If the thought of dozens of tricker-or-treaters in gross-out costumes knocking down your door makes you want to spew, have we got the pumpkin for you! Every time the Arduino-Controlled Chemical Foam Spewing Pumpkin encounters a trick-or-treater at your doorstep, it spews burning chemical foam all over your front lawn. Now you can convey how much trick-or-treaters make you want to vomit, without doing any real vomiting yourself. So grab some antacid to settle your stomach, and dive deep into these helpful instructions to build your own.

Step 1: Materials

You will need:

(x1) Large round pumpkin
(x1) Square Nalgene 1000 ml bottle
(x2) Square Nalgene 250 ml bottles
(x1) 5' of 3/8" rubber tubing
(x1) 100g potassium iodide mixed in a 2M solution
(x2) 500 ml 35% hydrogen peroxide solution
(x1) dish soap (economy style, not natural stuff)
(x1) food coloring
(x2) 5/8" rubber grommets
(x2) brass check valves for liquid
(x2) 3/8" barbs
(5') rubber 3/8" hose
(x1) Teflon tape
(x4) small diameter hose clamps
(x2) self-priming pumps
(x1) PCB
(x2) 5V SPST relays
(x1) 10K resistor
(x1) Arduino
(x1) M-type connector
(x1) 9V battery clip
(x1) 9V battery
(x1) 22AWG red and black solid-core wire
(x1) 9V / 2.5A wall wart
(x1) 3' floor switch material
(x1) Halloween Door Mat
(x1) Assorted alligator clips
(x1) Assorted zip ties

How to make Chemical Foam

The chemical foam is made from mixing a few simple ingredients:
  • Hydrogen Peroxide (the stuff you put on scrapes and cuts is 3%, the one we're using is 35%)
  • Potassium Iodide (mixed in a 2M solution)
  • Dish Soap (not the eco-friendly kind - get regular stuff like Palmolive)
  • Food Coloring
When you mix the ingredients above in the correct proportions, you get foam, potentially lots of it.  Be safe when working with these chemicals and use common sense.  35% Hydrogen Peroxide is a powerful oxidizer and should be handled with rubber gloves, goggles, and long sleeves.  Always use best chemical practices when making chemical foam.
Congratulations on winning the Autodesk Halloween Contest with this entry!!!
How much or what do you mean by a saying a 2M solution?
2M refers to a molar concentration in chemistry.<br /><br />http://en.wikipedia.org/wiki/Molar_concentration<br /><br />It allows someone to mix a concentration of a solution and make any amount they like.
Tasteful and understated!
LOL!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Ya think? ;-D
And safe! I don't always spray my steps with slippery liquid, but when I do I try to do it when many children will be walking up and down them. <br> <br>Okay, sorry, was just taking the sarcastic bait. I think it's a funny project and laughed out loud. Just maybe should be pointed away from where people will actually be walking.
Nothing like spraying some kids with hot, slippery, oxidizing chemical foam. <br> <br>I like the project though. Why not just use a baking soda/soap/water solution and vinegar/water/food coloring? <br> <br>I have a couple other suggestions, but maybe I'll write a follow up instructible for them...
That came off a little too judgmental. The foam is fairly mild, but what if on of the ingredients runs out first? The reaction doesn't finish and then you're spraying foam and potassium iodide, or much worse, foam and 35% peroxide.
This is amazing! I would love to have this at my house, looks like a project for next Halloween!
Oh my heavens! This is very creative!

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