or without a wire. Weaving a wire through the chain will provide more consistent power to the LEDs. The current can be carried through the links of the chain alone, but lighting the LEDs will just be a bit flaky.
Step 7: Wear It!
Wear your PCB necklace during the daytime with the clasp in the off position to conserve battery power, but at night switch it on to show off your awesome creation!