The materials needed for the construction of the bi-direction flex sensor is shown in figure 1 and listed below. The size of the materials listed is only a guideline to the sensor we are constructing in this article. These types of sensors can be manufactured to larger widths and lengths.
- Copper foil laminate ¼" x 4.5" (see text)
- Acetate ¼" x 4.5" x .010 thick
- Heat shrink tubing 3/8" dia x 5"
- Resistive material 5/16" x 5" (see text)
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, The copper cladding material is cut into two pieces ¼" wide x 4.5" long strips. The material is easily cut with a scissors. Solder about 6" of wire to one end of each strip. You may fine it easier to solder the wire to the strip if you tin the bottom 3/8" of each strip. Solder each wire to one corner side of the strip. It doesn’t matter which side you choose, just make sure you solder both strips on the same side, see figure 2.
There are a variety of resistive materials available; cloth, plastic and paper. The common element of all the appropriate
materials is that the material is somewhat conductive or resistive. The degree to which the material is resistive will
determine the scale at which your flex sensor operates.
For the example here I am constructing here, I using conductive black plastic poly bags conductive bags used in the
electrical industry. These bags are used to store components that are static sensitive. The bags are made from single layer
of carbon-loaded polyethylene and its conductivity does not depend on humidity. I cut the bags into the 3/8
" wide by 5" long strips.