A force sensing resistor is a sensor used to measure the force (like pressure, squeezing, grip or weight) applied by detecting the resistance variation caused by the pressure.
The FSR technology was invented and patented by Franklin Eventoff in 1977. He found a special type of conductive polymer could change resistance under the pressure applied to its surface.
The sensing element is one or multiple layers of special thin film material that is applied to a flexible substrate. When a force is applied to the structure, the thin film bends thus it causes the resistance decreases. The amount of resistance change is the function of the pressure applied to the thin film. When the pressure is removed, the thin film returns to its equilibrium position and the resistance value resets. After the Force-Sensing Resistor is accurately calibrated, it can be used to measure the force precisely.
As the technology of materials advances, FSR sensors become more accurate and we have found more applications of FSR sensors.
- Up/Down or Increase/Decrease control of force or speed;
- Musical instrument controls;
- Human Machine Interface;
- Hand tool motor speed control;
- Robotic finger grip control;
- Seat / Bed occupancy detection;
Ohmite FSR series Force-Sensing Resistors sensors have just been carried by Mouser aiming at the applications for airbag controls, Human-Machine Interface and Machine-machine interface controls. The FSR series FSR sensors are provided in three different designs, square (FSR01CE), circle (FSR02CE) and strip (FSR03CE). This Ohmite resistor series includes a pigtail extending on one end with an industry-standard connector. Each sensor of FSR series has a force range of up to 5kg.
A FSR sensor can be considered as a variable resistance device and can be used in voltage divider application of FSR sensor.
Vout = RREF x VREF / (RREF + RFSR)
The output voltage is therefore the function of the variable resistance of the FSR sensor under the changing pressure applied to the device.