by Bryan Bergeron, Editor by Bryan Bergeron, Editor
Several years ago, I consulted on a project on body
area networks for the DoD. The idea was to create a
system of wearable sensors that would enable someone in
a distant command center to monitor the health of every
soldier in the field. The initial idea centered around a
watch and a satellite antenna embedded in a standard
military helmet. The project never gained traction, in part
because of the expense of the system, and in part
because of the weight/bulk burden placed on wearers.
Fast-forward to the present, and it’s imminently
possible for every hobbyist to afford a body area network
of their own. Miniature sensors are now affordable, easy
to work with, and reasonably accurate. Moreover, low
power, wearable processing power can be obtained off-the-shelf. For example, take the Arduino LilyPad, which I
bought from SparkFun Electronics ( www.sparkfun.com).
As shown in the accompanying photo, the two-inch
diameter disc carries a microprocessor, reset button, LED,
and assorted support components. More importantly, all
of the significant I/O ports and power are brought to the
periphery of the board, where the board can be
connected — via conductive thread — to sensors and
actuators. Instead of soldering, you tie a knot with the
silver-impregnated thread and connect the other end to a
sensor or other device. The beauty of using thread and a
sewing needle instead of wire and solder is that the disc
can be embedded without fear of the connections
breaking due to stress on copper wires. I was first drawn
to the LilyPad because it could withstand the elements.
The LilyPad can be washed, as can the conductive thread.
I haven’t washed either, but I have no doubt both would
withstand at least a quick rinse in the shower. There is
some talk on the Web suggesting some of the silver in the
thread can be washed out, so don’t get overly vigorous.
If you’ve worked with any incarnation of the Arduino,
then you know the LilyPad. However, the conductive
thread is another matter. It lends itself to all sorts of
projects, while presenting new circuit design challenges.
For example, once you start working with the non-insulated conductive thread, you’ll appreciate the PVC
jacket on ordinary wire. With conductive thread, even a
simple circuit becomes a traveling salesman problem.
There are simple tricks of keeping separate threads
electrically isolated, such as placing stitching on opposite
sides of the cloth substrate. When all else fails, I resort to
pushing a needle and thread through the PVC insulation.
There’s a penalty in terms of flexibility over the raw
conductive thread, but it’s minor.
I’ve used the thread to create pressure sensors (run
two pieces of conductive thread in parallel through
carbon-impregnated foam), to provide super-flexible
wiring to sensors embedded in a haptic glove, and to
create surface sensors in a shirt designed to pick up
cardiac electrical activity for an electrocardiogram (EKG)
monitor. I’m sure you can think of additional uses for a