How to Use the op-amp Op-Amp to Improve FSR Signal Stability

What’s the Problem?

When using a Force Sensitive Resistor (FSR) in a voltage divider circuit, you might notice the analog signal fluctuates, especially at low force levels or over long wires. This makes it difficult to get consistent results.

The issue often comes from loading effects caused by the Arduino’s analog input. A simple way to fix this is by adding a buffer op-amp like the op-amp.

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What’s a Buffer and Why Use It?

A buffer, also known as a voltage follower, is a circuit where the output exactly follows the input. While it doesn’t amplify the signal, it isolates the voltage divider from whatever comes next.

Main benefits:

• Prevents signal distortion from input loading
• Reduces noise and jitter
• Stabilizes low-force readings
• Improves accuracy for multi-sensor systems

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Circuit Diagram: FSR + op-amp Buffer

Your FSR voltage divider stays mostly the same. Here’s how to wire the op-amp:

  +5V
   |
  [FSR]
   |
   +----> Point A ----> op-amp non-inverting input (+)
   |
 [10kΩ resistor]
   |
  GND

op-amp wiring:
- +IN → Point A (divider output)
- −IN → op-amp output (feedback loop)
- OUT → Arduino A0
- VCC → 5V
- GND → Ground

This configuration creates a voltage follower circuit using one channel of the op-amp.

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Arduino Code Example + Resistance Calculation

Once connected, your code stays simple:

const int fsrPin = A0;
const float Vcc = 5.0;
const float R_fixed = 10000.0; // 10kΩ

void setup() {
  Serial.begin(9600);
}

void loop() {
  int val = analogRead(fsrPin);
  float voltage = val * Vcc / 1024.0;
  Serial.print("FSR Voltage: ");
  Serial.println(voltage, 2);

  // Calculate FSR resistance using voltage divider formula
  if (voltage > 0.01) { // Avoid division by zero
    float fsrResistance = (Vcc - voltage) * R_fixed / voltage;
    Serial.print("FSR Resistance: ");
    Serial.print(fsrResistance);
    Serial.println(" ohms");
  }
  else {
    Serial.println("FSR Resistance: Infinite (no pressure)");
  }

  delay(500);
}

This example prints both the voltage and the calculated resistance of the FSR, giving you deeper insight into its behavior under different pressure levels.

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Suggested Components

Resistor (R_fixed):

• 10kΩ → general-purpose
• 2.2kΩ → heavy force sensitivity
• 47kΩ → light touch sensitivity

Op-amp:

• op-amp (dual op-amp, 5V single supply)
• Widely available and low cost

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When Should You Use a Buffer?

Use this op-amp setup when:

• Your readings fluctuate too much
• You need more consistent force detection
• You plan to scale up to multiple sensors
• You want to improve low-force resolution

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Conclusion

Adding an op-amp op-amp as a voltage buffer is a straightforward and cost-effective way to improve the performance of your FSR-based circuits. By stabilizing the output of the voltage divider and protecting it from input interference, you gain more reliable and precise analog readings—especially important in applications involving low force detection or multiple sensors.

Whether you're building a prototype, refining a commercial device, or simply looking to improve measurement accuracy, incorporating a buffer is a valuable enhancement. This small modification can make a big difference in how your FSR responds and performs in the real world.