Introduction

A load cell is a device used to measure force or weight. It works by converting mechanical force into electrical signals that can be measured and processed by a microcontroller like Arduino. Load cells are widely used in various applications such as digital scales, industrial weighing systems, and force measurement tools.

In this tutorial, we will learn how to interface a load cell with an Arduino board using the HX711 load cell amplifier, which allows us to read the weight or force applied to the load cell.

Required Components

To complete this tutorial, you will need the following components:

1. Arduino board (e.g., Arduino Uno, Nano, etc.)
2. Load Cell (e.g., 5kg, 10kg, or any suitable capacity)
3. HX711 Load Cell Amplifier
4. Jumper wires (for making connections)
5. Breadboard (optional, for prototyping)
6. Arduino IDE (software for writing and uploading code)
7. Power source (USB or external battery for Arduino)

Wiring Diagram & Connections

Follow the steps below to connect your load cell and HX711 to the Arduino board:

1. Connect the HX711 to the Load Cell:

   • Red wire (VCC) from the load cell to E+ on HX711.
   • Black wire (GND) from the load cell to E- on HX711.
   • White wire (S-) from the load cell to A- on HX711.
   • Green wire (S+) from the load cell to A+ on HX711.

2. Connect the HX711 to the Arduino:

   • VCC on HX711 to 5V on Arduino.
   • GND on HX711 to GND on Arduino.
   • DT (data pin) on HX711 to D2 on Arduino (or any digital pin).
   • SCK (clock pin) on HX711 to D3 on Arduino (or any digital pin).

This wiring setup is required for proper communication between the load cell, HX711, and Arduino.

Arduino Code

Here is the Arduino code for reading the weight from the load cell:

Explanation of Code:

• The HX711 library is used to interface with the load cell.
• scale.set_scale(2280.f) sets the calibration factor, which may need adjustment based on your load cell’s specifications.
• The scale.get_units() function reads the weight in grams.
• The Serial.print() function displays the measured weight on the Serial Monitor in the Arduino IDE.

Calibrating the Load Cell

Calibration ensures that the readings you get from the load cell are accurate. Here’s how you can calibrate the load cell:

1. Open the Serial Monitor in the Arduino IDE.
2. Place a known weight (e.g., 1 kg) on the load cell.
3. Adjust the scale.set_scale() value in the code (e.g., 2280.f) until the output on the Serial Monitor matches the known weight.
4. Once calibrated, remove the weight, and the output should read close to zero.
5. Note: You may need to tweak the calibration factor to get more precise readings.

Testing & Measurements

After calibration, you can begin testing the load cell by applying various known weights. The Arduino will output the weight in grams to the Serial Monitor.

Example Output:

If the output is incorrect, double-check your wiring and calibration.

Troubleshooting Common Issues

1. No output or incorrect readings:

   • Ensure that all wires are properly connected.
   • Verify that the load cell is correctly wired to the HX711 module.
   • Check the Serial Monitor baud rate matches the code’s Serial.begin(9600);.

2. Weight fluctuating:

   • If the weight fluctuates or reads “zero,” make sure the load cell is stable and not under any external forces.
   • Recalibrate using a known weight and check the scale.set_scale() value.

3. Load cell readings are very high or low:

   • Double-check the calibration factor (scale.set_scale()). Adjust it if needed.

Conclusion & Next Steps

Congratulations! You’ve successfully interfaced a load cell with an Arduino and are able to measure weight. Here are some next steps you can take:

• Integrate the system into a digital scale project.
• Build a weighing system for various applications (e.g., packaging, automation).
• Explore advanced topics like wireless data transmission of the measurements via Bluetooth or Wi-Fi.
• Learn how to add a display (e.g., an LCD screen) to show the weight readings directly on your device.