Introduction to the Hx711 Datasheet

The Hx711 is a precision 24-bit analog-to-digital converter (ADC) designed for weigh scales and industrial control applications. It is a popular choice for interfacing load cells and strain gauges to microcontrollers like Arduino, due to its high accuracy, stability, and ease of use. The Hx711 datasheet provides detailed information about the chip’s pinout configuration, electrical characteristics, and application examples.

In this article, we will explore the Hx711 datasheet in depth, covering its pinout configuration, key features, and how to use it in your projects. We will also provide some practical examples and answer frequently asked questions about the Hx711.

Hx711 Pinout Configuration

The Hx711 comes in a small SOIC-16 package with 16 pins. The following table shows the Hx711 pinout configuration:

The most important pins for interfacing the Hx711 with a microcontroller are:
– DVDD and AVDD: Supply voltage pins, typically connected to 3.3V or 5V.
– VSS and AGND: Ground pins, connected to the system ground.
– SCK: Serial clock input, controlled by the microcontroller to read data from the Hx711.
– DT: Data output pin, goes low when data is ready to be read.

The analog input pins (INA+, INA-, VFB, BASE) are used to connect the load cell or strain gauge to the Hx711. The exact wiring depends on the type of load cell and the desired gain.

Key Features of the Hx711

The Hx711 offers several key features that make it an attractive choice for weigh scale and industrial control applications:

High Precision 24-Bit ADC

The Hx711 incorporates a 24-bit ADC with a maximum input range of ±40mV, providing high resolution and accuracy for measuring small changes in load cell output. The chip’s noise level is typically less than 50nV (RMS, at 10SPS), ensuring stable and reliable readings.

Programmable Gain Amplifier (PGA)

The Hx711 features a programmable gain amplifier (PGA) that can be set to 32, 64, or 128, allowing you to adjust the sensitivity and range of the load cell. The higher the gain, the smaller the input range, but the higher the resolution. The default gain is 128, which provides the highest resolution but the smallest input range (±20mV).

On-Chip Oscillator and Power-On Reset

The Hx711 has an on-chip oscillator that eliminates the need for an external clock source. It also includes a power-on reset circuit that ensures the chip starts up in a known state when power is applied.

Low Power Consumption

The Hx711 has a low power consumption of typically 1.5mA at 5V, making it suitable for battery-powered applications. The chip also has a power-down mode that reduces the current consumption to less than 1µA.

Simple Digital Interface

The Hx711 communicates with the microcontroller using a simple two-wire digital interface consisting of a clock line (SCK) and a data line (DT). The microcontroller initiates a conversion by sending 25 to 27 clock pulses to the Hx711, and then reads the 24-bit result on the falling edges of the next 24 clock pulses.

Using the Hx711 with Arduino

One of the most popular ways to use the Hx711 is with an Arduino board. Here’s a step-by-step guide on how to connect and use the Hx711 with Arduino:

Step 1: Wiring the Hx711 to Arduino

Connect the Hx711 to the Arduino as follows:
– DVDD and AVDD to Arduino 5V
– VSS and AGND to Arduino GND
– SCK to Arduino digital pin 2
– DT to Arduino digital pin 3
– INA+ and INA- to the load cell positive and negative output wires
– VFB to the load cell shield (if present) or to AGND

Step 2: Installing the Hx711 Arduino Library

To simplify the communication between the Arduino and the Hx711, you can use the Hx711 Arduino library. Install the library through the Arduino IDE Library Manager or download it from GitHub and install it manually.

Step 3: Calibrating the Load Cell

Before using the load cell with the Hx711, you need to calibrate it to obtain accurate weight measurements. The calibration process involves measuring the Hx711 output with no load and with a known load, and then calculating a calibration factor.

Here’s an example calibration sketch:

#include "HX711.h"

HX711 scale;

float calibration_factor = -7050; // Change this value to match your load cell

void setup() {
  Serial.begin(9600);
  scale.begin(2, 3);
  scale.set_scale(calibration_factor);
  scale.tare(); // Reset the scale to 0
}

void loop() {
  Serial.print("Reading: ");
  Serial.print(scale.get_units(), 1);
  Serial.print(" lbs");
  Serial.println();
}

To calibrate the load cell:
1. Upload the sketch to the Arduino.
2. Place a known weight on the load cell.
3. Adjust the calibration_factor value until the Arduino output matches the known weight.

Step 4: Measuring Weight

Once the load cell is calibrated, you can use the Hx711 to measure weight. Here’s an example sketch:

#include "HX711.h"

HX711 scale;

float calibration_factor = -7050; // Change this value to match your load cell

void setup() {
  Serial.begin(9600);
  scale.begin(2, 3);
  scale.set_scale(calibration_factor);
  scale.tare(); // Reset the scale to 0
}

void loop() {
  Serial.print("Weight: ");
  Serial.print(scale.get_units(), 2);
  Serial.println(" lbs");
  delay(500);
}

This sketch will continuously read the weight from the load cell and print it to the Arduino Serial Monitor.

Hx711 Application Examples

The Hx711 can be used in a wide range of weigh scale and industrial control applications. Here are a few examples:

Digital Kitchen Scale

A digital kitchen scale can be built using the Hx711, a load cell, and an Arduino or other microcontroller. The load cell measures the weight of the items placed on the scale, and the Hx711 converts the analog signal to a digital value that can be displayed on an LCD or OLED screen.

Outdoor Weather Station

The Hx711 can be used in an outdoor weather station to measure wind speed and direction using a strain gauge-based anemometer. The strain gauges measure the force exerted by the wind on the anemometer arms, and the Hx711 converts the analog signal to a digital value that can be used to calculate wind speed and direction.

Industrial Process Control

The Hx711 can be used in industrial process control applications to measure the weight or force of materials during manufacturing or packaging. For example, a load cell can be used to measure the weight of a product on a conveyor belt, and the Hx711 can provide feedback to the control system to ensure that the correct amount of product is being packaged.

Frequently Asked Questions (FAQ)

1. What is the maximum input range of the Hx711?

The Hx711 has a maximum input range of ±40mV, but the actual input range depends on the selected gain. With a gain of 128 (the default), the input range is ±20mV.

2. How do I change the gain on the Hx711?

To change the gain on the Hx711, you need to send a series of clock pulses to the chip while the PD_SCK pin is high. The number of pulses determines the gain:
– 25 pulses: gain = 128
– 26 pulses: gain = 64
– 27 pulses: gain = 32

3. Can I use multiple Hx711 chips with one microcontroller?

Yes, you can use multiple Hx711 chips with one microcontroller by connecting each chip’s SCK and DT pins to separate digital pins on the microcontroller. You will need to create a separate instance of the Hx711 library for each chip.

4. How do I calibrate my load cell with the Hx711?

To calibrate your load cell with the Hx711, you need to measure the Hx711 output with no load and with a known load, and then calculate a calibration factor. See the “Calibrating the Load Cell” section in this article for a detailed example.

5. What is the output data rate of the Hx711?

The Hx711 has a selectable output data rate of 10SPS or 80SPS (samples per second). The data rate is controlled by the RATE pin: when RATE is high (the default), the data rate is 10SPS; when RATE is low, the data rate is 80SPS. The higher data rate provides faster measurements but may be more susceptible to noise.

Conclusion

The Hx711 is a versatile and highly accurate ADC that is well-suited for weigh scale and industrial control applications. Its high precision 24-bit ADC, programmable gain amplifier, and simple digital interface make it easy to use with microcontrollers like Arduino.

In this article, we explored the Hx711 datasheet in depth, covering its pinout configuration, key features, and how to use it with Arduino. We also provided some practical application examples and answered frequently asked questions about the Hx711.

By understanding the Hx711 datasheet and its capabilities, you can effectively use this powerful chip in your own projects to measure weight, force, and other analog signals with high accuracy and reliability.