Gareth over on LetsMakeRobots has just recently demonstrated how to make a simple 3d printed touch sensor primarily using some conductive foam.
He has achieved this by utilizing the interesting, perhaps not well known properties of conductive foam. Conductive foam is widely known to be a great way of protecting your IC’s from static and often when receiving IC’s in the post they will be stuck into this foam. What many people don’t know about the foam however is the fact that it has some very interesting resistance properties.
Conductive foam acts as a resistor, not only a resistor, but a variable resistor, a variable resistor whose value depends on how much it is being ‘squished’.
Gareth has taken advantage of this property to create quite an accurate and repeatable pressure sensor system.
He uses two 3D printed parts as the body of the pressure sensor unit. Two contacts are placed at either end, he used small copper strips, with the conductive foam being placed between them.
The two 3D printed parts move inside each other, think of a hydraulic ram, compressing the conductive foam in between them.
All that is needed to turn this into a pressure sensor for something like an Arduino is to place it in a voltage divider setup with the output going to an Analog pin.
The idea is simple but the execution is ingenious. Even if you don’t have a 3D printer this system would be quite easy to replicate with a straw and toothpick perhaps.
You can download the 3D files from the Thingiverse page here.