What is a Force Sensitive Resistor?
FSR’s (Force Sensitive Resistors) are basically a resistor that changes its resistive value (in ohms Ω) depending on how much its pressed. These sensors are fairly low cost, and easy to use but they’re rarely accurate. They also vary some from sensor to sensor perhaps 10%. So basically when you use FSR’s you should only expect to get ranges of response. While FSRs can detect weight, they’re a bad choice for detecting exactly how many pounds of weight are on them…
Some basic stats
These stats are specifically for the Interlink 402, but nearly all FSRs will be similar. Checking the datasheet will always illuminate any differences
- Size: 1/2″ (12.5mm) diameter active area by 0.02″ thick
- Price $7.00 from the Adafruit shop
- Resistance range: Infinite/open circuit (no pressure), 100KΩ (light pressure) to 200Ω (max. pressure)
- Force range: 0 to 20 lb. (0 to 100 Newtons) applied evenly over the 0.125 sq in surface area
- Power supply: Any! Uses less than 1mA of current (depends on any pullup/down resistors used and supply voltage)
- Datasheet (note there are some mathematical inconsistancies in here)
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!)
We put together a MASSIVE tutorial on what they are, how to use them and example code for use with Arduino. You can view the tutorial here “FSR Force Sensitive Resistors are for squeezing!”.
…and pick’em up at the Adafruit store – Force-Sensitive Resistor (FSR).