Page 127 - Photodetection and Measurement - Maximizing Performance in Optical Systems

Useful Electronic Circuits and Construction Techniques to Get You Going

120 Chapter Six

components aimed at this need. With a hundred or so holes arranged
in an XY-array in a plastic brick, they have all the X axis rows connected
internally. The idea is that you insert the components and bridging wires more
or less in the Y direction, with the X connections taken care of internally. If you
use these, it is important to use solid-core connecting wires to allow easy inser-
tion. Stranded wire splays and either won’t go into the holes or goes in and
makes connections you don’t want.
However, the plastic blocks are not usually screened, and the large conduc-
tor strips attached to every point in the circuit can make for odd performance.
Wrapping aluminum foil around the block and grounding it with an alligator
clip can help, but I have never been very happy with this solution. On many
occasions I used to forget about the X-direction connections, with disastrous
results. They work better with digital logic ICs than with the variable packages
of analog components.
I have similar small accidents with copper strip board. This is insulating
material with a dense array of punched holes (usually on 0.1-inch centers), and
parallel strips of laminated copper foil, protected by a solderable lacquer. The
connections must be soldered for this. The ideas of using the board to make
the X-direction connections, leaving the Y direction for component leads and
wire bridges is similar to that of pluggable boards. At least here the hole and
component density is high enough to be useful, and once soldered the compo-
nents remain connected. You also have the option to sever the copper strips as
needed using a few turns of a handheld drill bit or the tool supplied for the job.
It is a big advantage to plan and draw out the circuit completely before start-
ing to solder. Even coarse graph paper or a word processor with a fixed char-
acter pitch font is suitable for this. As with pluggable boards, I generally forget
to sever a few lines, with results that are at best hard to understand. Reaming
out the little copper areas to isolate different regions of copper strip is also
fraught with risk; it’s easy to leave a few microscopic shards of copper to short
out power lines and clamp logic gates to one state. A good inspection under a
lensed desk lamp or low-magnification stereo microscope is beneficial. Most
layout problems are visible.
Years ago I used to spend hundreds of hours carefully laying out professional
printed circuit boards on a CAD system. These had to be photo-plotted on plastic
film, and then sent for transferring onto copper laminate board for subsequent
etching. This took several days but only took a couple of minutes to discover
that the circuit was seriously flawed. The throughput of this approach can be
limiting.
The approach that has lasted best with me is the use of blob board. This is
single-sided, copper-laminated composite board material, just like the strip
boards mentioned above, one of the family of Veroboard products. However,
instead of copper strips, this one has a predrilled array of isolated square copper
pads on 0.1-inch centers. In this case you have to make all the connections your-
self. With a small soldering iron, flux-cored solder, and a little practice, it is pos-
sible to quickly “draw” circuits in solder onto this blob board, bridging between
the copper islands.

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