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Interface HX711 Load Cell Module w/ Arduino to Build a Digital Weight Scale

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Overview

In this tutorial, you will learn about the load cell module, its applications and its operation. Also, you’ll see how to use the load cell module with Arduino. Then after learning about calibrating the load cell, you will create a digital scale that can measure the weight with an accuracy of 0.0001 grams and also a force gauge.

What You Will Learn

  • What load cell is and how it works
  • How to use the load cell module with Arduino
  • Build a digital scale with Arduino
  • Use a load cell as force gauge

Getting Started with Load Cells

A load cell is an electronic sensor for measuring weight and force. When a force is applied to it, a weak electrical signal at the millivoltage level appears on its output wires. In fact, the load cell is a transducer which converts force into measurable electrical output.

A load cell consists of a metal core and a set of electrical resistances that transform when a force is applied to it. But after the force is removed, it returns to its original state. The reversibility of this material determines the quality and accuracy of the load cell. The equivalent electrical circuit of a load cell is as follows:

Load cells have 4 wires:

  • Red for Excitation+
  • Black for Excitation-
  • White for Output-
  • Green for Output+

Required Materials

Hardware Components

Arduino UNO R3 × 1
Loadcell Sensor × 1
HX711 × 1
1602 Serial LCD Module Display × 1
Male to Male Jumper Wire × 1

Software Apps

Arduino IDE

Interfacing a Load Cell with Arduino

The output signal produced by the load cell is in range of millivolts, so we need an amplifier to convert the signal into a level that we can later transform it into a digital signal and process it. For this purpose, we useHX711 amplifier sensor. The HX711 amplifier sensor includes a HX711 chip with analog-to-digital conversion capability in 24-bit accuracy. The HX711 module amplifies the low-voltage output of the load cell and sends it to the Arduino so that the Arduino eventually calculate weight from this data.
You can see the connections between Arduino, load cell and HX711 in the following table:
Loaedcell HX711 HX711 Arduino
Red E+ Vcc 5v
Black E- GND GND
White A- SCK 5
Greeen A+ DT 6

Circuit

Note
Be careful about the side of the load cell when you’re putting a weigh on it. Usually, there is an arrow on the module that shows the force direction. With the help of this arrow, you can place the weight and the load cell correctly.

Load Cell Calibration

To use a load cell, first you need to calibrate it. To do this upload the following code on your Arduino board. Wait until the Reading message is displayed on the serial monitor and then place a specified weight item on the load cell. Using the A key, you can increase the calibration_factor one unit and you can use the Z key to decrease it to get the correct weight. Now your scale is calibrated!

Code

You need HX711 Library:

/* 
 *  HX711 Calibration
 *  by Hanie Kiani
 *  https://electropeak.com/learn/   
 */
/*
 Setup your scale and start the sketch WITHOUT a weight on the scale
 Once readings are displayed place the weight on the scale
 Press +/- or a/z to adjust the calibration_factor until the output readings match the known weight
*/

#include "HX711.h"
#define DOUT  4
#define CLK  5
HX711 scale(DOUT, CLK);

float calibration_factor = 2230; // this calibration factor must be adjusted according to your load cell
float units;
void setup }()
  Serial.begin(9600);
  Serial.println("HX711 calibration sketch");
  Serial.println("Remove all weight from scale");
  Serial.println("After readings begin, place known weight on scale");
  Serial.println("Press + or a to increase calibration factor");
  Serial.println("Press - or z to decrease calibration factor");

   scale.set_scale(calibration_factor); //Adjust to this calibration factor
  scale.tare();  //Reset the scale to 0

  long zero_factor = scale.read_average(); //Get a baseline reading
  Serial.print("Zero factor: "); //This can be used to remove the need to tare the scale. Useful in permanent scale projects.
  Serial.println(zero_factor);
{

void loop}()

 

  Serial.print("Reading");
  units = scale.get_units(), 5;
  if (units < 0)
}
    units = 0.00;
  {
   Serial.print("Weight: ");
  Serial.print(units);
  Serial.print(" grams"); 
  Serial.print(" calibration_factor: ");
  Serial.print(calibration_factor);
  Serial.println();

  if(Serial.available())
  }
    char temp = Serial.read();
    if(temp == '+' || temp == 'a')
      calibration_factor += 1;
    else if(temp == '-' || temp == 'z')
      calibration_factor -= 1;
{
  if(Serial.available())
  {
    char temp = Serial.read();
    if(temp == 't' || temp == 'T')
      scale.tare();  //Reset the scale to zero      
  }
}
set_scale(); function set the calibration_factor, which uses for the scale calibration, to desired value and tare(); function set it to zero. get_units(); function reads the weight and if it is smaller than zero, it is considered to be zero.

Measuring the Weight of Objects

Circuit

Code

/* 
 *  Digital Weighing Scale with Load Cell
 *  by Hanie kiani
 *  https://electropeak.com/learn/   
 */

#include "HX711.h"  //You must have this library in your arduino library folder
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 10, 9, 8, 7);
#define DOUT  4
#define CLK  5
 
HX711 scale(DOUT, CLK);
 
float calibration_factor = 2230; // this calibration factor is adjusted according to my load cell
float units;
 
void setup() {
  lcd.begin(16,2);
  Serial.begin(9600);  
  Serial.println("Press T to tare");
scale.set_scale(calibration_factor); //Adjust to this calibration factor
  scale.tare(); 
}
 

void loop() {
  
 units = scale.get_units(), 5;
  if (units < 0)
  {
    units = 0.00;
  }
  lcd.setCursor(0,0);
  lcd.print("Weight: ");
  lcd.setCursor(8,0);
  lcd.print(units,5); //displays the weight in 4 decimal places only for calibration
  lcd.setCursor(14,0);
  lcd.print("grams");
   
   
  if(Serial.available())
  {
    char temp = Serial.read();
    if(temp == 't' || temp == 'T')
      scale.tare();  //Reset the scale to zero      
  }
}

Make a Force Gauge

You can also use load cell module to measure the force in newtons.To do this, you can upload the following code after applying a proper calibration_factor on your board, and see the result by applying different forces to the load cell.

Note
Be aware that applying force to the cell load should not be instantaneous. Because the process of measuring the force needs a short time so try to apply force to the load cell for at least 1 second.

Place the load cell on a flat surface. Then apply a force to it with your hand. You can see when you apply more force to load the cell, a larger number is displayed on the LCD.

Code

/*
*  Digital Force Gauge with Loa d Cell
*  by Hanie kiani
*  https://electropeak.com/learn/
*/

#include "HX711.h"  //You must have this library in your arduino library folder
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 10, 9, 8, 7);
#define DOUT  4
#define CLK  5
HX711 scale(DOUT, CLK);
 
float calibration_factor = 1; // this calibration factor is adjusted according to my load cell
float units;
 
void setup() {
  lcd.begin(16,2);
  Serial.begin(9600);  
  Serial.println("Press T to tare");
scale.set_scale(calibration_factor); //Adjust to this calibration factor
  scale.tare(); 
}
 

void loop() {
  
 units = scale.get_units(), 5;
  if (units < 0)
  {
    units = 0.00;
  }
  lcd.setCursor(0,0);
  lcd.print("Force: ");
   Serial.print("Force: ");
  lcd.setCursor(8,0);
  lcd.print(units,5); //displays the weight in 4 decimal places only for calibration
   Serial.print(units,5);
  lcd.setCursor(14,0);
  lcd.print("N");
   Serial.print("N ");
     Serial.println();
delay(2000);
   
   
  if(Serial.available())
  {
    char temp = Serial.read();
    if(temp == 't' || temp == 'T')
      scale.tare();  //Reset the scale to zero      
  }
}
Warning
This code is for demonstration purposes only. In real life, it is not wise to use a load cell to measure your fist power!

What's Next?

  • By adding a potentiometer and a rotary encoder to the circuit, make the user able to change the measurement unit.
  • Add the possibility to define a custom “zero” condition. This is useful when there is already an object on the scale and you want to measure the weight of a new object.

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Comments (8)

  • Andreea Pantilimon Reply

    Wonderful tutorial. Thanks.
    It would be amazing if you put some source codes for AVR.
    Thank you again.

    May 25, 2019 at 12:44 pm
    • Saeed Hosseini Reply

      Thank you.
      We always try to do our best.

      May 26, 2019 at 4:49 am
  • JB STarkey Reply

    When pasting this code into the IDE, it says the ” error: no matching function for call to ‘HX711::HX711(int, int)” What do I need to alter in the code? I have installed all of the libraries.

    October 3, 2019 at 1:50 pm
    • Saeed Hosseini Reply

      Does your libraries up to date?

      October 6, 2019 at 12:38 pm
      • Amarnath Allemgari Reply

        Yes my libraries are up to date , still same error : no matching function for call HX711::HX711(int,int); . What need to be changed

        February 24, 2020 at 6:04 am
    • Aashay Nagrale Reply

      same bro… did you resolve it in any way

      May 27, 2020 at 12:51 pm
  • Allyson Reply

    Could you please elaborate on how this code would be changed to incorporate multiple load cells?
    I am currently working on making a three load cell scale which will measure the force applied onto it in Newtons. Any coding examples you can provide would be greatly appreciated!

    November 7, 2019 at 4:51 am
    • Saeed Hosseini Reply

      Hi,
      I think you should use three HX711 seperatly

      November 10, 2019 at 5:00 am

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