The Force Sensitive Sensor, or Force Sensor-Resistor, as it is commonly referred to, are the sensors that detect, or track, physical stress, squeezing, or weight. They are conductive polymers (controlled through electricity) which are used through the application of force, and from there, sub-micrometre sized particles are formulated and touch the eletrodes to shift and change resistance (these sub-micrometre particles are all suspended in the film layer–which is where most of the electrode resistance and sensing occurs). Typically, these sensors only garner a range of pressure, detecting, instead of approximating the exact weight. It is said that FSR’s vary from sensor to sensor with a 10% margin. Conducting electrodes that manipulate resistance usually comes as a polymer sheet or ink, and are applied with screen printing (coating areas with some substance). The Resistor Pressure is measured in Ohms: the more pressure that is applied, the lower the resistance on the actual film is.
Presented here in this picture, is the Interlink 402 Model. On the right, the 402 Model’s interior is deconstructed. Between the flexible outer material, with a printed semi-conductor field, and the electrodes is a spacer adhesive, which acts as a sort of barrier and conductive controller of electrode flow. The over sensing-region is about a 1/2 diameter, while the entire resistor itself is 2.35 in. The overall thickness of the board is about 0.73 in., while the weight is roughly 0.01oz. Force Sensitive Resistors can also come in square shapes as well, but usually amount to the same conducting force.
While using an Arduino breadboard, the best way to apply a 402 Model is simply by plugging it in. Other ways consist of using clamp-style connectors (terminal blocks), or soldering onto the tabs (Soldering is the process of joining two or more objects together, through the process of melting and applying a filler jacket into a potential “joint”). Though they are very flexible and light in weight, the 402 Model is also made of very delicate material. In fact, most FSR models are very similar in power and cost (Interlink, as well as Sparkfun Electronics, Honeywell Sensing Productivity Solutions are responsible for creating them). Typically, a Force Sensitive-Resistor costs around $7.00, can sense force applied between 100g to 10kg, and are around 2-3 inches long.
In order to test how an FSR works, you can use a multimeter to connect to the resistance-measure mode. A multimeter’s measuring abilities range from continuity, resistance, voltage, and currents. Connecting the multimeter to the two tabs on an FSR Model helps show you how much the resistance changes.
To see a more in-depth way of how these resistors work, provided here are videos that walk you through this very concept:
