Experiment 15: Intrusion Alarm Revisited
138 Chapter 3
tools
Four most common perfboarding errors
- Too much solder
Before you know it, solder creeps across the board,
touches the next copper trace, and sticks to it, as de-
picted in Figure 3-101. When this happens, you have to
wait for it to cool, and then cut it with a utility knife. You
can also try to remove it with a rubber bulb and solder
wick, but some of it will tend to remain.
Even a microscopic trace of solder is enough to create
a short circuit. Check the wiring under a magnifying
glass while turning the perfboard so that the light
strikes it from different angles (or use your solder wick
to suck it away).
Figure 3-101. If too much solder is used, it makes a mess and
can create an unwanted connection with another conductor.- Not enough solder
If the joint is thin, the wire can break free from the
solder as it cools. Even a microscopic crack is sufficient
to stop the circuit from working. In extreme cases, the
solder sticks to the wire, and sticks to the copper trace
around the wire, yet doesn’t make a solid bridge con-
necting the two, leaving the wire encircled by solder
yet untouched by it, as shown in Figure 3-102. You
may find this undetectable unless you observe it with
magnification.
You can add more solder to any joint that may have
insufficient solder, but be sure to reheat the joint
thoroughly.
Figure 3-102. Too little solder (or insufficient heat) can allow
a soldered wire to remain separate from the soldered copper
on the perforated board. Even a hair-thin gap is sufficient to
prevent an electrical connection.- Components incorrectly placed
It’s very easy to put a component one hole away from
the position where it should be. It’s also easy to forget
to make a connection.
I suggest that you print a copy of the schematic, and
each time you make a connection on the perforated
board, you eliminate that wire on your hardcopy, using
a highlighter. - Debris
When you’re trimming wires, the little fragments that
you cut don’t disappear. They start to clutter your work
area, and one of them can easily get trapped under
your perforated board, creating an electrical connec-
tion where you don’t want it.
This is another reason for working with something soft,
such as polyurethane foam, under your project. It tends
to absorb or hold little pieces of debris, reducing the
risk of you picking them up in your wiring.
Clean the underside of your board with an old (dry)
toothbrush before you apply power to it, and keep your
work area as neat as possible. The more meticulous you
are, the fewer problems you’ll have later.
Once again, be sure to check every joint with a magni-
fying glass.