As Halloween approaches, every electronics hobbyist wonders: Can I replace a pumpkin candle with LEDs? Yes you can!
This article will show you how to make several simple LED circuits powered by an ordinary 9V battery. No soldering is required. These circuits are also applicable and useful for robots and other electronic projects.
(If you aren’t interested in the technical stuff, you can skip ahead a couple of pages to get to the pretty pictures and movies.)
Let’s start by determining the benefits and issues of sticking with an ordinary candle. As a jack-o-lantern light source, the benefits of a candle/tea-light are:
The disadvantages of a standard wax candle are:
LEDs (light emitting diodes) have none of the disadvantages of candles. And, a well-designed LED circuit can include some of the advantages of candles. (However, if your LED circuit is somehow generating a festive pumpkin scent -- you’ve got it wired wrong.)
To me, the advantages of being able to choose different colors and the reduction of the risks of burns cause me to select LEDs over candles for lighting my pumpkins this Halloween.
This article was written in September, before any decent natural pumpkins were available on the market. Furthermore, I’d like to be able to expand this article in future years and so I need a reusable pumpkin as a standard model. As such, I decided to use an artificial pumpkin for test purposes.
An artificial pumpkin??? Horrors!
Before you get too upset, recognize that this article is about producing an artificial light source. What better place to put an artificial light source than in an artificial pumpkin? And, this project ultimately will go into a real pumpkin.
My family visited two local craft stores, Michaels Arts & Crafts and Hobby Lobby Crafts. At Hobby Lobby we selected Funkins carvable pumpkins #009 for Halloween 2007.
Unfortunately, the pumpkin has an orange interior. That’s not going to provide a strong reflection and the orange color is going to tint the lighting of any color LEDs. The inside of the fake pumpkin needs to be spray-painted white.
Left: Checking for holes in an artificial pumpkin. Right: Taping holes and underside opening with blue masking tape.
Before painting, place a bright flashlight in the uncarved pumpkin and check the outside for any holes where paint might leak out. Cover those holes with blue painters masking tape (low adhesive -- such as Scotch blue masking tape or 3M blue masking tape). If you use ordinary white masking tape it may peel away some of the pumpkin skin when you try to remove the tape.
The underside of the Funkin is already cut open. So, we'll be spray painting from that direction. Coat the outside border of the underside opening with blue masking tape to protect it from overspray.
Left: Covering pumpkin with newspaper. Right: Close-up photo showing masking tape not sticking.
Cover the outside of the pumpkin with newspaper and stick it into a paper bag. Cut a hole in the bottom of the paper and tape it as best you can.
Because the interior of the artificial pumpkin is made from polyurethane foam, the cut portions are porous and tape won’t adhere to it. Some spray paint is going to leak back there. That’s why we covered the outside bottom of the pumpkin a few steps ago.
Left: Use rubber gloves when spray painting. Right: Inside of the finished decorative pumpkin painted white.
I selected RustOleum spray paint (Plastic Primer) in white. Wearing plastic gloves, insert the tip of the spray paint can nozzle and apply a light coat of paint to the interior walls of the pumpkin.
Use short bursts as far away as you can be from the side you are painting. The ensuing paint cloud will partially coat the places you can’t otherwise reach.
Don’t try to get it all painted in the first pass. Instead, you'll have better results by letting it dry for a few minutes and then applying additional coats of paint.
After about an hour of drying, I applied a couple of light top coats in the interior using Krylon spray paint in flat white. I selected flat-white paint as opposed to satin paint or gloss paint, because I didn’t want any glare or hot spots.
My wife carved the pumpkin using serrated pumpkin carving tools. She wanted to make a highly creative or ultra spooky pumpkin, but this article requires a “model” or “idealized” pumpkin for testing purposes. Sorry dear.
Let’s see how to light up the jack-o-lantern...