Force Sensing Resistors were invented in 1977 by Franklin Eventoff, the man who would later, in 1985, go on to found Interlink Electronics, a key global manufacturer of FSRs for whom we are the sole UK distributer.
Force Sensing Resistors, or FSRs as they tend to be known, are constructed of a pair of polymer layers, held a hairsbreadth apart. One layer contains printed electrodes, and the other is covered by a conductive surface, so when pressure is applied to the FSR, the two layers meet, resulting in a variable resistance based on the amount of pressure applied.
In the forty years since they were invented, Force Sensing Resistors have found use in many different industries around the globe, jumping from the food industry, to the medical profession, through to musical instruments, and pretty much everywhere in between. Even in just one of these industries, the use of FSRs is widely different. For example, in the medical profession, Force Sensing Resistors are used to create mats that lie on beds, to allow nurses to know if someone has accidentally slipped off, or even moved. The same FSRs are also used to control prosthetic limbs, and have even been converted into shoes to help teach people how to walk again.
With six different models, the Force Sensing Resistors from Interlink Electronics are available to cover just about any niche you can think of, and their tiny cross section of about half a millimeter means they can be concealed in practically any surface, granting that surface area the ability to control whatever it is you have your FSRs connected to.
Force Sensing Resistors come in several shapes and sizes. With the smallest active surface area being just 5mm across, you can fit the FSR400 into just about any application. There is also available a larger circle, the FSR402. Both types are available with either a long or short tail attached to them which run out to solder tags. Going larger still, you have the FSR406, a square that is perfect for working into an array, and the FSR408, a long strip which can be cut down to size.
I can think of only three products launched in 1977, the Force Sensing Resistor, the Post-It Note, and the movie, Star Wars. It must have been a good year, since all three of these went onto bigger and better things.