How to Make Bi-Directional
by John Iovine
Flex sensors are passive resistive devices that can be used to detect bending or flexing.
Constructing commerical devices is not difficult, but does involve the use of specialty resistive
and conductive inks, silk screens to apply the inks, and specific heats to cure the inks — a little
too much manufacturing for most hobbyists. However, all is not lost, because there are simpler
sensors you can build. The flex sensor I will show you how to build here is a bi-directional flex
sensor that decreases its resistance in proportion to the amount it is bent.
The sensor we are building is
about 3/8” wide by 5” long. You can
easily make a sensor wider and longer
depending upon your application.
Flex sensors can be used in
robotics to determine joint movement
or placement. They can be utilized
as whiskers for wall detection. The
FIGURE 1. Flex sensor
50 SERVO 06.2009
sensors we will be making are also
pressure sensitive so they can be used
as either bumper switches for wall
detection or pressure switches on
For bio-metrics, the flex sensor
can be placed on a moving joint of
athletic equipment, for example, to
provide an electrical indication of
movement or placement. A few of the
sensors could be incorporated onto a
glove for a virtual reality application.
The materials needed for
construction of the bi-directional flex
sensor are shown in Figure 1.
Remember, the size of the materials
listed here is only a guideline to the
sensor we are constructing in this
article. These types of sensors can be
manufactured to larger widths and
•Copper foil laminate 1/4” x 4. 5”
•Acetate 1/4” x 4. 5” x .010 thick.
•Heat shrink tubing 3/8”
dia x 5”.
•Resistive material 5/16” x 5”
Copper foil laminate is used in the
electronics industry to make flexible
circuits. It is thin copper cladding on a
plastic material substrate like acetate.
The material we are using is single-sided copper: copper on one side and
the substrate (plastic) on the other.
FIGURE 2. Overview of flex sensor