FIGURE 12. Pre-cut wire wrap wire.
FIGURE 13. Spooled wire wrap wire.
sizes (diameters). The most common insulation is “kynar,”
a registered trademark of Pennwalt Corporation. This is pre-cut
wire (see Figure 12) in various standard lengths, insulations,
and colors, and also rolls (see Figure 13). It has one inch
of stripped insulation on each end. It is an AWG 30 gauge
silver-plated soft copper wire insulated with a fluorocarbon
that does not emit dangerous gases when you heat it.
Discrete component holders (headers) and IC sockets
with wire wrap pins are also found (see Figure 14). You
can place these labels on the underside of an IC to help
to quickly identify pins since you are looking at the IC or
component from its underside. (If you suffer from
spatial orientation problems or dyslexia, this is especially
helpful.) Flat, interconnecting ribbon cables and other
interconnecting interfacing connectors having wire wrap
pin terminations are also available.
The Motivating Factors
Hobbyists have become more sophisticated and
exposed to more numerous electronic products. This method
allows you to repeatedly wire and rewire any circuit to
change and/or experiment with (e.g., an IC’s characteristics).
The use of proto boards also has its place; however, wire
wrapping tends to be more permanent because of its
resistance to vibration and other abuse, as previously
mentioned. Also, proto boards eventually will suffer contact
wear after prolonged use, whereby the contacts no longer
hold the wire tightly and present an added unforeseen
resistance. Proto boards can also suffer from using too large
a wire that springs their contacts. Wire wrap boards will last
forever if you properly care for them by not applying lateral
force to the pins. You’ll break them off if you repeatedly
bend them over and straighten them too many times.
In small engineering development labs or within
hobbyist workshops, computer driven wire wrappers
do not exist (see Figure 15). Usually the wrapping tool
looks like a fat pencil and does wrapping on one end,
unwrapping on the other, and has a slit in which to place
the wire. The wire is then given a quick tug, stripping away
the insulation. There is a middle ground of sophistication
with electric, handheld guns that now even have bits that
automatically strip away the insulation to a predetermined
length. You simply press the trigger which twirls the bare
wire around the post.
AWG American Wire Gauge
Hobbyist’s wrap wire is almost always 30 gauge or
30 AWG. The AWG stands for American Wire Gauge
and #30 ASA has a 100.5 circular mil cross-sectional area.
This determines wire resistance and its current carrying
capability. A general approximation is that for each three
numbers you go down in the AWG chart, you experience
a doubling in cross-sectional area. So, you would expect a
#27 wire to have twice the cross-sectional area of a #30
FIGURE 14. Pin identifiers from
eight to 40 pin DIPs that go
directly under the IC you wrap.
FIGURE 15. A
June 2009 49