Stokes' ProjBlog

How to build a pressure sensor for (effectively) free April 1, 2009

NB: Despite the date, this actually works.

Andrew Sempere recently credited me for giving him an idea for a pressure sensor he’s currently using in a project. It was something I discovered accidentally, but further research revealed that the technique has been documented elsewhere. Regardless, I still think it’s pretty cool.

Basically, the conductive foam in which many ICs are shipped is, well, conductive. It has a high resistance, but that resistance decreases when the foam is compressed — in other words, a sort of primitive variable resistor. I used this property to create a basic pressure sensor. A small square of 1/4″ foam was placed between two wires, each of which had been bent into a tight zig-zag pattern. The very ends of each wire was bend inwards to create a little ‘tooth’ to help secure it in place. The whole thing was then wrapped in electrical tape. Total cost: incalcuably low, since most of the parts were either byproducts or too cheap to meter. The actual cost of materials is probably only pennies.

It’s definitely not a precision instrument, however. My tests (which I’ve since lost) showed a very noisy signal and the high and low values changed by several hundred ohms each trial. But, it would still work out great for applications that do not require precise measurements, like interactive art.

Now that I’ve been reminded of the project, I wonder if a basic positional sensor could be created by having a larger piece of foam with several wires on the bottom and a single layer of conductive material on the top. I’ll have to look into that.