The Arduino Inventor's Guide (13 page)

First, cut out the templates, shown in
Figure 2-15
. In our template, the housing body is a single piece of cardboard that is meant to be cut out, scored, and folded.

Trace the template onto your cardboard, and make careful note of the dashed lines, perhaps by drawing them on your cardboard in a different color. You’ll score the cardboard along those lines to bend it, so whatever you do, don’t cut along them yet.

FIGURE 2-15:
Enclosure template for the Stoplight (not full size)

Once you have everything traced, cut out the stoplight pieces along the solid lines using a craft knife and a metal ruler, as shown in
Figure 2-16
. If you’ve never used a craft knife before, be sure to read “
Using Craft Knives Safely
” on page
56
. Score the cardboard for the housing along each dotted line, on the exterior side of the cardboard. When scoring cardboard, you take a couple of shallow passes with the craft knife (don’t cut all the way through). Don’t score the shades yet.

FIGURE 2-16:
Scoring along the template with a craft knife and metal ruler

USING CRAFT KNIVES SAFELY

You’ll use craft knives a lot in this book, so it’s important to know how to safely use them. Just like any tool, when used incorrectly, craft knives like the one here can cause injury.

Here are a few tips for using craft knives safely:

• Always pull the blade when slicing through sheet materials. Pushing or forcing the blade in any other direction raises the potential for slipping or breaking the blade.

• Be patient. Don’t try to cut through the entire thickness of the material in a single pass. Make multiple passes with medium pressure. This will save your blade and also produce a cleaner finished product in the end.

• Use a straightedge made of metal, such as a metal ruler. If you use a wooden or plastic ruler as a straightedge, you run a higher chance of your blade catching the straightedge, rebounding off the material, and ultimately moving toward your hand.

• Keep your fingers out of the way. This may seem obvious, but accidents happen.

• If your knife starts to roll off your desk, let it fall, and just pick it up off the floor. If you reach for it and catch it before it falls, you run the risk of stabbing yourself in the hand. Ouch!

• Finally, use sharp, new, and intact blades. If a blade breaks, replace it. If a blade is dull, replace it. Cutting through paper and cardboard dulls blades very quickly. Keep a supply of extra blades around, and if it’s starting to get hard to cut, replace the blade.

Once you have cut out your cardboard enclosure, add the mounting holes for the three LEDs; these should be at the little solid-lined circles inside the big dashed circles. One easy option is to carefully press a sharp pencil through the cardboard to make the holes. For cleaner holes, however, we suggest using a 3/16-inch drill bit and power drill to make holes in the cardboard, as in
Figure 2-17
. The LEDs are about 5 mm (about 0.197 inches) in diameter. You want the hole to be a nice, tight fit. So, a 3/16-inch hole (0.1875 inches) is perfect for making the fit snug for the LED.

Be careful when completing this step, and make sure to watch where your fingers and hands are relative to the drill bit. You don’t want to drill into yourself! You can also use the drill bit without the drill and manually spin it through the cardboard if you don’t have a drill or aren’t comfortable using one.

FIGURE 2-17:
Drilling holes for the LEDs

Once you have the holes drilled, remove the three LEDs from your breadboard and insert them through the back side of the cardboard, as shown in
Figure 2-18
. Remember that standard traffic lights are usually ordered red, yellow, and green from the top to the bottom. Pay attention to where the LEDs connect on the board, because we’re going to reconnect them at the end.

FIGURE 2-18:
All three LEDs pressed into the cardboard

Next, bend the cardboard along the scored lines, as shown in
Figure 2-19
. Bend the vertical sides
➊
toward the interior, and then do the same with the top and bottom sides
➋
and the tabs
➌
. (The sides and tabs are labeled in
Figure 2-15
.)

FIGURE 2-19:
Prefolding the scored cardboard to form an enclosure for the Stoplight

Position the tabs
➌
inside the vertical sides
➊
, and glue them in place as shown in
Figure 2-20
. You can use hot glue, tape, or craft glue—we prefer hot glue because it’s easy to work with, sets quickly, and has a pretty strong bond.

Repeat this for the top and bottom corners. You should end up with a shallow rectangular box with an open back.

FIGURE 2-20:
Folding and gluing the cardboard housing

The Stoplight’s lenses are made from ping-pong balls cut in half, but you can use anything that’s moderately translucent.

If you’re using ping-pong balls or something similar, carefully cut two balls in half. When doing this, place the ball against a cutting mat or thick piece of cardboard and hold it firmly at the sides with your fingertips. Carefully push the knife blade down toward the mat and into the ping-pong ball (making sure the blade isn’t pointing at you or your hand) to make an incision as shown in
Figure 2-21
. Rotate the ping-pong ball and repeat until you’ve cut all the way through. Make sure to keep your fingers away from the blade, and always cut on a cutting mat or a piece of cardboard.

FIGURE 2-21:
Safely cutting a ping-pong ball

Once you have three ping-pong ball halves (you’ll have four; one’s an extra to use in future projects or as a small hat for your favorite stuffed animal), secure them with a dab of hot glue as shown in
Figure 2-22
.

FIGURE 2-22:
The enclosure with ping-pong balls as lenses