The project entailed a pneumatic cannon with valves controlled electronically. When the cannon electronics receive a certain message over Bluetooth, the appropriate barrel fires. On the other side, an Android app uses the phone's Bluetooth modem to send messages to the cannon. This approach allows the cannon to be fired from around a 30-foot range, line-of-sight.
Here is a brief video describing what we'll be making:
We started the project on a Friday night and finished the bulk of by Saturday night. We worked pretty much non-stop, and all had experience working on this kind of stuff. With that said, we'd recommend carving out a whole week if you're working on this by yourself. So now that you're enticed beyond your wildest imagination, let's get started.
Please remember to be safe while building and using this device. You are entirely responsible for what you do with this information.
Step 1: Shopping List
Arduino Uno (1x, $29.95 each)
BlueSmirf Silver Bluetooth Modem (1x, $39.95 each)
Male Break Away Headers (1x, $2.95 each)
Solid Hookup Wire (1x, $10.95 each)
150-psi Inline Sprinkler Valve (2, $11.99 each)
Bicycle Tire Inner Tube (2x, $3.99 each)
6" x 4" x 2" Project Box (1x, $5.29 each)
SPST Relay (2x, $3.19 each)
Breadboard-Style Prototyping Board (1x, $2.19 each)
2" Diameter PVC
3" Diameter PVC
1" Diameter PVC
2" PVC Endcap
2" PVC Elbow
3" to 2" Reducer Bushing
1" Schedule 40 PVC Adapter
3" to 2" PVC Adapter Coupler
2" 45 degree PVC Coupler
PVC Primer and Cement
You'll also need some tools:
Soldering iron with solder
Solder sucker (unless you're really good)
Flush cutters (optional, for a professional finish)
Heat gun and heatshrink tubing (optional, for a more durable finish)
Also, please note that you can get ranges up to 350 feet if you are willing to spend an extra $25 on a Bluetooth modem, assuming your phone's hardware also supports that range. The BlueSmirf Gold is also available from SparkFun with a very similar interface. Please note, however, that the pin order is slightly different between the silver and gold models. It shouldn't be too bad to convert from one to the other though.