HX711 Load Sensor Demo Using Arduino | Digital Weight Measurement Project

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HX711 Load Cell Project using Arduino Uno – Digital Weighing Scale System

The HX711 Load Cell Project using Arduino is a high-precision digital weight measurement system designed to demonstrate how to build a DIY electronic weighing scale. This project uses a load cell sensor and the HX711 amplifier module to measure force and weight accurately in grams or kilograms.

Perfect for students, beginners, and electronics enthusiasts, this project explains the fundamentals of load cell operation, Wheatstone bridge principles, analog-to-digital conversion (ADC), and sensor calibration techniques using Arduino.

Project Overview

This Arduino-based digital weighing scale works by:

1️⃣ Detecting applied force using a load cell sensor
2️⃣ Amplifying millivolt signals using the HX711 module
3️⃣ Converting analog signals into 24-bit digital data
4️⃣ Calibrating readings using a known reference weight
5️⃣ Displaying real-time weight values via Serial Monitor or LCD

The HX711 simplifies precision weight measurement by providing built-in amplification and noise filtering, making it ideal for sensitive applications.

How the HX711 Load Cell System Works

 Load Cell Sensor

  • Converts mechanical force into small electrical signals

  • Uses the Wheatstone bridge principle

  • Produces millivolt-level output

HX711 Amplifier Module

  • 24-bit ADC for high resolution

  • Amplifies tiny load cell voltage changes

  • Communicates with Arduino using two wires:

    • DT (Data)

    • SCK (Clock)

 Arduino Processing

  • Reads raw ADC values

  • Performs tare (zero calibration)

  • Applies calibration factor

  • Outputs weight in kilograms or grams

 Key Features

✔ High-precision 24-bit analog-to-digital conversion
✔ Accurate digital weight measurement
✔ Simple 2-wire interface (DT & SCK)
✔ Easy tare and calibration process
✔ Real-time streaming weight data
✔ Compatible with Arduino Uno, Nano, Mega
✔ Low noise and high stability

 Learning Outcomes

This project helps learners understand:

  • Load cell working principle

  • Wheatstone bridge concept

  • Analog-to-digital conversion (ADC)

  • Signal amplification techniques

  • Calibration methods for sensors

  • Real-time data monitoring with Arduino

  • Noise reduction in measurement systems

 Applications

  • DIY digital weighing machine

  • Smart kitchen scale

  • Industrial weight monitoring system

  • IoT-based smart inventory tracking

  • Force measurement experiments

  • Packaging weight verification system

  • School and college electronics mini project

Advantages of Using HX711 with Arduino

The HX711 module eliminates the need for complex analog circuits and provides:

  • High measurement accuracy

  • Built-in gain adjustment

  • Excellent noise rejection

  • Stable and repeatable readings

  • Easy integration with Arduino

This makes it one of the most popular solutions for building low-cost precision digital weighing scales.

Technical Highlights

  • 24-bit ADC resolution

  • Gain options: 32, 64, 128

  • Low power consumption

  • Digital output interface

  • Supports calibration with known mass

  • Real-time serial data streaming

 Future Enhancements

  • LCD or OLED display integration

  • Bluetooth weight monitoring

  • WiFi IoT weight logging system

  • Automatic packaging system integration

  • Cloud-based inventory dashboard

  • Smart retail weighing machine

Code:
// HX711 simple sequential flow: tare -> cal <kg> -> stream (kg)
// Library: "HX711" by Bogdan Necula (Bogde)
// Wiring: DAT -> D4, SCK -> D5

#include <HX711.h>

const uint8_t PIN_DOUT = 4;   // DAT
const uint8_t PIN_SCK  = 5;   // CLK

// Tunables
const uint8_t AVG_TARE    = 10;    // samples for tare
const uint8_t AVG_CAL     = 10;    // samples for calibration
const uint8_t AVG_STREAM  = 5;     // samples per streamed reading
const unsigned long STREAM_MS = 200; // stream period (ms)

HX711 scale;

enum Stage { WAIT_TARE, WAIT_CAL, STREAMING };
Stage stage = WAIT_TARE;

unsigned long lastStream = 0;
String inLine;

void printIntro() {
  Serial.println(F("HX711 simple flow: tare -> cal <kg> -> streaming"));
  Serial.println(F("Commands:"));
  Serial.println(F("  tare          (no load)"));
  Serial.println(F("  cal <kg>      (known mass applied, e.g., cal 1.000)"));
  Serial.println(F("  reset         (restart flow)"));
  Serial.println();
  Serial.println(F("Step 1: Ensure no load, then type: tare"));
}

void setup() {
  Serial.begin(115200);
  while (!Serial) { /* wait for USB */ }

  scale.begin(PIN_DOUT, PIN_SCK);
  scale.set_gain(128);

  printIntro();
}

void handleSerial() {
  while (Serial.available()) {
    char c = (char)Serial.read();
    if (c == '\r') continue;
    if (c == '\n') {
      inLine.trim();
      inLine.toLowerCase();

      if (inLine == "reset") {
        stage = WAIT_TARE;
        Serial.println(F("Reset. Back to Step 1: type 'tare' with no load."));
      } else if (stage == WAIT_TARE) {
        if (inLine == "tare") {
          Serial.print(F("Taring (")); Serial.print(AVG_TARE); Serial.println(F(" samples)..."));
          scale.tare(AVG_TARE);
          Serial.print(F("Offset = ")); Serial.println(scale.get_offset());
          stage = WAIT_CAL;
          Serial.println(F("Step 2: Place known mass and type: cal <kg> (e.g., cal 1.000)"));
        } else if (inLine.length()) {
          Serial.println(F("Type 'tare' to continue (no load)."));
        }
      } else if (stage == WAIT_CAL) {
        if (inLine.startsWith("cal ")) {
          // Parse kg value after "cal "
          double kg = inLine.substring(4).toFloat();
          if (kg <= 0.0) {
            Serial.println(F("ERR: cal <kg> must be > 0, e.g., cal 1.000"));
          } else {
            // Robust calibration: flush a couple of conversions so the new load is latched
            (void)scale.read();  // flush #1
            (void)scale.read();  // flush #2

            // Average fresh raw readings
            long rawAvg = scale.read_average(AVG_CAL);
            long offset = scale.get_offset();
            long delta  = rawAvg - offset;

            Serial.print(F("rawAvg=")); Serial.print(rawAvg);
            Serial.print(F("  delta=")); Serial.println(delta);

            if (delta == 0) {
              Serial.println(F("ERR: no change from tare; check mass or re-tare."));
            } else {
              double counts_per_kg = (double)delta / kg;
              scale.set_scale(counts_per_kg);  // get_units() now returns kg
              Serial.print(F("Cal OK. counts_per_kg="));
              Serial.println(counts_per_kg, 1);

              // Quick verification read
              double kg_now = scale.get_units(AVG_CAL);
              Serial.print(F("verify kg=")); Serial.println(kg_now, 3);

              Serial.println(F("Streaming kg... (type 'reset' to redo)"));
              stage = STREAMING;
              lastStream = 0;
            }
          }
        } else if (inLine.length()) {
          Serial.println(F("Type 'cal <kg>' e.g., cal 1.000"));
        }
      } else {
        // STREAMING: allow 'reset'
      }

      inLine = ""; // clear buffer
    } else {
      inLine += c;
    }
  }
}

void loop() {
  handleSerial();

  if (stage == STREAMING) {
    unsigned long now = millis();
    if (now - lastStream >= STREAM_MS) {
      lastStream = now;
      double kg = scale.get_units(AVG_STREAM);   // returns kg (scale set by cal)
      long rawAvg = scale.read_average(AVG_STREAM);
      long offset = scale.get_offset();
      long delta  = rawAvg - offset;

      Serial.print(F("kg=")); Serial.print(kg, 3);
      Serial.print(F("  raw(avg)=")); Serial.print(rawAvg);
      Serial.print(F("  delta=")); Serial.println(delta);
    }
  }
}

 Applications

  • DIY digital weighing machine

  • Smart kitchen scale

  • Industrial weight monitoring system

  • IoT-based smart inventory system

  • Force measurement experiments

  • School and college electronics projects

Why Use HX711 with Arduino?

The HX711 module provides high accuracy and noise reduction, making it ideal for sensitive weight measurement tasks. It eliminates the need for complex analog circuitry and allows precise load cell readings with minimal wiring.

This project helps learners understand:

  • Load cell working principle

  • Wheatstone bridge concept

  • Analog-to-digital conversion (ADC)

  • Sensor calibration techniques

  • Real-time data monitoring using Arduino


 

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