Arduino Digital Weight Scale with HX711 & Load Cell

1. Introduction

The ability to measure weight accurately is crucial in many applications, from industrial settings to home projects. With Arduino and the HX711 load cell module, you can build a digital weight scale that is both cost-effective and highly precise.

1.1 Overview of Digital Weight Measurement Systems

Traditional weighing scales use mechanical or analog methods, whereas digital weight measurement utilizes electronic load cells to measure force and convert it into an electrical signal.

1.2 Importance of Precision in Weight Measurement

Precision is critical for applications such as food measurement, industrial weighing systems, and laboratory experiments. Using the HX711 load cell module allows for high-resolution measurements, making it a preferred choice among makers and professionals.

For a deep dive into how digital weighing scales work, check out this technical guide.

1.3 Introduction to Arduino-Based Weight Measurement

With Arduino, building a custom weight measurement system becomes simple. The HX711 amplifier module ensures the raw data from the load cell is accurately processed and displayed.

To understand the HX711 module in detail, refer to this technical document.

2. Understanding Load Cells

2.1 What is a Load Cell?

A load cell is a transducer that converts force or weight into an electrical signal. It consists of strain gauges that detect deformation when weight is applied.

2.2 Types of Load Cells

Strain Gauge Load Cells – Most common, uses electrical resistance changes.
Pneumatic Load Cells – Uses air pressure.
Hydraulic Load Cells – Uses liquid pressure.

2.3 Applications of Load Cells

Load cells are used in:

Retail scales (grocery stores, jewelry scales)
Industrial applications (bulk material weighing)
Medical scales (patient weight monitoring)

3. Introduction to the HX711 Load Cell Amplifier Module

3.1 Overview of the HX711 Module

The HX711 is a 24-bit analog-to-digital converter (ADC) designed for precision weight measurement.

3.2 Features and Specifications

Two differential input channels
Adjustable gain (32, 64, or 128)
Low-noise, high-accuracy measurement

3.3 Advantages of Using HX711 with Load Cells

High precision and resolution
Easily interfaces with Arduino
No need for an external ADC

4. Components Required for Building a Digital Weight Scale

4.1 Arduino Board Selection

Arduino Uno (Recommended for beginners)
Arduino Nano (Compact alternative)

4.2 Load Cell Selection

Choose based on:

Weight capacity (e.g., 5kg, 10kg, 50kg)
Shape (bar, S-type, shear beam)

4.3 HX711 Module

Used to amplify and digitize load cell signals.

4.4 Additional Components

LCD Display (16×2 or OLED)
Resistors and Jumpers
Power Supply (5V)

5. Setting Up the Load Cell and HX711 Module

5.1 Mechanical Assembly of the Load Cell

Ensure the load cell is mounted on a flat, stable surface.
Attach a known weight for calibration.

5.2 Wiring the Load Cell to the HX711 Module

Load Cell Wires	HX711 Pins
Red (E+)	E+
Black (E-)	E-
White (A-)	A-
Green (A+)	A+

5.3 Connecting the HX711 Module to the Arduino

HX711 Pins	Arduino Pins
VCC	5V
GND	GND
DT	Digital Pin 3
SCK	Digital Pin 2

Arduino Digital Weight Scale HX711 Load Cell Module

6. Programming the Arduino for Weight Measurement

6.1 Installing Necessary Libraries

#include "HX711.h"
HX711 scale(3, 2);  // DT, SCK

6.2 Writing the Calibration Code

scale.set_scale();  // Adjust this after calibration
scale.tare();  // Reset scale to zero

6.3 Implementing the Weight Measurement Code

void loop() {
    Serial.print("Weight: ");
    Serial.println(scale.get_units(), 2);
    delay(500);
}

#include <HX711_ADC.h> // https://github.com/olkal/HX711_ADC
#include <Wire.h>
#include <LiquidCrystal_I2C.h> // LiquidCrystal_I2C library
HX711_ADC LoadCell(4, 5); // dt pin, sck pin
LiquidCrystal_I2C lcd(0x27, 16, 2); // LCD HEX address 0x27
int taree = 6;
int a = 0;
float b = 0;

void setup() {
  pinMode (taree, INPUT_PULLUP);
  LoadCell.begin(); // start connection to HX711
  LoadCell.start(1000); // load cells gets 1000ms of time to stabilize

  /////////////////////////////////////
  LoadCell.setCalFactor(375); // Calibarate your LOAD CELL with 100g weight, and change the value according to readings
  /////////////////////////////////////
  
  lcd.begin(); // begins connection to the LCD module
  lcd.backlight(); // turns on the backlight
  lcd.setCursor(1, 0); // set cursor to first row
  lcd.print("Digital Scale "); // print out to LCD
  lcd.setCursor(0, 1); // set cursor to first row
  lcd.print(" 5KG MAX LOAD "); // print out to LCD
delay(3000);
lcd.clear();
}
void loop() { 
  lcd.setCursor(1, 0); // set cursor to first row
  lcd.print("Digital Scale "); // print out to LCD 
  LoadCell.update(); // retrieves data from the load cell
  float i = LoadCell.getData(); // get output value
 if (i<0)
 {
  i = i * (-1);
  lcd.setCursor(0, 1);
  lcd.print("-");
   lcd.setCursor(8, 1);
  lcd.print("-");
 }
 else
 {
   lcd.setCursor(0, 1);
  lcd.print(" ");
   lcd.setCursor(8, 1);
  lcd.print(" ");
 }
  
  lcd.setCursor(1, 1); // set cursor to secon row
  lcd.print(i, 1); // print out the retrieved value to the second row
  lcd.print("g ");
  float z = i/28.3495;
  lcd.setCursor(9, 1);
  lcd.print(z, 2);
  lcd.print("oz ");

  if (i>=5000)
  {
    i=0;
  lcd.setCursor(0, 0); // set cursor to secon row
  lcd.print("  Over Loaded   "); 
  delay(200);
  }
  if (digitalRead (taree) == LOW)
  {
    lcd.setCursor(0, 1); // set cursor to secon row
    lcd.print("   Taring...    ");
    LoadCell.start(1000);
    lcd.setCursor(0, 1);
    lcd.print("                ");
  }
}

6.4 Displaying Weight Readings on LCD

Modify the loop to display readings on an LCD/OLED screen.

7. Calibrating the Digital Weight Scale

7.1 Importance of Calibration

Calibration ensures accurate weight measurements by setting a scaling factor.

7.2 Step-by-Step Calibration Process

Place a known weight.
Adjust the scaling factor in the code.
Re-test with different weights.

8. Testing and Troubleshooting

8.1 Initial Testing Procedures

Check wiring.
Ensure Arduino is receiving data from HX711.

8.2 Common Issues and Solutions

Fluctuating readings? Use a stable power source.
No output? Verify load cell and HX711 wiring.

9. Advanced Features and Enhancements

9.1 Adding a Tare Function

scale.tare();  // Resets to zero

9.2 Data Logging Capabilities

Save readings to an SD card
Transmit data via Wi-Fi/Bluetooth

9.3 Integrating Multiple Load Cells

Combine multiple load cells for higher weight capacity.

10. Applications and Use Cases

Kitchen Scales – Precise ingredient measurement.
Health and Fitness – Smart weight tracking.
Industrial Weighing – Bulk weight management.

11. FAQs

11.1 How does a load cell work with an Arduino?

A load cell sends an analog signal to the HX711 module, which converts it to digital format for the Arduino.

11.2 How can I improve accuracy?

Use shielded cables.
Perform regular calibration.

12. Conclusion

By using an Arduino, HX711 module, and a load cell, you can build a highly accurate and reliable digital weight scale. With proper calibration and setup, this project can be used in various applications from personal use to industrial measurements.