The FSR400 force sensor is a compact, flexible force-sensing resistor designed to convert applied pressure into a measurable electrical signal through changes in resistance. This article will discuss the FSR400 force sensor schematic operation, typical force curve, pinout details, equivalent models, specifications, and more.

Catalog

FSR400 Force Sensor Overview

The FSR400 force sensor is a thin and flexible force-sensing resistor designed to detect changes in pressure through variations in electrical resistance. When force is applied to its surface, the resistance decreases, allowing electronic systems to measure touch or press intensity in a simple and effective way.

Built using polymer thick film (PTF) technology, the FSR400 is lightweight, durable, and suitable for repeated use. It is a single-zone sensor with a compact round sensing area measuring 7.62 mm in diameter. This design makes it easy to integrate into space-limited devices while maintaining reliable force response.

Developed by Interlink Electronics, the FSR400 can also be customized in different sizes, tail lengths, and connector options to meet specific design needs.

FSR400 Force Sensor Pinout Details

FSR400 Alternatives & Equivalent Models

• FSR402

• FSR404

• FSR406

• FSR408

• FSR410

• FSR412

• FSR414

• FSR416

• FSR418

• FSR420

FSR400 Force Sensor Schematic Diagram

The schematic shows the FSR400 Force Sensor used in a simple voltage-divider and signal-buffer configuration. The FSR is connected between the supply voltage (V+) and a fixed resistor (RM) that goes to ground. Together, the FSR and RM form a voltage divider where the midpoint voltage changes based on the force applied to the sensor.

When no force or light force is applied, the FSR has a high resistance, resulting in a lower voltage at the divider node. As force increases, the resistance of the FSR decreases, causing the voltage at the midpoint to rise. This varying voltage represents the applied force in electrical form.

The operational amplifier is configured as a voltage follower (buffer), with its output connected directly to the inverting input. This setup does not amplify the signal but provides a stable output (VOUT) with low output impedance. As a result, the force-dependent voltage can be safely read by an ADC or control circuit without loading or affecting the sensor behavior.

FSR400 Typical Force Curve

The FSR400 Typical Force Curve shows the relationship between applied force and sensor resistance on a logarithmic scale. As the force applied to the sensor increases, the resistance decreases rapidly at first and then more gradually. This nonlinear behavior is characteristic of force-sensing resistors and highlights that the sensor is more sensitive at lower force levels.

At light forces, a small increase in pressure causes a large drop in resistance, making the FSR400 effective for detecting touch and low-force inputs. As force continues to increase, the rate of resistance change slows down, indicating reduced sensitivity at higher loads. This means the sensor is best suited for relative force measurement rather than precise weight measurement.

FSR400 Force Sensor Specifications

FSR400 Force Sensor Features

• Low Actuation Force – Detects force starting from as low as 0.1 N, making it suitable for light touch sensing.

• Wide Force Sensitivity Range – Responds across a broad force range, allowing flexible force detection levels.

• High Repeatability – Provides consistent force readings with repeatability as low as ±2% under controlled conditions.

• Customizable Size Options – Available in various sizes and shapes to match different mechanical designs.

• Ultra-Thin Profile – Thin construction (around 0.35 mm) enables easy integration into compact assemblies.

• High Durability – Designed to withstand up to 10 million actuations without performance failure.

• Cost-Effective Solution – Offers reliable force sensing at a low overall system cost.

• Easy Integration – Simple two-terminal design allows straightforward connection to standard circuits.

How to Utilize FSR400 Force Sensor

The FSR400 force sensor works as a variable resistor whose resistance changes in response to applied pressure. When no force is applied, the sensor’s resistance is very high, and as pressure increases, its resistance drops. Because most electronic systems read voltage rather than resistance directly, the sensor is commonly used in a voltage divider circuit to convert this resistance change into a measurable voltage signal.

In the circuit diagram, the FSR400 is connected in series with a fixed resistor (R1) between the supply voltage (VCC) and ground. The output voltage (Vo) is taken from the junction between R1 and the FSR. This midpoint voltage depends on the ratio between the fixed resistor and the sensor’s resistance. When the sensor is not pressed, its high resistance causes Vo to remain relatively high. As force is applied and the sensor resistance decreases, the voltage at Vo drops accordingly.

This varying output voltage represents the applied force and can be fed directly into an analog-to-digital converter (ADC) of a microcontroller. By monitoring changes in Vo, the system can reliably detect and compare different pressure levels applied to the FSR400.

Interfacing FSR400 Force Sensor w/ Arduino

The diagram shows how the FSR400 force sensor is connected to an Arduino using a simple voltage-divider setup. One terminal of the FSR400 is connected to the 5V supply from the Arduino, while the other terminal is connected to a fixed resistor that goes to ground. This arrangement converts the sensor’s changing resistance into a changing voltage.

The junction between the FSR400 and the fixed resistor is connected to one of the Arduino’s analog input pins. When no force is applied, the sensor has high resistance, resulting in a higher voltage at the analog pin. As pressure is applied to the sensor, its resistance decreases, causing the voltage at the analog input to drop.

The Arduino reads this changing voltage using its analog-to-digital converter (ADC) and converts it into a numeric value. This value can then be used in code to detect touch, measure relative force, or trigger actions based on pressure levels applied to the FSR400.

FSR400 Force Sensor Applications

• Touch-sensitive buttons

• Pressure-sensitive switches

• Human–machine interface controls

• Robotics force feedback

• Grip force detection

• Medical device touch inputs

• Wearable electronics

• Industrial control panels

• Consumer electronics input sensing

• Load and contact detection

Mechanical Dimensions

Conclusion

The FSR400 force sensor is useful for detecting touch and relative force in electronic systems. By operating as a variable resistor, it allows pressure changes to be easily converted into voltage signals using simple voltage-divider circuits and read by microcontrollers such as Arduino. Its nonlinear force response, high durability, and compact size make it well suited for human–machine interfaces, robotics, medical devices, and consumer electronics.