This force-sensing resistor (FSR) from Interlink Electronics is a passive component that exhibits a decrease in resistance when there is an increase in the force applied to the 0.28″-diameter (0.5 cm) active area, allowing you to create a sensor that is able to detect force or pressure. With a force sensitivity range of a few grams to a few kilograms, this sensor is optimized for use in human touch control applications.
In our tests, the resistance exceeded 1 MΩ with no applied pressure and ranged from around 100 kΩ to a few hundred Ohms as finger pressure varied from light (a few dozen grams) to heavy (pressing as hard as possible). The resistance is very stable when the pressure is fixed, and the readings are very repeatable (there are no problems with hysteresis). This resistance range is well suited to work directly with the internal pull-ups of many microcontrollers such as AVRs and PICs. The FSR was responsive enough and sensitive enough to distinctly pick up light, rapid finger taps, and it was even able to pick up the vibrations of a small vibration motor placed on it on the motor’s side.
The 0.2″-diameter circular pad is flexible, light (0.25 g), and extremely thin (0.02″), and it has a circular active sensing area with a diameter of 0.58″. It does not appreciably compress when pressure is applied, and it has a masked adhesive backing for easy mounting. The FSR has two male pins (called “solder tabs”) spaced 0.1″ apart, which means they are compatible with most solderless breadboards and perfboards, though the solder tabs are too short to work well with many 0.1″ connectors. (A very similar FSR with a much longer tail is also available; see the picture on the right for a side-by-side comparison of the two versions.)