Make Electronics Learning Through Discovery 2nd Edition by Unknown

Author:Unknown
Language: eng
Format: epub

Experiment 18: Intrusion Alarm (Almost) Completed

To make everything look professional, you should not

just start drilling holes arbitrarily for your switches and

LEDs. You should draw a layout on paper (or use a draw-

ing program, and then print the image on paper). Just

make sure there’s room for the components to fit to-

gether, and try to place them similarly to the schematic,

to minimize the risk of confusion.

Tape your sketch to the inside of the top panel, as shown

in Figure 4-55, and then use a sharp, pointed tool (such as an awl or a needle) to press through and mark the

plastic at the center of each hole. The indentations will

help to center your bit when you drill the holes.

Figure 4-56 The exterior of the panel after drilling. A small handheld cordless drill can create a neat result if the holes were marked carefully.

I placed all the switches and LEDs on the top panel. The

power input jack is positioned at one end of the box.

Naturally, each hole has to be sized to fit its component,

and if you have calipers, they’ll be very useful for taking

measurements and selecting the right drill bit. Other-

wise, make your best guess, too small being better than

too large. A deburring tool is ideal for slightly enlarging a hole so that a component fits snugly. This may be necessary if you drill 3/16-inch holes for your 5-inch mm LEDs.

Fractionally enlarge each hole, and the LEDs should

push in very snugly.

If your loudspeaker lacks mounting holes, you’ll have to

Figure 4-55 A printed layout for the switches, LEDs, and other glue it in place. I used five-minute epoxy to do this. Be

components has been taped to the underside of the lid of the careful not to use too much. You don’t want any of the

project box. An awl is pressed through the paper to mark the glue to touch the speaker cone.

center of each hole to be drilled in the lid.

Drilling large holes in the thin, soft plastic of a project

If you’re using an audio circuit driving a loudspeaker (in-

box can be a problem. The drill bit tends to dig in and

stead of a ready-made siren) you’ll need to make multi-

create a mess. You can approach this problem in one of

ple holes to vent the sound from the loudspeaker, which

three ways:

will be beneath the top panel of the box. The panel that

I made is shown in Figure 4-56.

• Use a Forstner drill bit if you have one. It creates

a very clean hole. A hole saw can also be used.

• Drill a series of holes of increasing size.

• Drill a smaller hole than you need, and enlarge

it with a deburring tool.

Regardless of which approach you use, you’ll need to

clamp or hold the top panel of the project box with its

outside surface face-down on a piece of scrap wood.

Then drill from the inside, so that your bit will pass

through the plastic and into the wood.

174

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