Electronics All-in-One For Dummies
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The figure shows a typical animatronic prop used in a Halloween haunted house. The prop is a large jack-in-the-box that benignly plays "Pop Goes the Weasel" while a crank on one side of the prop slowly spins until an unsuspecting visitor approaches it.

Then — all in one frightening moment — the music stops, the lid flies open, a large clown head pops up, a bright light comes on to ensure that you can see the clown, and a ghastly voice screams, "Trick or treat!"

A moment later, the light goes off, and the clown retracts back into the box. A few seconds after that, the crank starts spinning and the music plays again while the jack-in-the-box waits for another victim.

The jack-in-the-box prop.

The basic pop-up operation of the jack-in-the-box is accomplished with a compressed air mechanism that can be controlled with an electrically activated valve. When the valve is closed, the mechanism is retracted inside the box. When the valve opens, compressed air flows into an air cylinder that extends the mechanism upward. The clown head is mounted on top of the mechanism. The lid of the jack-in-the-box is positioned such that the clown's head pushes the lid open when the mechanism extends. Gravity takes care of closing the lid when the mechanism retracts, and the clown goes back into the box.

Note that the point of this chapter is to show you how to build the electronic part of this prop — the prop controller that controls the prop's action. This chapter doesn't show you how to build the prop itself. The prop controller is generic enough that it can control just about any prop that includes simple actions such as pneumatic pop-ups, motors, lights, and sound. In fact I've used this very same design for half a dozen different Halloween props.

Nevertheless, it's beneficial to see how the prop controller works in a specific prop, so the following paragraphs describe in general terms how I built the jack-in-the-box prop. This will give you a general idea of how it operates so that you can see how the prop controller works with it.

  • The most important component of this prop is the pneumatic lifting mechanism, purchased for about $250 from an online distributor of Halloween prop mechanisms. If you search the web, you'll find several distributors that make safe, professional-quality compressed-air mechanisms. Just search for Halloween prop lifter and you'll find several suppliers. You can also find them for sale on eBay.

    The lift mechanism.

    The lift mechanism includes the welded steel frame, a pneumatic cylinder that provides the motion needed to lift the frame, and an electrical valve that can be connected to a compressed air hose. When the valve is connected to a source of compressed air and voltage is applied, the valve opens to allow compressed air into the cylinder.

    Do not, under any circumstances, attempt to cut corners by building your own lifter mechanism unless you are an experienced metalworker. The Internet has plans for similar devices made out of sprinkler pipe or bicycle pumps, but putting compressed air into plastic or metal parts that were not designed to handle compressed air is an excellent way to maim or even kill someone.

  • The prop is housed in a 22-inch square box constructed from 5/8-inch plywood, reinforced inside with 2x2-inch lumber. All six sides and the lid can be cut out of a single 4x8-foot sheet of plywood.
  • To create the lid, use a sabre saw to cut out the opening. Then, cut a separate piece of plywood about 1 inch larger than the opening to use as the lid. Use a pair of small gate hinges to connect the lid to the box.
  • The lift mechanism is mounted directly to the bottom of the box. Depending on the design of the mechanism you use, you may have to mount the lift on the back of the box instead of the bottom.
  • Drill two 1-inch diameter holes in the back of the box to pass the electrical power cord and the compressed air hose into the box.
  • The clown consists of a small foam wig head purchased at a thrift store and a mask purchased at a seasonal Halloween costume shop.
  • A surplus automotive windshield wiper motor turns the crank. You can find them for sale on the Internet for about $15. Fabricate the crank itself from a few pieces of scrap metal.
  • The prop controller is mounted inside the box, secured to one of the side panels with four screws.
  • To trigger the prop, an infrared motion detector called a PIR is used. The motion detector is mounted to the outside of the box and connected via a 24-inch cable to the prop controller. When the motion detector detects nearby motion, the programming in the prop controller triggers the prop to activate the valve so the clown pops up.
  • To light up the clown's face when he pops up, use a 75 W white flood lamp mounted in a plastic flood lamp holder from a home improvement store.
  • For the sound, use a set of inexpensive speakers. The speakers are connected to the audio output from the prop controller's sound board. This sound board includes a 20 W amplifier, which is more than loud enough to give a good scare when the clown pops up.
  • The figure shows a wiring diagram of the prop so you can get an idea of the prop's electrical requirements. As you can see, the prop requires a total of three 12 VDC power adapters, commonly known as wall warts. The first is to power the prop controller, the second provides 12 VDC for the windshield wiper motor, and the third provides 12 VDC for the pneumatic valve.

    To simplify the wiring, used three six-outlet power strips and an eight-terminal barrier strip, which aren't shown on this diagram. One of the power strips plugs directly into a wall outlet to supply the main 120 VAC power for the prop. The other two power strips are connected to the RC-4 relay control board. Using these power strips allows you to simply plug in the 12 VDC power adapters and the flood lamp holder.

Schematic diagram for the jack-in-the-box prop.

The prop runs on 120 VAC household power, and there are several exposed electrical connections inside the box. Therefore, it's imperative tohat the inside of the box is inaccessible to humans.

It's especially important that the wiring is secure enough to withstand the vibrations that the box will experience every time the prop is activated. When the valve closes, the cylinder extends, the lid swings open, and the clown pops up his head, the box will be jolted more than a little. To insure that the frequent shaking doesn't cause any electrical connects to come lose, all electrical wires are fastened down with wire holders, and all connections are made with soldered terminals that are tightly screwed to the barrier strip.

That's about it for the jack-in-the-box prop itself. Although the primary focus here has been in building the prop controller that provides the brains for the jack-in-the-box prop, the prop controller can be used for any other type of prop with similar requirements. And, if your prop is more complex than the jack-in-the-box, you can easily expand the prop controller by including additional relay control boards to control more devices.

About This Article

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About the book author:

Doug Lowe is the bestselling author of more than 40 For Dummies books. He's covered everything from Microsoft Office to creating web pages to technologies such as Java and ASP.NET, and has written several editions of both PowerPoint For Dummies and Networking For Dummies.

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