How to Use Arduino with Load Cell and HX711 for Weight Measurement

This guide walks you through connecting a Load Cell and HX711 amplifier module to Arduino UNO R3 for reading weight values. We’ll cover wiring, library installation, calibration, and practical usage.

Required Components

• Arduino UNO R3 with USB cable
• HX711 amplifier module with Load Cell (choose capacity: 1kg, 5kg, 10kg, 20kg, etc.)
• MB-102 Breadboard 830 Point
• Jumper wires: Male-Male, Male-Female, Female-Female, 20cm length
• Reference weight with known mass for calibration (e.g., 600ml water bottle or calibration weights)

![Layout diagram showing Arduino on top of breadboard with HX711 module and Load Cell properly positioned]

Wiring: Arduino UNO to HX711

Arduino → HX711 Connections

Arduino	HX711
5V	VCC
GND	GND
A2	SCK
A3	DT

HX711 → Load Cell Connections

HX711	Load Cell Wire
E+	Red wire
E-	Black wire
A-	White wire
A+	Green wire

![Circuit diagram showing complete wiring between Arduino, HX711 module, and Load Cell with pin labels clearly marked]

Note: Wire colors may vary by manufacturer. Refer to your Load Cell documentation if colors don’t match the table above.

Installing HX711 Library

1. Download the HX711 library from GitHub or Arduino Library Manager
2. Extract to Documents/Arduino/libraries/ folder
3. Open Arduino IDE and go to Sketch → Include Library → HX711

Calibration Process Using Serial Monitor

Why Calibration is Needed

The raw ADC value from HX711 is not actual weight. A Calibration Factor must be calculated using a known reference weight, and a Zero Offset must be set before measuring.

Step 1: Access Calibration Sketch

1. Open Arduino IDE and go to File → Examples → HX711 → Arduino_Auto_Cal
2. Modify the real_weight variable to match your reference weight in kilograms
3. Upload the sketch to your board
4. Open Serial Monitor at 9600 baud

Available Commands

Command	Function
a	Set Zero Offset (remove all objects from platform first)
b	Start Calibration (place reference weight on platform first)
c	Test calibration results

Calibration Step 1: Set Zero Offset

1. Ensure nothing is placed on the Load Cell platform
2. Type a and press Send
3. Record the zero factor value displayed

Calibration Step 2: Find Calibration Factor

1. Place your reference weight on the platform (e.g., two 600ml water bottles ≈ 1.25kg)
2. Type b and press Send
3. Wait for the calibration factor value (this takes a moment)
4. Record this value for the next step

![Serial Monitor showing calibration process with zero factor and calibration factor values displayed]

Calibration Step 3: Test Results

1. Type c and press Send
2. The displayed value should be close to your reference weight
3. Remove the object - value should return to 0.00 kg

Practical Usage After Calibration

1. Open File → Examples → HX711 → ex_loadcell
2. Enter your calibration_factor and zero_factor values
3. Upload the sketch
4. Open Serial Monitor to view weight readings

Test Results

Object	Actual Weight (approx)	Reading
600ml water bottle	0.60-0.65 kg	0.63 kg
600ml water bottles x2	1.20-1.30 kg	1.25 kg
1kg steel weight	1.00 kg	1.00 kg

Measured values have less than 5% error compared to a standard digital scale.

Common Problems and Solutions

Problem: Readings fluctuate a lot

• Use a stable base platform
• Use averaging: get_units(10) for 10 samples
• Check for loose connections

Problem: Negative or abnormal values

• Verify Load Cell wire connections - E+/E- or A+/A- may be swapped
• Re-run calibration from Step 1

Problem: Upload succeeds but no readings in Serial Monitor

• Verify correct Port and Board selection
• Check Baud Rate matches the code (9600)

Complete Working Code

After calibration, use this ready-to-use code:

#include "HX711.h"

// Pin definitions
const int LOADCELL_DOUT_PIN = A3;
const int LOADCELL_SCK_PIN = A2;

// TODO: Replace with your calibration values
const float CALIBRATION_FACTOR = -7050.00;  // Value from step b
const long ZERO_FACTOR = 8267554;           // Value from step a

HX711 scale;

void setup() {
  Serial.begin(9600);
  Serial.println("HX711 Weight Scale Ready");
  
  scale.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);
  scale.set_scale(CALIBRATION_FACTOR);
  scale.set_offset(ZERO_FACTOR);
  
  Serial.println("Place object on scale...");
}

void loop() {
  if (scale.is_ready()) {
    float weight = scale.get_units(5);
    Serial.print("Weight: ");
    Serial.print(weight, 2);
    Serial.println(" kg");
  } else {
    Serial.println("HX711 not ready");
  }
  delay(500);
}

Summary

Using Arduino with Load Cell and HX711 for weight measurement follows these steps:

1. Wire according to pin mapping: Arduino → HX711 → Load Cell
2. Install HX711 library
3. Calibrate using a known reference weight via Serial Monitor commands a, b, c
4. Enter calibration_factor and zero_factor into the main code
5. Start measuring

After calibration, readings are reasonably accurate and suitable for DIY weighing scales, liquid level monitoring in tanks, or IoT projects requiring weight measurement.

Reference Video

https://www.youtube.com/embed/ycWyJg6Q_4M