Build a Digital Scale Using a Load Cell

Difficulty Level: Intermediate

This project will guide you through building a digital scale using a load cell, HX711 amplifier, and an Arduino microcontroller. This system can measure weight and display it on an LCD or via a web interface (using an ESP8266).

Components Required

• Arduino Uno (or ESP8266 for web interface)
• HX711 Load Cell Amplifier Module
• Load Cell (1-5 kg capacity recommended)
• 16x2 LCD Display (optional for direct weight display)
• Jumper wires, Breadboard
• USB cable for programming

Wiring the Circuit

Follow these steps to connect the load cell, HX711 module, and Arduino:

• Load Cell to HX711:
  • Red Wire: Connect to E+ (Excitation +)
  • Black Wire: Connect to E- (Excitation -)
  • White Wire: Connect to A- (Signal -)
  • Green Wire: Connect to A+ (Signal +)
• HX711 to Arduino:
  • VCC: Connect to 5V on Arduino
  • GND: Connect to GND on Arduino
  • DT (Data): Connect to Pin 3
  • CLK (Clock): Connect to Pin 2

Arduino Code

Use the code below to measure weight using the HX711 module:

#include "HX711.h"

// Pin definitions
const int LOADCELL_DOUT_PIN = 3;
const int LOADCELL_SCK_PIN = 2;

HX711 scale;

void setup() {
    Serial.begin(9600);
    scale.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);
    Serial.println("Digital Scale ready");
    scale.set_scale(2280.f); // Adjust this calibration factor
    scale.tare(); // Set the scale to 0
}

void loop() {
    Serial.print("Weight: ");
    Serial.print(scale.get_units(10), 1); // Average of 10 readings
    Serial.println(" kg");
    delay(1000);
}
        

To calibrate your scale, replace the 2280.f value with a factor that matches your load cell. Use a known weight to determine the correct value.

Optional: Display Weight on an LCD

You can connect a 16x2 LCD display to your Arduino to show weight readings in real time:

#include <LiquidCrystal.h>
LiquidCrystal lcd(7, 8, 9, 10, 11, 12); // Configure pins

void setup() {
    lcd.begin(16, 2);
    lcd.print("Weight: ");
}

void loop() {
    float weight = scale.get_units(10); // Get weight
    lcd.setCursor(0, 1); // Move to the second row
    lcd.print(weight);
    lcd.print(" kg");
    delay(1000);
}
        

Testing and Calibration

Upload the code to your Arduino and open the Serial Monitor to see weight updates. Adjust the calibration factor for accurate measurements.

Conclusion

By completing this project, you’ve built a functional digital scale. You can expand it with IoT capabilities using an ESP8266 or add logging and remote display features.

Next Steps: Explore how to integrate wireless connectivity for remote weight monitoring or add an SD card module for data logging.