When it comes to electronic measurement systems, understanding how to connect a load cell to the HX711 load cell amplifier is essential for accurate weight measurement. Whether you’re designing a weighing scale or a force measurement device, mastering this connection will enable you to harness the full potential of load cells in your projects. In this detailed guide, we’ll take a long, informative journey through every step of connecting a load cell to an HX711 module, from understanding the components to coding and calibration.

Understanding Load Cells and HX711

Before diving into the connection process, it is important to familiarize yourself with the main components involved: load cells and the HX711 module.

What is a Load Cell?

A load cell is a transducer that converts a force into measurable electrical output. Load cells are essential in weighing applications because they translate the weight applied to them into an equivalent voltage signal. They come in various designs, including:

Bending beam load cells
Compression load cells
Tension load cells

Each type of load cell operates on different principles, but they generally provide very high accuracy and stability when measuring weight.

What is the HX711 Module?

The HX711 is a highly integrated precision 24-bit analog-to-digital converter (ADC) designed for weigh scales and industrial control applications. It can communicate with microcontrollers like Arduino through a simple serial interface. The HX711 amplifies the tiny signals produced by load cells and converts them into digital values that can be read and processed by microcontrollers.

Components Required for Connection

To connect a load cell to an HX711, you need a few key components:

A load cell (e.g., single-point load cell or S-type load cell)
HX711 analog-to-digital converter module
Microcontroller (e.g., Arduino, Raspberry Pi)
Jumper wires
Screw terminals (if not pre-attached)

Having these components ready will make the connection a lot smoother.

Wiring the Load Cell to HX711

The wiring process involves connecting the load cell to the HX711 module. Below are the steps to follow.

Identifying Load Cell Wires

Load cells typically come with four wires, each serving a specific function. It’s crucial to identify these wires correctly before proceeding. The color code can differ based on manufacturers, but the most common designations are as follows:

Wire Color	Function
Red	+ Excitation (E+)
Black	– Excitation (E-)
Green	+ Signal (S+)
White	– Signal (S-)

Make sure to refer to your load cell’s data sheet for the exact wiring color code.

Connecting the Load Cell to HX711

Once you have identified the wires, it’s time to connect them to the HX711 module:

Connect the load cell’s Red wire (E+) to the E+ terminal on the HX711.
Connect the load cell’s Black wire (E-) to the E- terminal on the HX711.
Connect the load cell’s Green wire (S+) to the A+ terminal on the HX711.
Connect the load cell’s White wire (S-) to the A- terminal on the HX711.

After connecting the load cell wires to the HX711, the connections may look something like this:

“`
Load Cell Wires HX711 Connections

Red (E+) –> E+
Black (E-) –> E-
Green (S+) –> A+
White (S-) –> A-
“`

Connecting HX711 to Microcontroller

With the load cell successfully wired to the HX711 module, the next step is to connect the HX711 to a microcontroller, such as an Arduino or Raspberry Pi.

Pin Connections

The necessary connections will typically include:

VCC: Connect to the 5V pin of the microcontroller.
GND: Connect to the GND pin of the microcontroller.
DT (Data): Connect to any digital pin on the microcontroller (e.g., pin 3).
SCK (Clock): Connect to any digital pin on the microcontroller (e.g., pin 2).

The wiring should look like this:

“`
HX711 Pin Microcontroller Pin

VCC –> 5V
GND –> GND
DT –> Digital Pin 3
SCK –> Digital Pin 2
“`

Programming the Microcontroller

Now that everything is connected correctly, the next step is to write code that will allow your microcontroller to communicate with the HX711.

Installing Libraries

Before writing the code, make sure to install the HX711 library for your microcontroller. For Arduino users, follow these steps:

Open the Arduino IDE.
Navigate to Sketch > Include Library > Manage Libraries.
In the Library Manager, search for “HX711” and install the HX711 library by Bogdan Necula.

Basic Arduino Code Example

Below is a simple code snippet to get you started with reading data from the load cell:

“`cpp

include “HX711.h”

// Define pins
const int LOADCELL_DOUT_PIN = 3;
const int LOADCELL_SCK_PIN = 2;

// Create HX711 object
HX711 scale;

void setup() {
Serial.begin(9600);
scale.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);
scale.set_scale(); // Set the scale to a known weight
scale.tare(); // Reset the scale to 0
}

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

This code initializes the HX711, tars (zeroes) the scale, and continuously reads the weight, printing it to the serial monitor.

Calibration of Load Cell

Calibrating your load cell is an essential step to ensure accurate readings. Here’s how you can calibrate your scale:

Calibration Procedure

Tare the scale: Make sure the load cell reads zero before placing any weight on it.
Add a known weight: Place a known weight on the load cell, ideally something easy to measure (like a 1 kg weight).
Record the reading: Note the value displayed in the serial monitor.
Calculate the scale factor: Use the formula:

Scale Factor = Measured Value / Known Weight

Update the code: Replace the scale.set_scale() line with scale.set_scale(Scale Factor); in your code.

Achieving Accurate Measurements

Once you’ve calibrated your load cell, you can achieve accurate and reliable weight measurements. However, there are a few best practices to keep in mind:

Minimize Noise

Electromagnetic interference or electrical noise can affect the accuracy of your measurements. Utilize twisted pairs for wiring to reduce noise and consider using shielding if necessary.

Regular Calibration

Periodic calibration ensures that your readings remain accurate over time. Factors such as temperature changes and mechanical stress may affect the load cell’s accuracy.

Conclusion

Connecting a load cell to the HX711 module opens the door to a wide range of electronic measurement applications. With the right wiring and configuration, you can achieve precise and reliable weight measurements for your projects.

In summary, remember that understanding the components and their connections is key to a successful setup. Ensuring that all connections are secure and double-checking your code for any errors will help you avoid common pitfalls. With patience, attention to detail, and regular calibration, your load cell and HX711 setup can provide you with data that is both accurate and dependable, whether for hobbyist projects or professional applications.

This comprehensive guide aims to equip you with the knowledge and skills required for effective load cell measurements. By embracing these practices, you can confidently harness the power of load cells and HX711 modules in your future projects, boosting both their functionality and efficacy.

What is a load cell and how does it work?

A load cell is a type of transducer that converts a force into an electrical signal. This electrical signal is proportional to the weight or load acting on the load cell. Typically, load cells are made using strain gauges that deform under load, changing their electrical resistance. This change in resistance is then measured and converted into a voltage signal that can be read by a microcontroller or processing unit.

Load cells are widely used in various applications, such as weighing scales, industrial weighing equipment, and other devices that measure force or weight. By integrating a load cell with electronic components like the HX711, you can accurately measure weight and monitor loads in real-time for different projects and applications.

What is the HX711 and its purpose?

The HX711 is a precision 24-bit analog-to-digital converter (ADC) designed specifically for weighing scales and industrial control applications. It features a built-in low-noise amplifier that allows it to amplify the tiny signals generated by load cells. The HX711 facilitates the conversion of these small analog signals into a digital format that microcontrollers can easily process.

By utilizing the HX711, you can achieve high precision and better accuracy in weight measurement. It simplifies the connection and integration of load cells with various microcontroller platforms like Arduino, Raspberry Pi, or ESP8266, enabling users to quickly develop weighing systems without needing extensive knowledge of electronics.

How do I connect a load cell to the HX711?

Connecting a load cell to the HX711 involves a few straightforward steps. First, identify the four wires of the load cell: typically, these are the red (VCC), black (GND), green (signal+), and white (signal-). Connect the red wire to the E+ pin of the HX711 and the black wire to the E- pin. Then, connect the green wire to the A+ pin and the white wire to the A- pin of the HX711.

Once the wiring is complete, connect the HX711 to a microcontroller. The HX711 has two main pins for data communication: the DT (data) pin and the SCK (serial clock) pin. These pins can be connected to any digital I/O pins on your microcontroller. With everything connected, you can proceed to upload appropriate firmware or code to read the weight data from the load cell through the HX711.

What coding libraries are available for using HX711 with load cells?

There are several coding libraries available for interfacing the HX711 with load cells, particularly for popular platforms like Arduino. One of the most commonly used libraries is the HX711 library by Bogdan Necula, which is widely recognized for its simplicity and ease of use. The library allows users to easily read the weight and calibrate their load cells with minimal coding effort.

Using these libraries typically involves installing them through the Arduino Library Manager and including the library in your sketch. The libraries provide a range of functions—such as setting the scale, reading measurements, and zeroing the scale—that make integrating the load cell with your projects much more manageable.

How do I calibrate my load cell using HX711?

Calibrating your load cell is crucial for achieving accurate weight readings. To calibrate, you’ll need to upload a simple sketch to your microcontroller that utilizes the HX711 library. The basic process involves reading the raw values from the load cell before and after placing a known weight on it. Take note of the readings for both the zero load and the applied weight.

Once you have these values, you can calculate the calibration factor. The formula to determine the calibration factor is: Calibration Factor = (Applied Weight Value) / (Raw Value at Applied Weight - Raw Value at Zero Load). Use this calibration factor in your program to convert raw readings into meaningful weight measurements accurately.

What common issues might I face when connecting a load cell to HX711?

One common issue encountered when connecting a load cell to the HX711 is incorrect wiring. It’s essential to ensure that each wire from the load cell is connected to its corresponding pin on the HX711 accurately. Misconnecting these wires can result in unreliable readings, which may lead to frustrations when attempting to troubleshoot the system.

Another issue may arise from power supply problems. The HX711 operates optimally with a stable supply voltage, typically ranging from 2.6V to 5.5V. If the power supply is inconsistent or too low, it can lead to inaccurate readings or unstable performance. To resolve such issues, ensure you are using a reliable power source and verify that the connections are secure.

Can I use multiple load cells with a single HX711?

Yes, you can use multiple load cells with a single HX711, but it requires a specific wiring setup. Your HX711 can read inputs from multiple load cells, but you’ll need to wire them in parallel to the inputs designated for the load cell on the HX711. Each load cell’s signal wires must be connected to the same A+ and A- terminals on the HX711.

When using multiple load cells, calibration becomes more complex as you’ll need to derive a new calibration factor for the combined weight of all load cells. Additionally, it’s essential to ensure that the load is distributed evenly across all cells to maintain accuracy in the readings. It’s advisable to conduct thorough testing after setting up the connections to ensure that the readings are consistent across the load cells.

Connecting a Load Cell to HX711: A Comprehensive Guide