FSR
Reports applied force as a 1 MΩ → 1 kΩ resistance swing across a thin (<0.5 mm) flexible pad — readable as a simple voltage divider with a fixed pull-up resistor and an MCU's ADC.
Two flexible polymer sheets carry interdigitated conductive-ink electrodes on the active sheet and a semiconductive 'force-ink' coating on the spacer side. Without pressure, only point contacts touch and resistance is high. Press the pad and the contact area between the two layers grows, reducing resistance with a roughly logarithmic force-vs-conductance curve.
In plain terms
Like a sponge that conducts electricity better when squeezed — gentle press, weak current; hard press, strong current; in between, a smooth analog 'how hard?'.
Why designers use it
- Cheap and easy — a 25 mm round Interlink FSR plus one resistor reads force on any GPIO ADC pin.
- Static-force friendly — unlike piezo sensors, FSRs respond to held pressure, not just transients.
- Conformable — wrap onto curved surfaces, fingertips, and footbeds where rigid load cells won't go.
- Low parts count — one FSR pad replaces a discrete force gauge plus signal conditioning IC for hobby and consumer use.
Best for
- MIDI pads
- Insole pressure
- Hobby robotics
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- When you need ±1 % accuracy or temperature stability — FSRs drift with temperature and creep under sustained load.
- For precision weighing or load measurement — pull a strain-gauge load cell instead.
Common mistakes
- Calibrating once and trusting it forever — FSR resistance creeps under static load, so calibration in-app each session is required.
- Routing the FSR through a long unshielded ribbon cable — capacitance to ground biases the divider and the press feels 'mushy'.
Where you will find it
- An Akai MPK Mini drum-pad controller uses 16 FSR pads beneath silicone caps: each pad's resistance change feeds into a Microchip PIC18F46K22 MCU's ADC, which translates press hardness into MIDI velocity at sub-1 ms latency for live performance.
- A Tekscan FlexiForce A201 sensor strapped to a Kuka KR3 robot's gripper jaw lets a research lab control grasp force on fragile objects: the FSR's 0–110 N range and 1.5 % linearity over its mid-range envelope is exactly enough for picking strawberries without bruising.
- A Nike Adapt BB self-lacing basketball shoe uses an FSR insole sensor to detect when the user steps in, triggering the lacing motor without a button press: the FSR's flat profile fits between forefoot pads where a load cell wouldn't.
A short history
A force-sensitive resistor changes resistance when force is applied to its sensing surface. Conductive-polymer constructions commonly reduce resistance as pressure brings conductive regions into closer contact. Their thin form is useful for pressure-sensitive controls, but the sensor's response must be characterised for the intended measurement.