How to use a Flex Sensor with Arduino Uno

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Last Updated on 22nd May 2023 by peppe8o

In this tutorial, we will use Arduino with a flex sensor to get the degree of bending.

Flex sensors are commonly used in applications such as robotics, gaming controllers, medical devices, and musical instruments to get information about twisting.

Introduction

A flex sensor is a type of sensor that can detect the amount of bending or deformation that occurs in a particular object or surface.

flex-sensor-02

Usually made of a flexible material, such as plastic or rubber, it is typically thin and lightweight and changes its resistance when it bends.

flex-sensor

Working principle of FLEX sensor

The flex sensor, also known as Flexible Potentiometer, is usually based on a phenolic resin substrate, a thin layer of conductive ink and a segmented conductor placed on top.

When the sensor is bent or flexed, the distance between the conductive strips changes and the conductive ink layer becomes thinner, causing the resistance of the sensor to increase. This change in resistance is proportional to the degree of bending or flexing of the sensor.

Image credits: https://www.sparkfun.com/datasheets/Sensors/Flex/flex22.pdf

Usually, an electronic circuit connected to the flex sensor measures the resistance and converts it into a corresponding electrical signal, whose intensity changes proportionally to the blending degree.

What We Need

Arduino Uno R3 board

As usual, I suggest adding from now to your favourite e-commerce shopping cart all the needed hardware, so that at the end you will be able to evaluate overall costs and decide if continue with the project or remove them from the shopping cart. So, hardware will be only:

Step-by-Step Procedure

Wiring Diagram of Flex sensor with Arduino

The figure shows the wiring diagram between the flex sensor, Arduino Uno, and LCD according to Arduino pinout. The resistor has a value of 1K-ohms and works as a voltage divider with the flex sensor.

Wiring diagram for Flex sensor and I2C LCD with Arduino Uno
Wiring diagram for Flex sensor and I2C LCD with Arduino Uno

The following table shows the patterns between the components of this project:

Flex SensorArduino UnoResistorI2C LCD
Pin 1 (right side)5VVCC
Pin 2 (left side)A0side 1
GNDside 2GND
A5SCL
A4SDA

Get the code and OLED Libraries

Connect your PC to Arduino and open Arduino IDE. For the very first steps, you can refer to Connecting Windows PC with Arduino tutorial. You can get the .ino code and libraries from my download area with the following link:

flex_sensor.ino

You also need to install the following libraries, according to my Install Arduino Libraries: methods to add libraries with Arduino IDE tutorial.

Library I2C LCD from the library manager
Library I2C LCD from the library manager

Code Explanation

Section 1: Before setup

This is the section before setup which we’ll use for global variables definition and libraries addition.

LiquidCrystal_I2C.h is the library for performing communication with LCD.

The I2C address, its rows count, and columns are defined.

We also define a variable to store the value of the A0 analogue input.

#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x26, 16, 2);
const int ADC_pin = A0;
int flex_ADC;

Section 2: Setup section

In the beginning, have defined the serial monitor with its baud rate.

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

The LCD is initialized, and its backlight is turned on.

  lcd.init();					
  lcd.backlight();

Cursors are set at (0, 0) pixels. The first print on the LCD will show the “peppe8o” label.

  lcd.setCursor(0,0);
  lcd.print("peppe8o");
}

Section 3: Loop section

In the loop section, we read the analogue value of the sensor and then map it, based on the resistance.

To know the mappings, you have to measure the flex resistance without connecting with the circuit. In this sensor case we have 30K-Ohm without bending, then (after fully bending) it’s 163 K-Ohms. After connecting the resistor with the sensor, the analogue value comes to be 6 to 33 mV.

void loop()
{
  flex_ADC = analogRead(ADC_pin);
  flex_ADC= map(flex_ADC, 6, 33, 163, 30);

Then after conversion, the sensor value will print on the LCD with its unit.

  Serial.println(flex_ADC);
  lcd.setCursor(0,0);          
  lcd.print("Resistance: "); 
  lcd.setCursor(0,1);           
  lcd.print(flex_ADC);
  lcd.setCursor(4,1);
  lcd.print("kohm");
  delay(500);
  lcd.clear();
}

Results

Firstly, you have to measure the resistance of the sensor. You can perform this task using a Multimeter set to measure resistance (or checking the raw analogue reading of your Arduino when attaching the flex sensor).

Based on the sensor unbending, the resistance for this tutorial will be a minimum 30 K-Ohm (it may vary depending on the sensor type). Then, after bending, the resistance increases up to 163K-Ohm:

The results display the output of the Flex sensor on the LCD. The no bend, bend to 90 degrees, bend to 120 degrees, then resulted in the full bending. As the sensor bent the resistance increases, and the maximum resistance increase to 163K-Ohms, while the minimum is 30 K-Ohms

Simulation 90-degree bend for Flex sensor and I2C LCD with Arduino Uno
Simulation 90-degree bend for Flex sensor and I2C LCD with Arduino Uno
Simulation 90-degree bend for Flex sensor and I2C LCD with Arduino Uno
Simulation 120-degree bend for Flex sensor and I2C LCD with Arduino Uno
Simulation full bend for Flex sensor and I2C LCD with Arduino Uno
Simulation full bend for Flex sensor and I2C LCD with Arduino Uno
Simulation no bend for Flex sensor and I2C LCD with Arduino Uno
Simulation no bend for Flex sensor and I2C LCD with Arduino Uno

What’s Next

Please find more tutorials on Arduino in peppe8o Arduino archives.

Enjoy!

Umar Jamil

For any queries and help for work, please contact me at:
Whatsapp: +92-346-661-7017/ Link
Email: umarjamil0007@gmail.com

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