Test the circuit by pointing the laser pointer at the first photoresistor, PR1. The test LED should immediately shut off.
When the laser beam is interrupted or turned off the test LED should immediately light up.
If the circuit doesn't work, check the circuit against the schematic in the previous step and test the LED by placing it and the resistor in series with the battery directly.
Also make sure the LED polarity is correct. The shorter wire should be connected to the output of the IC and the longer wire should be connected to the resistor whose opposite side is connected to the positive side of the battery.
If you're struggling with the circuit, enlarge the two images included with this step and just copy it directly.
Next you need to carve two pumpkins. I chose a large pumpkin to breathe fire and a smaller pumpkin to hide the laser trigger circuit inside.
Remove the LED and resistor from the Test/Trigger output and run two pieces of wire about 2-3 feet long. Place a small piece of steel wool between the trigger wires. The wires should not be touching, but should form a short circuit through the steel wool.
When the circuit is triggered, the steel wool will burn to ignite the breath of fire.
The detector should then be hidden in the smaller pumpkin and the trigger wires and steel wool placed inside the other pumpkin. Small holes in the back of the pumpkin will make this well-hidden.
Adjust the laser to shine on PR1 and turn on the circuit. I hid the laser pointer inside a small BBQ grill across the porch....use your creativity to hide yours!
ONLY AFTER this is all set up, run a propane line with a slow flow into the back of the larger pumpkin.
We'll assume you're ok with this, but you can opt-out if you wish.