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A Force Sensitive Resistor (FSR) is a type of sensor used to measure the force or pressure applied to a surface. FSRs are often used in applications where detecting touch, pressure, or force is important. They are commonly found in various consumer electronics, medical devices, and interactive systems.

Key Features:

1. Measurement Principle:

   • Resistance Change: FSRs operate based on the principle of variable resistance. When force is applied to the sensor, its resistance decreases, and this change can be measured electrically.
   • Pressure Sensitivity: The resistance of the FSR decreases as the force or pressure increases, making it possible to estimate the applied force.

2. Construction:

   • Flexible Substrate: The sensor is typically made from a flexible, thin material that can be easily integrated into various surfaces.
   • Conductive Layers: FSRs consist of a conductive layer that changes resistance under pressure. This layer is sandwiched between two electrodes.
   • Terminals: Electrical terminals at the ends of the sensor allow for connection to measurement or control systems.

3. Output Type:

   • Analog Output: FSRs generally provide an analog resistance output. The resistance varies with the amount of force applied, which can be measured as a voltage drop in a voltage divider circuit.
   • Non-linear Response: The relationship between force and resistance is non-linear, so calibration may be required to interpret the readings accurately.

Types of FSRs:

1. Standard FSRs:

   • Pressure Range: Designed to measure a wide range of pressures from light touch to significant force.
   • Applications: Used in various applications, including touch sensors, pressure mapping, and force measurement.

2. High-Pressure FSRs:

   • Pressure Range: Optimized for measuring higher forces or pressures.
   • Applications: Suitable for applications where high pressure needs to be accurately measured.

Example of a Standard FSR (e.g., FSR402):

Specifications:

• Resistance Range: Typically from a few kilo-ohms (kΩ) without pressure to a few ohms under maximum pressure.
• Pressure Sensitivity: Varies depending on the specific sensor model.

Wiring and Usage:

1. Wiring Diagram:

   • Power Supply: Connects to a voltage source (e.g., 5V).
   • Output Connection: The output is taken from a voltage divider circuit connected to the FSR.

// Pin definition
const int flexPin = A0;  // Analog pin connected to the flex sensor

// Thresholds for gesture recognition
int flexReading = 0;
int flexThresholdLow = 300;  // Threshold for low bend (e.g., relaxed hand)
int flexThresholdHigh = 700; // Threshold for high bend (e.g., full hand bend)

// Define hand gesture states
enum Gesture {
  RELAXED,
  BENT,
  FULL_BEND
};

Gesture currentGesture = RELAXED;  // Initialize to relaxed hand position

void setup() {
  Serial.begin(9600);  // Start serial communication
}

void loop() {
  // Read the flex sensor value (voltage divider output)
  flexReading = analogRead(flexPin);
  
  // Print the raw sensor value to the serial monitor
  Serial.print("Flex Sensor Reading: ");
  Serial.println(flexReading);
  
  // Determine hand gesture based on the flex sensor reading
  if (flexReading < flexThresholdLow) {
    currentGesture = RELAXED;  // Hand is in a relaxed position
  } else if (flexReading >= flexThresholdLow && flexReading < flexThresholdHigh) {
    currentGesture = BENT;     // Hand is partially bent
  } else {
    currentGesture = FULL_BEND; // Hand is fully bent (close fist)
  }

  // Output the detected gesture
  switch (currentGesture) {
    case RELAXED:
      Serial.println("Gesture: Relaxed Hand");
      break;
    case BENT:
      Serial.println("Gesture: Bent Hand");
      break;
    case FULL_BEND:
      Serial.println("Gesture: Full Bend Hand");
      break;
  }

  delay(100);  // Delay for stability and serial printing
}