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Clap Sensor

This project started as an attempt to make a clap sensor, but resulted in a sensor that is sensitive not just to loud claps, but bumps, and jiggles, and jolts. -Margaret
stuff you need
  • A large, sturdy box
  • Scrap wood (you'll need 2 larger pieces and maybe some small scraps)
  • A large nut and a long bolt
  • Plastic wrap
  • Aluminum foil
  • Double-sided tape, duct tape
  • Alligator clip sensor
  • A mat knife
  • Hot melt glue gun and glue

You can make this sensor with a bucket or a box - any large, sturdy container. Here, I'll show to make one with a box.

Cut out one side of the box. Make the opening on the box a little narrower than the width of your plastic wrap.

Tape up the seams and flaps on the box.

Attaching the plastic wrap to the box was a little tricky.

When I tried to stretch a piece of plastic across the tape, the plastic wrap just balled up, stuck to itself, and pulled the tape off the box.

It worked better to gently roll out the plastic over the tape, just pressing it lightly in a couple places to hold.

Then I could reposition the plastic, working my way around the box, pulling it slightly tighter.


Next, I added pieces of duct tape. It stuck well to the plastic and I could reposition it on the box to pull the plastic tighter and tighter, working my way around the box.

When the plastic was tight and smooth, I taped all around with more duct tape.

Next, cut a 1" wide strip of tin foil. The strip should be a few inches longer than half the height of the "drum" of your bucket or box.

Put a piece of double-stick in the center of the plastic and at th edge of the box and press the foil into place. The foil should extend just a little beyond the center of the drum and one or two inches beyond the edge of the box.

Here's how the foil looks on the box.

Now you'll attach your box "drum" to a board to hold it steady and vertical.

Find (or cut) a piece of scrap wood wide enough to hold your "drum" and about 8 inches longer.

Hot glue the box into place onto the board. Leave about 8 " between the drum and the end of the board.

Next, you'll add a vertical board that will hold a bolt that touches the tin foil when the plastic drum vibrates.

Choose (or cut) a piece of scrap wood that is about the height of your drum or a little shorter. Position it about 2 " in front of the drum surface, with one edge even with the middle of the tin foil (it will be off-center on the board). Trace around the vertical to mark its spot.

Next, mark the position of the nut that holds the bolt on the verical. This spot should be about 1/2 above the end of the tin foil, close to the center of the drum.

Glue the nut to the vertical board. It should be perpendicular to the board, so that it can hold a bolt close to the foil.

Now, glue the vertical board into place.

Here's the board in place with the box drum.

Carefully screw the bolt into the nut until the end of the bolt is close to the tin foil.
Finally! Connect an alligator clip sensor. One end clips on to the tin foil at the rim of the drum and the other clips on to the bolt. Plug the sensor into the Cricket.

Here's a sample program you can try with your sensor. It beeps when the bolt is NOT touching the foil, and when it touches the foil, it makes a two-note siren-like sound.

Here's a larger image of the program.

Now you can fine-tune the position of the bolt. You want it as close as possible to the foil, but not touching, so that the slightest vibration will make them touch. It is easiest to adjust the bolt position while the program is running - then you'll know when it is touching.
The box sensor worked great. It seemed floppy (the cardboard wasn't strong) and it was hard to pull the plastic tight, but it was fairly sensitive. It could respond to a loud clap, but would also respond if someone bumped the table.
The box sensor was remarkably sturdy. Here is in action as a "toddler sensor." (Interesting note: this boy played and played with the sensor, and the plastic got all stretched out. By the next day, however, it had tighted back up.)
What else
Learn to make copper sensors.
Read what Margaret wrote about her interactive storytelling idea.
Will food conduct electricity? Read about an activity that combines food and Crickets.

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