Experiment 14: A Pulsing Glow
122 Chapter 3
- You can put the battery in a pocket, and mount the flasher on the outside
of the pocket, with a thin wire penetrating the fabric. Note that the tiny
power connector on the perforated board will accept two 22-gauge wires
if they are solid core, or if they are stranded (like the wires from a 9-volt
battery connector) but have been thinly coated with solder. - You could mount the battery inside the crown of a baseball cap, with the
flasher on the front. - You can put together three 3-volt button batteries in a stack, held in some
kind of plastic clip. If you try this option, it may not be a good idea to try
to solder wire to a battery. You will heat the liquid stuff inside the battery,
which may not be good for it, and may not be good for you if the liquid
starts boiling and the battery bursts open. Also, solder doesn’t stick easily
to the metallic finish on most battery terminals.
Most LEDs create a sharply defined beam of light, which you may want to dif-
fuse to make it look nicer. One way to do this is to use a piece of transparent
acrylic plastic, at least 1/4 inch thick, as shown in Figure 3-82. Sandpaper the
front of the acrylic, ideally using an orbital sander that won’t make an obvious
pattern. Sanding will make the acrylic translucent rather than transparent.
Drill a hole slightly larger than the LED in the back of the acrylic. Don’t drill all
the way through the plastic. Remove all fragments and dust from the hole by
blasting some compressed air into it, or by washing it if you don’t have an air
compressor. After the cavity is completely dry, get some transparent silicone
caulking or mix some clear five-minute epoxy and put a drop in the bottom of
the hole. Then insert the LED, pushing it in so that it forces the epoxy to ooze
around it, making a tight seal. See Figure 3-82.
Figure 3-82. This cross-sectional view shows a sheet of transparent acrylic in which a hole
has been drilled part of the way from the back toward the front. Because a drill bit creates
a hole with a conical shape at the bottom, and because the LED has rounded contours,
transparent epoxy or silicone caulking can be injected into the hole before mounting the
LED.Try illuminating the LED, and sand the acrylic some more if necessary. Finally,
you can decide whether to mount the circuit on the back of the acrylic, or
whether you want to run a wire to it elsewhere.