Project tutorial
Pressure Pad Interfacing with Arduino

Pressure Pad Interfacing with Arduino

Glowing LED to detect the increase in pressure by pressure pad using Arduino.

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Components and supplies

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About this project

Pressure pads are designed to detect when pressure is applied to an area, and they come in a variety of quality and accuracy. The simplest pressure pads are often the equivalent of big switches. Inside a pressure pad are two layers of foil separated by a layer of foam with holes in it. When the foam is squashed, the metal contacts touch through the foam and complete the circuit.

This tutorial serves as a quick primer on rressure pads and demonstrates how to hook them up and use them with Arduino.

Code

PressurePad_LEDArduino
const int FSR_PIN = A0; // Pin connected to FSR/resistor divider
const int LED_PIN1 = 7;
const int LED_PIN2 = 6;
const int LED_PIN3 = 4;
const float VCC = 4.98; // Measured voltage of Ardunio 5V line
const float R_DIV = 3230.0; // Measured resistance of 3.3k resistor

void setup() 
{
  Serial.begin(9600);
  pinMode(FSR_PIN, INPUT);
  pinMode(LED_PIN1, OUTPUT);
  pinMode(LED_PIN2, OUTPUT);
  pinMode(LED_PIN3, OUTPUT);
}

void loop() 
{
  int fsrADC = analogRead(FSR_PIN);
  // If the FSR has no pressure, the resistance will be
  // near infinite. So the voltage should be near 0.
  if (fsrADC != 0) // If the analog reading is non-zero
  {
    // Use ADC reading to calculate voltage:
    float fsrV = fsrADC * VCC / 1023.0;
    // Use voltage and static resistor value to 
    // calculate FSR resistance:
    float fsrR = R_DIV * (VCC / fsrV - 1.0);
    Serial.println("Resistance: " + String(fsrR) + " ohms");
    // Guesstimate force based on slopes in figure 3 of
    // FSR datasheet:
    float force;
    float fsrG = 1.0 / fsrR; // Calculate conductance
    // Break parabolic curve down into two linear slopes:
    if (fsrR <= 600) 
      force = (fsrG - 0.00075) / 0.00000032639;
    else
      force =  fsrG / 0.000000642857;
    Serial.println("Force: " + String(force) + " g");
    Serial.println();
    if(force<10)
    {
       digitalWrite(LED_PIN1,LOW);
      digitalWrite(LED_PIN2,LOW);
      digitalWrite(LED_PIN3,LOW);}
    if(force>20)
    {
      digitalWrite(LED_PIN1,HIGH);
      digitalWrite(LED_PIN2,LOW);
      digitalWrite(LED_PIN3,LOW);
     
    }
    if(force>60)
    {
      digitalWrite(LED_PIN2,HIGH);
      digitalWrite(LED_PIN1,LOW);
      digitalWrite(LED_PIN3,LOW);
    }
    if(force>100)
    {
       digitalWrite(LED_PIN3,HIGH);
      digitalWrite(LED_PIN2,LOW);
      digitalWrite(LED_PIN1,LOW);
    }
  
    delay(500);
    
  }
  else
  {
    // No pressure detected
  }
}

Schematics

CircuitDiag
Fritzing example bb 2 hjdn0ytrp6

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