Rainbow LED Paperweight

by talk2bruce

17K755

Intro: Rainbow LED Paperweight

Build a mesmerizing and entertaining paperweight with lights that slowly change color.  This project embeds a simple circuit consisting of nine color changing LEDs in a paperweight made of epoxy resin.  Constructing the circuit requires very basic soldering skills and the epoxy resin for making the paperweight is very easy to work with.  The result is a terrific paperweight for anyone who likes desk toys or gadgets with blinking lights and the paperweight makes a terrific gift. 

This video shows the Rainbow LED Paperweight in action. 

STEP 1: Parts List

You will need the following parts and materials for this instructable:

Paperweight Materials
  • EasyCast Clear Casting Epoxy Resin (8 oz kit)
  • Castin'Craft MC5 Mold (3" diameter x 1 3/8")
  • Black pigment for polyester, epoxy, and urethane casting
  • Castin'Craft Mold Release
  • Multi-color glitter
  • 6 Plastic mixing cups (you will use two when mixing each layer)
  • 6 wood mixing sticks or tongue depressors
  • Plastic gloves
The EasyCast Epoxy Resin, Black Pigment, Mold Release, MC5 mold, and mixing supplies are available from TAP Plastics.  Glitter can be found at most art or craft stores.

Electronics
  • Nine (9) slow color changing RGB LEDs
  • 9 volt battery
  • 9 volt battery clip
  • 270 Ohm 1/2 watt resistor
  • Solderless breadboard and wire (optional)
The LEDs are available on eBay (I got mine from the eBay seller "bestshop2008hk").  The rest of the parts are available from RadioShack or most electronics parts suppliers.

Miscellaneous
  • Small piece of scrap corrugated cardboard (4" x 4")
  • 3" Diameter round cardboard container lid or something similar (available at craft stores like Michaels)
  • Black Sharpie for coloring the cardboard container lid
  • Small rubber feet with adhesive backs (available from any hardware store)
Tools
  • Awl or equivalent pointy tool
  • Wire cutters / wire strippers
  • Soldering iron and solder
  • Scissors

STEP 2: How It Works

The Rainbow LED Paperweight consists of a simple circuit of nine slow color changing LEDs embedded in epoxy resin. There are three layers of epoxy resin: a clear top layer with a small amount of glitter mixed in, a small layer embedding the top half of the LED's, and a thick layer filling the remainder of the mold with black pigment mixed in with the epoxy.  This layer hides the LED wiring and makes for a nice background for the slow color changing LEDs.  A cross section is shown below.

The circuit is very simple as shown in the schematic below.  Nine slow color changing LEDs are wired in parallel with a 270 ohm 1/2 watt resistor between the positive side of the battery and the LEDs.  A standard 9 volt battery is used to the power the LEDs.

Because the LEDs don't change color at exactly the same time and because they are wired in parallel and draw current at different rates, the LEDs will get out of sync and you'll see different colors at the same time and some may flicker and vary in brightness.  This produces a nice rainbow effect in the paperweight.

STEP 3: Make the Paperweight's Top Layer

The first step is to make the top layer of the paperweight.
  1. Follow the directions on the Mold Release and apply it to the mold. You will need to wait for it to dry before going to step 2 below.  This is an extremely important step: if you do not properly apply the mold release you will have a very difficult time removing the paperweight from the mold and may have destroy the mold in the process of getting it out (this is experience talking here!).
  2. Follow the directions that come with the epoxy resin and mix up a total of one ounce (half ounce of the epoxy and half ounce of hardener).  This stuff is very easy to work with - just wear gloves when you're mixing it to keep it off your hands. Don't worry about bubbles: this epoxy resin is designed to "degas" and if you follow the directions, there will be no bubbles when the epoxy hardens.
  3. Add a pinch of glitter to the mixed epoxy and hardener.  Don't add too much - a small amount of glitter really works best.
  4. Pour the mixture into the mold and put it somewhere it won't be disturbed while hardening.  The epoxy takes about 24 hours to harden.

STEP 4: Test the LEDs

It's a good idea to test the LEDs before soldering them all together and embedding them into the epoxy resin.  You can test them individually or if you have a solderless breadboard, you can easily test them all at once.

If you want to test them individually, connect the longer wire on the LED (the anode) to one end of the resistor, connect the other end of the resistor to the positive side of the 9 volt battery, and connect the shorter wire on the LED (the cathode) to the negative terminal of the 9 volt battery as shown in the diagram below. The LED should illuminate and start changing colors.  If it doesn't, check your connections.  If your connections are correct, then the LED is defective and you should discard it.  Repeat for each LED.

If you want to test them all at once, plug them into a solderless breadboard with the longer wires on the LEDs (the anodes) plugged into the positive (red) strip on the breadboard and the shorter LED wires on the LED (the cathodes) into the negative (black) strip on the breadboard as shown in the photo below.  Plug one end of the resistor (doesn't matter which) into the positive (red) strip and connect the other end to the positive (+) terminal of the battery.  Plug a wire into the negative (black) strip on the breadboard and connect the other end of the wire to the negative (-) side of the battery. All the LEDs should illuminate and start changing colors. If none do, check your connections. If some don't, make sure they are properly plugged in to the breadboard.  Discard any LEDs that are defective.

STEP 5: Wire the LEDs

In this step, you will prepare the LEDs for embedding in the paperweight.
  1. You will need to create a template to hold the LEDs in place while soldering them together.  Take a piece of corrugated cardboard and draw a 2 inch diameter circle on the cardboard and draw lines to mark the center of the circle as shown in the first photo below.
  2. Using an awl or some other sharp pointy tool, make eight 5 millimeter holes evenly spaced around the circumference of the circle and one in the center as shown in the second photo.  I recommend you make a small hole first, then try to fit an LED into hole and then gradually make the hole larger until the LED fits snugly into the hole.  
  3. Bend the LED wires as shown in the third and fourth photos. You want to have the longer LED wires on the outside of the circle and you will want to have the bent leads long enough to touch the next LED in the sequence as shown in the fifth photo.
  4. Solder the LEDs to create a parallel circuit as follows:
    • Solder all the outer wires (the longer LED wires) to each other as shown in the sixth photo.
    • Solder all the inner wires (the shorter LED wires) to each other as shown in the sixth photo.  Do not allow any of these wires to touch the outer wires.
    • Solder the center LED as shown in the sixth photo - the long wire from the outer LED to the center LED's long wire and the short wire from the outer LED to the short wire on the center LED.  Be careful when soldering the center LED because it's easy to confuse the LEDs and it won't work properly if the wires are connected incorrectly.
    • Solder the resistor to the longer LED wire in the center. The resistor should be flat and parallel to cardboard.  Bend the unsoldered resistor wire to point up (perpendicular to the cardboard).
    • Bend the excess wire on the center LEDs cathode (shorter wire) to point up perpendicular to the cardboard as shown in the sixth photo.
  5. Test the LEDs by connecting the resistor the positive (+) terminal on the 9 volt battery and the other bent wire to the negative (-) terminal on the 9 volt battery.  The LEDs should illuminate and start changing colors as shown in the seventh photo.

STEP 6: Embed the LEDs in the Next Layer of the Paperweight

In this step, the LED assembly will be embedded into the next layer of the paperweight.
  1. Remove the LED assembly from the cardboard by gently pressing on each LED. Try not to bend the assembly: you will need it to sit as flat as possible as shown in the first photo.
  2. Proceed with this step only after the first layer of epoxy you poured in the earlier step is completely hardened. Make one ounce of the epoxy resin mix by combining a half ounce of the epoxy with a half ounce of the hardener according the directions that came in the package.
  3. Slowly pour the mixed epoxy into the mold.
  4. Place the LED assemble into the mold and center it in the mold as shown in the third photo. You can move the LEDs around to get it centered. Note that only the the very tops of the LEDs will be in the epoxy - the wires connecting the LEDs should not be in the epoxy.
  5. Place the mold in a place where it won't be disturbed for the 24 hours it needs to harden.

STEP 7: Pour the Final Layer

In this step, the last layer of the paperweight will be mixed and poured.
  1. Before starting the next layer, look at the LED assembly and make note of the position of which perpendicular wire is connected to the resistor. Once you pour the third layer of epoxy resin you will no longer be able to see the wiring and you'll need to know which wire is which later in this step.
  2. Mix up 3 ounces of epoxy resin (1.5 ounces of epoxy and 1.5 ounces of hardener).   You may wind up with a little more than you need but it's better to discard some than to have to mix more in a hurry.  As you mix the epoxy, use one of your clean mixing sticks or tongue depressors to add a dab of the black pigment.  The resulting mix should be pitch black: if not add some more pigment.  I recommend wearing a smock or apron and plastic gloves while working with the black pigment as this stuff stains and will never come out of your clothes and takes a long time to wear off your skin (again, experience talking here).
  3. Place the mold in a place where it will not be disturbed and slowly pour the black epoxy into the mold and fill the mold to the top, as shown in the second figure, being careful not to overfill the mold.  The two wires for powering the LEDs should be sticking out of the epoxy.
  4. After the epoxy has hardened (24 hours), remove the paperweight from the mold according the directions that come with the mold and the epoxy. You may have to use pliers to grab the lips of the mold and gently pull the mold away from the epoxy in order to pop it out of the mold.
  5. Using your notes of which wire is which, solder the red wire from the 9 volt battery clip to the positive (resistor) wire sticking out of the paperweight.  Solder the black wire from the 9 volt battery clip to the other wire.  Gently bend the wires to be flat with the surface of the paperweight as shown in the third photo.
  6. Attach four rubber feet to the bottom of the paperweight as shown in the fourth photo. The rubber feet will provide clearance for the wires and prevent it from slipping off the battery case you'll make in the next step.

STEP 8: Test the Paperweight

Before proceeding to the last step, this is a great time to test the paperweight and see the fruits of your labor.  Connect the 9 volt battery to the battery clip and you should see the LEDs illuminate and start cycling through the colors as shown below. Because the LEDs don't change color at exactly the same time and because they are wired in parallel and draw current at different rates, the LEDs will get out of sync and you'll see different colors at the same time and some may flicker and vary in brightness.  Pretty cool!

STEP 9: Build the Base and Finish the Project!

There isn't enough room in the paperweight itself to carve out space for the battery and because it takes away from the aesthetics to have wires sticking out and going to the battery, a small round cardboard lid can be used to make a battery case.  If you can find a lid the same diameter as the paperweight (3 inches), it will look very good.
  1. Draw a rectangle the size of the battery on the lid as shown in the first photo.
  2. Cut out the rectangle as shown in the second photo.
  3. Make sure the battery with the clip fits in the cutout as shown in the third photo.
  4. Using a black Sharpie or marker or paint, color the outside of the lid black as shown in the fourth photo.
  5. Connect the battery to the clip while holding the paperweight and base together as shown in the fifth photo.
  6. Flip over put on your desk and enjoy your Rainbow LED Paperweight!

STEP 10: Additional Ideas

There are a lot of interesting variations to this project.  You can use different shapes and size molds: there are square molds like the MC6 mold (3" x 3" x 1 1/16") or round cylindrical molds like the MC3 mold (2 3/8" diameter x 1 1/8").  You can also use different color pigments for the base or if you like the way the wires look you can leave the pigment out of the last layer.

The photos below show a transparent square Rainbow LED Paperweight.  This is made the same way as the one described in this instructable except that no pigment was used in the final layer of epoxy resin.

5 Comments

agis68 12 years ago

wow! really beautiful

gloriousfactory 13 years ago

we are manufacturer of leds in Guangzhou, skype: gloriousfactory

talk2bruce 13 years ago

The circuit is a parallel circuit as shown in the schematic on step 2. If your question was because of the cross section diagram on the same step, that's not intended to be a wiring guide or schematic showing three LEDs and resistors in series but to give folks a view of what the paperweight looks like when viewed from the side and how the LED assembply fits into the multiple layers of epoxy resin.

Electronics Blurred 13 years ago

Erm , excuse me sir , how do you add 3 LED's and a resistor (which is even larger then my circuit) .
into a 9V circuit ?
If it's parallel , i would believe you .
2 in a line at max . and a 150ohm resistor .
this how i wire it up .
I Positive
R Resistor 1
O LED 1
O LED 2
I Negative