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Finger Triggers

This info could be useful in other projects, so I put it in its own build page.

Materials:

  • Radio Shack 273-073 Piezo Element
  • Mouse Pad
  • Rigid plastic board (e.g., polyethylene -- I used some scraps, left over from my Proton Pack build, that originally were "For Sale" signs from Office Depot)
  • small (about 1/4" diameter) foam rubber stick-on feet
  • Silicon adhesive/sealer

Tools:

  • utility knife
  • cutting board
  • tin snips
  • metal straightedge

Step 1: Cut Mouse Pad

Measure the size of the pads to your liking.  I used the width of my ruler as a guide and made my pads square.  Mark the lines in pencil on the mouse pad.

With the mouse pad on a hard cutting board, use the metal straightedge as a guide and cut the pad with a utility knife.  Try to cut through the pad entirely in a single stroke.


Step 2: Cut the Plastic Squares

Cut plastic squares roughly the same size as the pads you cut in Step 1.  They don't have to be exact -- in fact, a little smaller is preferred.  I trimmed mine down using tin snips.  Another useful technique here is to score the plastic along a straight line using a utility knife, then breaking the square off by bending along the score line.

Step 3: Crack Open the Piezo Element

The piezo element comes housed in a protective plastic case:

We need to set it free from its cold, plastic home.  My preferred way to do this is to put it in a vise and squeeze the jaws until the lid pops off:


Be VERY CAREFUL!  Wear safety goggles -- the lids sometimes fly across the room.  One of these popped straight into my eye; fortunately I *was* wearing safety goggles.

Once you have the case open, gently remove the round piezo element within:

Be careful not to break the wires away from the element.

Step 4: Trim the Piezo Element to Size

Using tin snips, cut away most of the piezo element until just a small amount remains surrounding the soldered-on wires:

The smaller footprint of the modified element means less chance of your finger tapping the element directly.  They seem to work better if they pick up vibration from a little distance away.

I assume they aren't as "hot" (don't generate as much voltage when tapped), which means less chance of picking up crosstalk from other nearby triggers.

Step 5: Assemble the "Sandwich"

Using silicon adhesive assemble the trigger in the following order (top to bottom):
  1. Foam pad
  2. Piezo Element
  3. Plastic Square
  4. Foam stick-on feet (3)
For the piezo element, try to keep it on a corner, away from the middle of the pad:


For the stick-on feet, try to keep them away from the piezo element.  This minimizes vibration from other triggers reaching the element.

And that's it!




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