# LED Circuit Pendant

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I've been thinking about entering the LED contest but couldn't think of an entry. I have a major problem when it comes to the LED contest...  My electronics skills are fairly rudimentary. I know how to use a soldering iron and I can identify the basic components but don't ask me to design a circuit or, for the most part, understand how to modify circuits. I was looking over the open contests and when I was checking out the Jewelry contest, the idea for making a pendant with LEDs popped into my mind. Instead of just putting LEDs into a design on the pendant, I thought it might be more interesting to make the circuit itself part of the design. Thus was born this instructable for a flashing LED pendant.

A couple notes before beginning:
1. The knowledge and items in this instructable are fairly basic. This is a limit of my current skills and tools/equipment on hand. On the upside, this means that anyone with basic skills and equipment can make the pendant.
2. I don't work on jewelry either by trade or hobby so my skills with the decorative wirework is poor at best. Hopefully, anyone making use of this tutorial will have better skills than me in this regard.

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## Step 1: Parts and Equipment

I've broken down the items needed into a few sections: the circuit, the pendant, and decorative touches.

Here's what you'll need for the circuit:
2x - 1K Resistor (1/4W)
1x - 1µF Electrolytic Capacitor (63V)
1x - 470K Resistor (1/4W)
4x - LED (Red)
1x - NE555 Bipolar Timer
Power source (not shown)
Switch (not shown)
Soldering iron
Solder
Wire
Hacksaw (not shown)

Note that a 1µF 50V capacitor also works. However, at the electronics store I purchased parts from, the 50V capacitor was black and the 63V one was blue. The resistors were also blue so I went with the 63V capacitor for aesthetic reasons. The colour of the LEDs should also be chosen according to your aesthetic tastes. I didn't list a specific power source or switch here. These parts can be worked into the design or hidden so the exact parts used can be varied according to your needs. I've tested the circuit and confirmed that it works with a 6V battery (one designed for headlamps), a standard 9V battery, and a 12V combo (four 3V batteries).

For creating the pendant, you'll need the following:

1x - Casting mold(s)
1x - Resin (polyester resin is shown but epoxy resin is probably a better choice)
1x - Catalyst
1x - Mixing cup
- Resin colouring (Optional)
1x - Mixing stick (not shown - I used a disposable wooden chopstick)
Craft foam
Glue gun

For decorative touches, I used the following:

18 gauge aluminum jewelry wire
Bent nose pliers
Side cutter
Scotch tape (not shown)
Heat shrink tubing, 16mm diameter (not shown)
Heat gun (not shown)

## Step 2: Prepare the Circuit Board

Using the mold as a guide, mark off the desired size and use the hacksaw to cut to size. The size shown marked off is 13x10 (in terms of available holes). This was cut down to 12x9. I had two problems with the 13x10 circuit board. The first problem was the board needed to be 13x9 to fit within the mold. The second problem was purely aesthetic - I wanted the 555 timer to be dead center and a width of 13 was slightly off-center so I cut the width down to 12.

After cutting the board, sand the edges and corners to remove anything that might result in injury.

## Step 3: Add the Circuit Components

The circuit is based on the one at http://www.555-timer-circuits.com/flashing-led.html. The only significant change I've made is to add LEDs (in parallel).  Add the circuit components to the board and solder in place. Add the smallest (in terms of height from the board) components first. With the components I had, that meant the 1K resistors first, then the 555 timer, then the capacitor, and finally the LEDs. The long prong of the LEDs goes on the outside track.

Important note: Do not trim (or leave a fair bit after trimming) after soldering the components in place - we'll need to attach wires to the protruding metal.
Also note the layout in the first image is the back of the board (i.e. what you'll be seeing when soldering).

## Step 4: Add the Wiring

This will by far be the most annoying and delicate part of the operation. It'll take a lot of patience, delicate work, and time. We need to create and connect the wires for the circuit. The first image shows a rough diagram of the wiring I planned to use. I started by creating the correct length wires to attach the LEDs. The ends of the wires are bent like hooks to snag onto the ends of the circuit components (which is why they should not be trimmed yet). The other wires I created as I went. Once the wires are all soldered in place, test the circuit and make sure it works. If it works, trim the protruding wires.

The main annoyances at this stage were: 1. The time it took to create wires of the correct size and 2. when soldering the wires, the other end often heated up enough to melt the solder and loosen up. There are that might have helped draw the heat before it traveled further down the wire but I didn't have any on hand.

## Step 5: Embed in Resin

Use the measuring cup to mix up 1 ounce of resin, following the instructions for the chosen resin. I added 2 ounces of resin to the cup (which was overkill - for a single pendant, it'll require less than 1 ounce). Then I added in the transparent dye (8 drops). The colour shown is actually darker than than the final result - the depth of the resin in the cup (almost 1") was a lot higher than the depth of the mold (3/8") so keep this in mind when checking the colour. I made sure the colour was mixed in (using slow strokes to avoid creating too many air bubbles).

Then I added the catalyst and mixed it in. Pour the mixture into the mold and add the circuit. When hardened, the resin will shrink so make sure the mold is as full as it can be. You may want to use a syringe (the ones you find at art shops, not medical syringes) to top off the mixture. If you do, make sure it's disposable, as it'll probably be clogged with resin afterwards. You'll probably need to add a weight on top to keep the circuit in place (the wires hanging off the side tended to drag that end down, lifting the other end. A 9V battery works well for this.

Put the mold in a well ventilated place and let it cure. The curing time is dependent on the resin you use, ambient temperature, the thickness of the cast, and the amount of catalyst that was added. Typically, you should let it sit for a few days before removing it from the mold.

IMPORTANT: Polyester resin produces harmful fumes. If possible, let it cure outdoors so you are not exposed to the fumes. Failing that, place it in a room with a ventilation fan that pumps the air outside. Epoxy resin is supposed to be much less toxic in terms of fumes so it is probably a much better choice. The only reason I used polyester resin was I had some on hand. If you don't have either, look into epoxy resin.

## Step 6: Add the Backing

Cut out small section of the craft foam. Trim the corners if desired. Position the wires going out to the power supply as desired. Using a glue gun, drop copious amounts of hot glue onto the back of the circuit. Press the craft foam into the glue and let dry. I suggest using a lot of glue because that will help hold the wires in place and reduce the risk of wires snapping off at the solder joints.  Once the glue sets, remove the pendant from the mold.

## Step 7: Add a Wire Frame

Adding a wire frame serves two purposes: 1. Additional decorative touches and 2. creates a way to attach the pendant to chains, backings, etc.  I decided on a simple wire frame that would include a couple loops to allow attaching a chain. Using the jewelry wire, create a loop. I held the wire near one end with the bent nose pliers, twisted the short end around the end of the pliers, then wrapped the short end around the wire.  Then I twisted the wire around the pendant and created another loop.  As mentioned before, my jewelry skills are poor at best so with skill or time and patience, you'll be able to do a much better job than what you see here.

I then attached the chain and looped the power wires through the chain (every 5th link). This configuration assumes that the power source will be attached at the back, where it's out of sight. To attach the chain, I first detached a couple links. To do this, I closed the bent nose pliers and inserted the end into the final link in the chain. I pressed my fingertip to the end of the pliers, essentially pressing the link down onto the pliers. Then, I slowly opened the pliers. This pushed the chain link open. Repeat and you'll have two open links. Attach the chain to the loops on the pendant with the open links and use pliers to close the links.

## Step 8: Add a Power Source

I decided to add the power source to the pendant rather than have it hidden around the back. To accomplish this, I used 4 small 3V batteries similar to watch batteries. First I prepared the wires by stripping the ends and forming loops with the exposed wire. Next, I stacked the batteries (all with the same orientation) and taped the side to keep them in place. I then made a couple cuts in the tape (one for each wire) to allow the wire through and placed red wire loop touching the top of the battery stack and the black wire loop touching the base. I then folded down the tape to keep both loops in place. Test that the battery stack works with the circuit. To improve the look of this configuration, I cut a piece of heat shrink, fed the wire/battery combo through it until the batteries were centered in the strip. Quick work with the heat gun and the batteries were firmly in place. Check the circuit using the power source just to double-check. The ends were then cut to match.

## Step 9: Attach the Power Source

I removed the wires from the chain and pushed them under some of the wire frame to keep them in place. I then used additional jewelry wire to attach the power source to the pendant. A bit of soldering to connect the wires and add a switch, and the pendant was done.

The wire work in step 3 can be greatly reduced if you have or have access to circuit board etching equipment.
Heat shrink tubing comes in different colours. I recall seeing black, white, green, red, and yellow. I'm sure there were other colours as well. I'm not sure how receptive it is to paint.
One thing I pondered was cutting a hole in the heat shrink to expose the center of the battery top (which was one reason to use a wire loop) but I didn't have anything that would give me a clean circle so that idea was abandoned.
I have all the components flush against the board.  However, they can be pushed higher if you want them closer to the front of the pendant.
- Add the LEDs after the resin step. The LEDs can be soldered onto the board after the resin has cured. This will allow the LEDs to protrude from edge of the pendant.
- Break up the circuit into several different components, embedding each in its own resin mold, connected via wires. This is useful for larger circuits or if you want multiple small pieces.

Edited to add schematics.  These schematics are assuming you're creating a 2 layer board.  These are based on the wiring in step 4 (photo 2).  I've added a couple spots for attaching wires for power (labeled with "+" and "-").  If these are used, the wires will be visible in the resin.  If you don't use these holes, just attach the power wires to the back of the board using the leads of the components as done in the instructable.

NOTE: These schematics are untested.  I have not created boards using these schematics so I can't guarantee they'll work.

Finalist in the
LED Contest

First Prize in the
Dremel Jewelry Contest

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## 20 Discussions

I only did the version in the instructable and didn't proceed further with this project so I don't have a schematic I've actually used for a custom board. I've added some diagrams for a possible schematic based on the second image for Step 4 (the wiring diagram). Given how some of the wires cross, it's assumed that a 2 layer board is used. Alternatively, you could do a single layer and the remainder in wiring. The diagrams are in the last step. Hope this helps.

I haven't actually created a board from these diagrams so it's possible that I've made a mistake. Double-check my work (cross-reference with Step 4, second photo).

If you create boards with the diagrams, let me know if they worked properly or if I've made a mistake.

If you wanted to make it look a bit fancier (not protoboard,) you can get boards fabbed for ridiculously cheap now. Eagle Layout is free to use for small (up to 8x10 cm) 2-layer layouts and is pretty easy to use. iteadstudio has board fabbing for as little as \$10 for 10 boards (plus \$5 or so shipping, max 5x5 cm.)

2 replies

Great suggestion. I didn't realize custom boards were so cheap. The pendant I created has a board size of roughly 3.3x2.5 cm so a 5x5 cm board would only yield a couple pieces. Of course, depending on the circuit , components, and the resin mold(s) you choose, the number of circuits you can fit on the board will vary.

One thing to note about Eagle Layout is it's free for non-profit use or evaluation only. So, if you decide you're going to sell what you make, you're legally obligated to purchase the software rather than use the freeware version. The Light version (functionally identical to the freeware version) is only \$49 so it won't be a huge financial burden to purchase it.

That particular place doesn't allow panelizing, so each board would hold 1 circuit. They only come out to around \$1.50 each though, so it's still pretty inexpensive.

Why not use naturally blinking LEDs? Then you could avoid all the 555 timer stuff.

Also, instead of making them blink, why not make them fade? Then you could have pulsing LEDs. If you're going through all the 555 trouble then doing a 555 fader circuit would be only slightly more complicated.

Awesome design though. I may be attempting something very similar this week.

5 replies

Thanks for the compliment. For this design, I was primarily focused on the look of the circuit/LED combo. I didn't use the naturally blinking LEDs because I wanted the circuit to be a major part of the design (from a visual standpoint). If I used naturally blinking LEDs, I wouldn't have had much to embed in the resin other than the LEDs and the power source.
As for using a fader circuit, there were two reasons I didn't use one:
1. The blinker circuit was simpler, which really helped with the wiring.
2. I liked the look of having the 555 surrounded by 3 resistors and a capacitor better than the components for the fader circuit.

If you attempt something similar, you'll have to let me know how it turns out.

Ahhhh, very good reasons.

I love the simplicity of the 555 timer. It has so many uses, especially with LEDs.

I guess if you wanted to use naturally blinking LEDs you could always just embed other items in there for "looks." Sure, it would be kind of cheating, but it would also save a whole lot of time and effort. (If you were to sell these on etsy.com for instance and needed to cut down production time.)

I'm going to try and make a fader LED necklace for a friend of mine. I'll post a guide on it when I do.

Thanks for the great guide! I voted! Hope you win!

I've never used a circuit with multiple naturally blinking LEDs but if you power it off, wait a few seconds, and turn it back on, it may be synced again. With some testing, you could get some that don't get out of sync too easily.

And as JoshuaZimmerman mentioned, it all depends on whether or not you want them to be in sync or not. If you choose LEDs that easily get out of sync, it would look somewhat random and slowly change pattern over time, making it a bit more dynamic.

Probably. Depends on the look you're going for. You could just include a bunch of LEDs and have them all blink randomly.

I was mainly pointing out how you could make it a lot more simple. Not better (as the 555 timer route is heaps better), just more simple. In case someone who isn't very good at all this electrical stuff wanted to make something similar.

I personally am going to try making this but with a couple of fading LEDs.

You have a nice ideea with this pendant. Let me tell you some improuvements :
Instead of using a 555 timer, try yo use a microcontroller like pic12f508 ( chose the smd package) instead of using wires you can make a diy pcb . Instructables have a lot of documentation about this. Use a double layer pcb and use smd leds. Using this you will need only one 3V battery if you chose a low current microcontroller ;) Think about this :) smaller size ,lower components, better artwork , low weight,no external wires needed( you put the battery on a cr2025 socket)
I hope my explanation are clearely :)

Thanks. For the pendant, I was aiming for something extremely simple, which wouldn't require any programming (and it's been ages since I've done any assembly programming) or chemicals. I considered using other LEDs but I liked the look of the "classic" red LEDs. I didn't think the smaller LEDs or the super bright ones (which look clear until lit) would provide as much visual interest when the LEDs weren't lit up.
That said, your ideas for improvements should be really helpful for those who want to take it further. A lot of people here have the equipment, knowledge, and experience to etch their own boards and program microcontrollers. With your great suggestions, there's a ton of possibilities.

I totally agree! I can't believe you think you only have "basic skills". You sure blew me out of the water! I'd be letting the world know how clever I was if I had made your beautiful pendand! 10/10

Thanks for the kind words (from both you and handprints). I think the pendant took more patience than skill. I do wish I had a bit more time to properly do the wire frame. I was in a bit of a rush to finish it so I could do the writeup for the instructable. It's actually my first attempt at doing a wire frame for jewelry so it's definitely rough. You can especially see it in the bottom corners. If I do anything like this again, I'll definitely have to take my time and improve my skills.

awesome piece of design and thought provoking gear mate. I've been playing with freeform circuitry, where you dump the board and make the wiring connections part of the design. Another thought would be to try making it solar powered so during the day it recharges and then when you put it on at night time it lights up. I've canablized solar garden lights for this kind of thing and found them cheap and readily available and most important.... cheap :)
I swap out the solar panel provided for the ones in solar powered calculators. The batteries can be replaced with super cap capacitors. Small but if the power drain is small, can keep flashing all night. Try the LEDs out of dumped mobile phones. That'll also give you a whole new learning curve on small scale soldering heh heh
Keep up the great work

Stephen