Making Pressure Pads

Robotic Art Studio:	Spring 1999
Group:	Intelligent Space
	Frederick Zeleny Ethan Frantz Mauro Fiore Christopher Linder
Date:	May 3, 1999
Author:	Fred Zeleny

Main Materials Required

1) Top and bottom board (any relatively light, slightly sturdy substance; particle board, and masonite, depending on size of pad). Cardboard works best in most situations). The silvery insulation is most likely the best choice for the bottom pad because it is 1) light, 2) cheap, 3) already is covered with conductive material. Note that we have not tested this but if we were to do this again it would be the first thing we would try. The top material should be moderatly flexible. It should not spread out weight that effectivly because then the pads will not go off.

2) Aluminum foil (standard grocery store al. foil wrap is fine)

3) Rubber/Plastic mesh (non-conductive and springy is important; anti-slip rug padding works very well)

4) Rubber bands (small thickness and length)

5) Duct Tape (you always need Duct Tape)

6) Wires (for electrical connection purposes)

Assembly

Cut out two boards in desired pad shape, one for the top and one for the bottom.

Attach aluminum foil to the top of the the bottom board (can be done with duct tape or glued, for more complete attachment); be sure to leave about an inch of non-conductive surface around edges if the pads will be next to each other. Attach aluminum foil to underside of the top board with duct tape, adding rubber bands between board and aluminum to increase sensitivity of pads (the more rubber bands you have spread out, the more increased pressure spots there will be on the aluminum; thus greater sensitivity to weight). Whenever attaching foil, be sure that it is not overly creased or crumpled; too many ridges may throw off sensitivity (which is ideally controlled by amount of rubber bands). In all of these cases, the shiny side of the aluminum foil should be pointing inwards (top of bottom pad, bottom of upper pad); it seems to be slightly more conductive.

Attach wires to corners of pads. The bottom should be the ground, the top should be the switch.

Place the mesh between the pads.

Position the top board (aluminum facing down) on top of the mesh on the bottom pad (which should have the aluminum facing up).

Be sure to test repeatedly and modify sensitivity to your needs.

Notes

Almost all of these materials can be purchased at a grocery store or at Home Depot. Be sure that the material you select is appropriate for the situation: cardboard worked well for small, testing pads, but would not be good for large, oddly-shaped pads.

Keep your pads from getting wet, and make sure that you can get to the inside of them easily. The more your pads are used, the more likely they will be to get "stuck" at on or off. To fix this, open them and examine the underside of the top board. Chances are, the aluminum foil over the rubber bands has worn off. To fix this, put another layer of aluminum foil flat ever the worn spot and secure it (with duct tape around the edges of the foil). If this does not work, try sweeping under the mesh, to see if any conductive materials have collected and are causing uncontrolled connections (can cause this a great deal).

Be sure you can easily test whether or not each pad is connected individually. Having an LED that lights when the pad is activated works well for this. This makes checking pad connections much easier.

Circuit Diagram

R1 = 10k - 15k

R2 = 220 - 512