Voodoo Bunny – Final Project

For my final project I was inspired by voodoo dolls to make a giant inflatable bunny that could be inflated and deflated by pressing on a smaller “voodoo” bunny. Pressing on the small bunny shuts off the bigger bunny’s fan, transmitting your push to the bigger bunny.

The plans for both bunnies were generated using a computer program that I wrote which unfolds any 3D model into a pattern that can be folded together and inflated to form the original shape. The patterns were projected onto and cut out of polyethylene sheeting, then welded together to form the bunny. More information about this aspect of the project is available here. You can see and print out the patterns I used to create the bunny at the link below:

The Voodoo Device

The voodoo trigger device is a development on my previous huggable input sensor project. When the inflated bag is pushed or hugged air flows back through the fans, slowing them down. An attached Arduino board reads this change in speed and turns off the big bunny’s fan if a change is detected.

While I had hoped to have a small voodoo bunny be the trigger device for the larger bunny, I ran into some difficulty in assembling the smaller bunny. I thought that a 3’ tall bunny would have enough internal volume to trigger the sensor, but it did not.

This was by far the most time-consuming (and frustrating) step of the project. Because it took over ten hours just to construct the 3’ tall bunny, I was not able to create a larger bunny in time for the deadline. Instead, I used the simple plastic bag membrane I was using to test the device in its place.

For posterity, I constructed the 3’ tall bunny using several computer printouts of the patterns I used for the big bunny and the same 4mil polyethylene sheeting I used or the big bunny. I welded the edges of the bunny using a soldering iron and a ruler rather than an impulse sealer. This technique yielded mixed results, and I would recommend using the impulse sealer method described in my other post.

The Relay

To control the fan using my voodoo sensor I wired a relay into an extension cord attached to the fan.

Before I describe the method I used to accomplish this…

WARNING: Switching wall electricity can electrocute and kill you! There are safer ways to wire a relay than the way I did it. If you like living, check out this great sparkfun tutorial that shows you how to switch power using a GFCI. If you’re feeling brave or lucky, keep reading.

All of the things required to build this switch can be purchased at Radio Shack:

Y-Splitter Power Cord I spliced my relay into this Y-shaped power adapter. You can use an extension cord if you want.
Electrical Tape
Heat Shrink Tubing
Relay I used a relay that I salvaged from some old electronics I found. This relay or any other single pole single throw relay under 5V will do.
Perfboard Though not necessary, this is a nice way to mount your relay for soldering.

I cut in the middle of the power cord, leaving room on each side for splicing:

Then I stripped the outside covering of the wire. Be careful not to cut the smaller wires inside. If you have slack, cut further down the wire than I am here.

I stripped the other (socket) side of the wire as well.

After stripping, three wires are visible.

Green is ground. It will be directly connected to the other piece
White is hot. It will also be directly connected to the other piece.
Black is neutral. It will be switched by the relay.

NOTE: Be sure to use only the black, neutral wire with your relay. Switching the hot wire can get you electrocuted.

I stripped each of the wires, twisted them, and soldered the green and white ones to their matching wires on the socket side. Then I insulated the solder points using heat shrink tubing.

The black wire remains free.

Then I mounted the relay to the perfboard and began wiring its connections according to this diagram. I ran long wires from the relay to my Arduino so that it was isolated from the relay.

circuit diagram

There are many different pin configurations for relays, so yours might not look exactly the same as mine.

I didn’t do a very good job of soldering this to the perfboard. You can do better!

After you’re done, wrap the whole thing in electrical tape. When wrapping, make sure that none of the wires going into the relay can touch.

The Program

Like the huggable input device, Voodoo Bunny uses the excellent Arduino FreqCounter library. The program measures the frequency of the voodoo fan’s tachometric sensor with FreqCounter to determine if the little bunny has been pushed. Once it’s determined that a push has occurred, the Arduino powers the relay, shutting off the big bunny’s fan. It then waits a set number of cycles before deactivating the relay and turning the fan back on.

The source code is available on Github at the link below:

Arduino Source

Bunny Construction

After the relay, Arduino, and sensor were set up, I turned on the power. This is what the back of the bunny looks like when it’s inflated.


~ by Max Hawkins on May 14, 2010.

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