Tired of coasters that just kind of sit there, not doing anything interesting? This coaster design no only protects your wooden table from the ravages of water damage, but lights up when a cup is placed on top.

Step 1: Parts Needed

White Plastic approximately 3/16" in thickness
(4) CR 2032 Batteries [Amazon]
White LED Strip Lights [Amazon] (or whatever color you prefer!)
Electrical Wire

Any plastic should do - I used part of an old light table!

*Links to Amazon are affiliate.

Step 2: CNC Cut Plastic

Cut the plastic out based on the DXF seen here. The idea is that the holes encase the CR2032 batteries, and the thin material cut down to 1/8 inch on the top section acts as a spring, connecting the wires to each battery when pressure is applied. The channels are for running the wires through the assembly.

coaster-top-bottom.dxf
Download View in 3D

Step 3: Batteries and Electrical Connections

Connect the batteries in series per the diagram, giving you 12V DC out. Hot glue as needed. Note that the wire is meant to go over the plastic then into the small holes outside the channels to make a solid connection.

This circuit took me longer than I would prefer, as it snakes around through the assembly in a strange way.

Step 4: Test and Hot Glue

Put the two halves of your coaster together, and it should light up. Apply hot glue to the corners of the bottom piece, then assemble with weight on the top piece. The idea is that when it cools it will expand slightly, breaking the electrical connection until a full glass is on top.

You may need to experiment with how thin to make the cutout top plastic dividing the inner battery section with the outer supports in order to obtain the correct spring rate for the application.

Step 5: Enjoy!

Place your drink on the coaster, and it lights up. It may need to be full in order to connect the circuit, so this is also a great way to tell others that it's time for a refill!