Set Up Your Garage

Build a path or a maze for trick-or-treaters to follow as they dodge the lasers. An easy and inexpensive way to make walls is to use cardboard or PVC tubes attached to the floor and ceiling, and wrap caution tape between them to form walls. The caution tape also leaves plenty of space for the lasers to pass through. After you have the walls built, set up the red light and power strip/servo you prepared. Make sure you have enough wire attached to the servo to reach your Arduino.



You will need a fog machine so the lasers beams are more visible. There are several Instructables for fog chillers if you want the fog to stay low to the ground, but it isn't necessary. It also helps keep fog in the garage if you block off parts of the garage doors with cardboard walls or some other kind of barrier to keep wind out and fog in.



Set Up The Lasers

The lasers are not connected to the Arduino or PC in any way. The laser pointers come with AAA batteries by default. The batteries die quickly when you leave the laser on constantly. You can leave the battery cover off of the laser case, and power them with D-cell batteries instead. This will help extend the run time, and it will provide a more constant brightness. Use alligator clips or solder to connect wires to the spring(negative) and threaded part of the laser case(positive). Two D-cell batteries will power 2 laser pointers for over 6 hours. Each green laser pointer draws around 250-300mA, so keep that in mind if you come up with an alternative way to power them.



Once you get the lasers powered, position them in your garage. Put them 4-8 inches off the ground so that costumes with dresses or robes can make it over them. Use L brackets to fasten the lasers to the wall, or mount them on boxes or wood blocks. Use black tape to hold the power button on. The floorplan picture shows how I set up the lasers and walls in my garage. I put a caution tape or cardboard wall in front of the lasers and sensors to prevent people from accidentally bumping or kicking them.



Set up the Arduino and PC

With the lasers in place and powered on, it is easy to position your light sensors. Mount the light sensors on the opposite wall so the lasers shine directly on them. Make sure you have enough wire on your light sensors to reach your Arduino. Plug in your light sensors and servo to the breadboard according to the circuit diagram on step 3. Plug the USB cord in to your Arduino and PC, and start up the Processing program.



Remember that you can use the Arduino's built in reset button to get a new average light reading and alarm trigger values as the ambient light and fog in your garage change. The bar graph display from Processing should help you get everything tuned and working perfectly.





You should have everything up and running at this point! The next few steps provide information on how the Processing and Arduino programs work, along with pictures and videos from Halloween 2012.