Flare-Up Pumpkin

How to make a pumpkin that flares up with a strobe light goes off when people walk by.

This year for Halloween I wanted something flashier, so I decided to create a pumpkin that would react to people walking near it. After a bit of brainstorming I came up with this, The Flare-Up Pumpkin.

Step 1: Materials and Tools

Here follows a list of what you will need to create the pumpkin.

Materials:
- 1 Pumpkin
- 1 Tea Light
- 1 Arduino
- 1 Strobe Light
- 2 5V Relays & Sockets
- 1 Solenoid
- 1 BBQ Lighter
- 2 Photosensors (Non-IR)
- 2 Resistors to Match the Photosensors(Same Value in Used Light Level)
- Male Headers
- Heat Shrink Tubing
- Wire
- Solder
- Hot Glue
- 24V adapter (for the solenoid, it may be different for yours)
- 9V adapter (for the Arduino)

Tools:
- Soldering Iron
- Hot Glue Gun
- Wire Cutter/Stripper
- Steak Knife
- Hobby Knife (X-acto Knife)
- Drill Bits

Step 2: Program the Microcontroller

To load the attached code onto the Arduino, open the file "Flare_Up_Pumpkin.pde" in the Arduino environment and follow the standard procedure to load it onto the Arduino (it varies from version to version of the hardware).

If you are doing this I am assuming you already know how to program an arduino. If not there are some good tutorials here.

Step 3: Solder the Sensors

The light sensors work by comparing their resistance (dependent one the amount of light hitting the sensor) to a set value resistor. As the resistance of the sensor changes, the the voltage at the point between the light sensor and resistor changes. This voltage can be read by the arduino.

For this project, solder the light sensor on the end of a wire long enough to reach where it is needed. It is also good to use some heat shrink tubing around the bare wires at the end, because of the moisture in the pumpkin.

Next, expose a portion of the wire that connects to the negative sensor lead (the one to be read by the arduino). Solder one side of the resistor to the wire near the cut. The other side of the resistor needs to be soldered to the ground.

See the schematic below in the pictures for clarification and for the pins on the arduino to connect.

Solder all of the connections to go to the arduino (+5V, ground and 2 sensors) to the header, so it can be easily removed later.

Step 4: Build the Gas Supply

To construct the gas supply, start by disassembling the BBQ lighter and removing the gas container and lines.

Once that is finished, use hot glue and attach the solenoid to the gas. Attach it so that when the solenoid is activated, the gas opens. You may need to modify the solenoid so that it fits the gas supply, and so it has enough strength to turn on the gas. I modified mine (from a broken record player) by removing the spring, and flattening the spring anchors. I also added some neodymium magnets to help the strength of the solenoid.

Once that works reliably, connect the relay so that when it switches on, it completes the loop between the 24V adapter and the solenoid. See the electrical diagram in the pictures to help clarify things.

Step 5: Hack the Strobe Light

This is one of the more dangerous steps (assuming you haven't caught your eyebrows on fire yet) because of the high voltages in the strobe light.

The idea is that you want to control the strobe light by using the relay to either ground or pull up the point that controls the speed of the strobe light. So when the relay is tripped, the point gets pulled high, causing the light to flash.

I set mine up to work by first having the strobe knob set to max. I then soldered the relay so that it connects the middle of the knob(where the voltage controls the flashing speed) to the ground. This causes it not to flash. When the relay is tripped the connection is broken, allowing it to flash. (see the pictures for more notes)

Before you go using this configuration, know that it is dangerous to short the positive to the ground. My strobe has a resistor (to control the max flashing rate) between the positive and the control potentiometer(knob). This makes it so it doesn't short. If yours doesn't have one, it might be good to add it before trying this.

It is also important to make sure the relay can handle the voltages you will be applying across it. My voltmeter registered 140V DC max across the point I will be using, which is within the 150V DC my relay is rated for.

Step 6: Carve the Pumpkin

I leave this step up to you. There are many good instructables on how to carve a pumpkin and with a quick Google search you can find many free patterns.

To carve the victim I like to use a steak knife for the larger parts and a hobby knife and drill bit (not in a drill) for the finer details.

Step 7: Final Assembly

Start by drilling a hole large enough for the gas line and light sensor to detect the flame to fit through.

Next, attach all of the components to the pumpkin. I Find that the most effective way to attach the parts is using bent paper clips. However, if you are going to attach the strobe light or other heavier object to the pumpkin, I suggest using wood screws.

Once you have the sensor and gas threaded through the hole, use a couple more paper clips to anchor them to the pumpkin and aim them where they are needed. I suggest placing the gas opening 4 cm (about 2") away from the flame. Place the light sensor just off to the side behind the gas opening.

A potential pitfall is the gas may miss the flame if it is bumped or the flame height lowers, so aim accordingly. If the strobe light goes off for more then a second, this means the flame sensor missed when the gas went off, which stops the program. To fix it, just reset the arduino and adjust the sensor so it won't happen again. The continuous flash could also mean the pumpkin is low on gas, or isn't putting out enough gas, so fill it up or open the regulator if needed.

When everything is adjusted properly the system works quite reliably, producing a nice effect when people walk up.