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Flex Sensor 5.6 cm (Detect Bending Motion)

Posted by

Ekostra Electronics

April 11, 2025

On April 5, 2025

Flex Sensor 5.6cm

Bend Detection Sensor for Arduino and Wearable Electronics Projects

Introduction

The 5.6cm Flex Sensor is a variable resistor that changes resistance when bent. Perfect for detecting finger movements in gloves, robotic joints, or any application requiring bend measurement.

Key Features

🔄 Bend Sensing

10KΩ to 40KΩ resistance range

📏 Compact Size

5.6cm active sensing length

🔌 Simple Interface

Analog voltage output

👋 Wearable

Ideal for glove-based controls

Technical Specifications

Resistance Range	10KΩ (flat) to 40KΩ (90° bend)
Active Length	5.6cm (2.2 inches)
Width	6.4mm (0.25 inches)
Thickness	0.5mm (flat)
Bend Radius	12.7mm minimum
Operating Voltage	3.3V – 5V DC
Lifetime	1 million+ bends
Temperature Range	-35°C to +80°C

Pin Configuration

Wire Color	Description	Connection
Black	Ground	GND
Red	Signal	Analog Pin (with voltage divider)

Note: Requires a voltage divider circuit (10KΩ resistor recommended)

Basic Wiring with Arduino

// Voltage Divider Circuit:
// Flex Sensor → A0
// 10KΩ Resistor between A0 and VCC
// GND → Flex Sensor other terminal

Basic Bend Detection

const int flexPin = A0;

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

void loop() {
  int flexValue = analogRead(flexPin);
  Serial.print("Sensor Value: ");
  Serial.println(flexValue);
  
  if(flexValue > 800) {
    Serial.println("Fully Bent");
  } else if(flexValue > 500) {
    Serial.println("Partially Bent");
  } else {
    Serial.println("Flat Position");
  }
  
  delay(500);
}

Advanced Calibration

// Calibration values (adjust based on your sensor)
#define FLAT_RESISTANCE 10000  // 10KΩ when flat
#define BEND_RESISTANCE 40000  // 40KΩ when bent 90°
#define R_DIVIDER 10000        // 10KΩ resistor value

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

void loop() {
  int flexADC = analogRead(A0);
  float flexV = flexADC * 5.0 / 1023.0;
  float flexR = R_DIVIDER * (5.0 / flexV - 1.0);
  
  // Map resistance to bend angle (0°-90°)
  float angle = map(flexR, FLAT_RESISTANCE, BEND_RESISTANCE, 0, 90);
  angle = constrain(angle, 0, 90);
  
  Serial.print("Resistance: ");
  Serial.print(flexR/1000, 1);
  Serial.print("KΩ\tAngle: ");
  Serial.print(angle, 0);
  Serial.println("°");
  
  delay(500);
}

Calibration Tip: Record sensor values at known bend angles for best accuracy

Advanced Applications

Gesture Control

int lastFlexValue = 0;

void detectGesture() {
  int currentFlex = analogRead(A0);
  int delta = currentFlex - lastFlexValue;
  
  if(abs(delta) > 100) { // Threshold
    if(delta > 0) {
      Serial.println("Bending detected");
    } else {
      Serial.println("Straightening detected");
    }
  }
  lastFlexValue = currentFlex;
}

Multiple Sensors

const int numSensors = 5;
const int flexPins[] = {A0, A1, A2, A3, A4};

void readAllSensors() {
  for(int i=0; i<numSensors; i++) {
    int val = analogRead(flexPins[i]);
    Serial.print("Finger ");
    Serial.print(i);
    Serial.print(": ");
    Serial.println(val);
  }
}

Wireless Data

#include <SPI.h>
#include <nRF24L01.h>
#include <RF24.h>

RF24 radio(7, 8); // CE, CSN pins
const byte address[6] = "00001";

void setup() {
  radio.begin();
  radio.openWritingPipe(address);
  radio.setPALevel(RF24_PA_MIN);
  radio.stopListening();
}

void loop() {
  int flexData = analogRead(A0);
  radio.write(&flexData, sizeof(flexData));
  delay(20);
}