Using the circular knitting machine to knit a circular tube with the Schoeller 50/2 conductive yarn, makes for an excellent stretch sensor that can be used (among other things) to capture the pressure of a balloon inflating and deflating.

Closeup of knit yarn, where the red yarn is regular yarn and the gray wide center stripe is conductive.

You can also knit the conductive yarn alongside a regular yarn, this increases resistance. Below are pictures of an example where the thin gray conductive yarn is knit along side regluar white yarn using the circular knitting machine.

Circular knitting machines are cheap and can be ordered via Amazon online. With them you can knit both tubes and square pieces and knitting larger pieces is a matter of minutes. But you can not gauge that spacing between the needles, so when working with thinner yarns, the knit is very loose. Circular knitting machines come in different sizes with different needle spacing. The left picture bellow is of a Singer circular knitting machine that has 20 needles and about 20cm diameter. The right picture bellow is of a Addi Express Kingsize circular knitting machine that has 46 needles and about 35cm diameter.

Stretch Sensing Video

Inflation Sensing Video