How to measure force/pressure with an FSR
As we've said, the FSR's resistance changes as more pressure is applied. When there is no pressure, the sensor looks like an infinite resistor (open circuit), as the pressure increases, the resistance goes down. This graph indicates approximately the resistance of the sensor at different force measurements. (Note that force is not measured in grams and what they really mean is Newtons * 100!)(See graph below)
Its important to notice that the graph isn't really linear (its a log/log graph) and that at especially low force measurements it quickly goes from infinite to 100K ohms.Testing your FSR
The easiest way to determine how your FSR works is to connect a multimeter in resistance-measurement mode
to the two tabs on your sensor and see how the resistance changes. Because the resistance changes a lot, a auto-ranging meter works well here. Otherwise, just make sure you try different ranges, between 1M ohms and 100 ohms before 'giving up'.Connecting to your FSR
Because FSRs are basically resistors, they are non-polarized. That means you can connect them up 'either way' and they'll work just fine!
FSRs are often a polymer with conductive material silk-screened on. That means they're plastic and the connection tab is crimped on somewhat delicate material. The best way to connect to these is to simply plug them into a breadboard
or use a clamp-style connector like alligator clips (see image below)
, female header
or a terminal block such as Phoenix #1881448
It is possible to solder onto the tabs but you must be very fast because if your iron is not good quality or you dally even a few seconds, you will melt the plastic and ruin the FSR! Don't attempt to solder directly to your FSR unless you are absolutely sure you have the skills to do so.