We've all seen them, they're welcome mats for outside your front door that make spooky sounds whenever a trick or treater comes knocking. I'm going to show you how to make half of this, so that you can use it for lights, sounds, or some kind of motor powered device (like a skeleton that waves when you step on the plate). Pressure plates work very simply, there are two hard pieces (the plates) with conductive material on each one (aluminum foil) and some kind of spring in between them (sponge). Wires are attached to each piece of conductive material, so when the two plates touch each other (someone steps on it) a circuit can be completed.

Step 1: Gather Materials

You'll need:

Two small rectangles of thin plywood (cardboard could work, too)
An old sponge
Aluminum foil
Wire
Some kind of adhesive
Electrical tape
Cutting implements
Newspaper to work on (easy clean up)
Something to test the circuit with (Like a motor/battery)

Step 2: Assemble Each Plate

*Glue the aluminum foil onto each plate, with a small balled up piece in the middle of each. (The plates can't get close enough together to actually touch)

Cut and glue two small squares of sponge on one of them.
Tape a wire onto each plate.

Step 3: Attach the Two Plates/Testing

Now, simply glue the plates together, via the sponges. (Aluminum foil on the inside) You're ready to test it out!

Testing:

Attach one pole of the battery directly to what you're testing on, for the other pole, attach one wire of the pressure plate to the battery, and the other to what you're testing on. Push down on the plate and hope it works!

If it doesn't

Check your connections, do both wires actually touch the contacts of the battery? Do both wires actually touch the contacts on your test subject? Are both wires touching the aluminum foil? Do the foil balls touch each other when the plates are compressed?

If it doesn't stop working

Check and make sure that the aluminum foil balls are constantly touching each other, that's most likely. If that doesn't work, add just a little bit of water onto the sponge, squeeze the sponges to work it in...that should make it a little bit springier.

Have fun!

(I had a video, but you can't tell when the motor is spinning...I'll try and get a better demonstration soon)