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The following information is a single lesson in a larger project. Find more great projects here.

Project Overview:

In this project, you will create a pressure-sensitive drink coaster. A foam disc is layered over a piece of foil and a pressure sensitive circuit, so when the guest places their water glass down, an LED lights up the glass.

Step 1: Introduction

In this project, you will create a foam drink coaster that lights up when you set a glass on it. To make this happen, you'll build a simple pressure-activated switch using aluminum foil. A clear glass with water is the drink of choice - the LED shines through it!

  1. The circuit in the Workplane represents the two components that are involved in the coaster circuit. While the circuit is simple, the silver ink pattern will end up taking the shape of a round coaster.
  2. Continue to the next step.

Step 2: Bill of Materials

You will need the following components and supplies to complete this project:

Circuit supplies

Circuit Scribe conductive ink pen

Circuit Stencil

Steel sheet, or another magnetic surface

9V battery and adapter

Bi-LED module

Craft materials

Colored card stock

~8 mm thick craft foam OR thin craft foam sheets with adhesive backing

Scissors and/or X-acto knife

Compass OR round object to trace

Aluminum foil

Tape

  1. Continue to the next step.

Step 3: Prepare the Circuit

In this step you will create a pressure-activated switch using a Circuit Scribe pattern and a strip of tinfoil. When you press down on the foil (i.e. put your drinking glass down) the circuit is completed and the light turns on.

We recommend using your compass to help create the outline for the coaster.

  1. Use the compass to draw a 4" diameter (2" radius) circle on the card stock. Add a 1.5 x 1.5" tab to the side, where the battery will be attached.
  2. Cut out the shape that you outlined!
  3. Next use the Circuit Stencil to add pads for the LED and battery. You can use the mark from the compass to figure out where the center of the circle is!
  4. Connect one battery pad to the closest LED pad, as shown below.
  5. Next, draw two partial circles that are about 2.75 and 2" in diameter, as shown in the picture.
  6. Connect the OUTER circle to the empty battery pad. Connect the inside INNER to the empty LED pad.
  7. The next step is to create "teeth" that interlock with each other at the top and bottom of the circle. These are the areas where the aluminum foil will press down and complete the circuit.
  8. Cut a strip of aluminum foil that fits between the LED pads. Attach it to the center of the circuit with a folded piece of tape. Note: do not let the aluminum foil touch the two LED pads -- it will short the circuit!
  9. Now you can test the circuit! Put the circuit on the steel sheet or another magnetic surface and add the battery and LED modules.
  10. Press down on the aluminum foil to complete the circuit!
  11. Continue to the next step.

Step 4: Make the Foam Coaster

In this step you will cut out the foam coaster that conceals the circuit.

You can either use a 8 mm thick craft foam piece, or several sheets of thin craft foam glued together. We're using 2 mm thick adhesive backed foam in this example.

  1. Use the compass to outline a 3.5" diameter (1.75" radius) circle on your craft foam.
  2. Cut the circle out using scissors or your X-acto knife.
  3. In the center of the circle, trace around the bi-LED component. You can use the mark left by the compass to find the center.
  4. Cut out the hole for the bi-LED module.
  5. If you used the 8 mm craft foam, you are finished! If not, you can repeat this process and stack multiple craft foam cutouts and stick them together using glue or their own adhesive backing.
  6. Finally, assemble the circuit again with the foam coaster nested over the bi-LED. The coaster should fit loosely around the LED module and the light should be off. If it feels tight, you can trim out some extra foam using the X-acto knife.
  7. Continue to the next step.

Step 5: Use It!

Assemble your coaster circuit on top of a magnetic surface. For a fancy table setting, you can place the Steel Sheet (or whiteboard, etc..) under a table cloth. In our pictures below, we hid our Steel Sheet under a piece of white poster board.

Get a glass of water ready to test the coaster!

  1. Try pressing down on the coaster with your fingers. Does the light come on?
  2. Next, try it with a glass of water. The effect is especially neat if you dim the lights in the room!
  3. Congratulations on completing the light-up coaster using a pressure sensitive with a minimal number of parts. Try filling the glass with different drinks or materials to see how the light diffusion changes!

Congratulations, you have completed this project!

Check out other great projects here.

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