HX711 Load Cell Amplifier: Symbol, Manufacturer, Working Principle and Applications
14 November 2023
Ⅱ. HX711 symbol, footprint and pin configuration
Ⅴ. Technical parameters of HX711
Ⅵ. Working principle of HX711 pressure sensor
Ⅶ. Internal block diagram of HX711
Ⅷ. What are the applications of HX711?
The HX711 chip is specially designed for high-precision electronic scales and has a 24-bit A/D converter load sensor module. In this article, we will introduce its replacements and equivalents, pinout, features, working principle, and applications so that you can better understand this pressure sensor.
HX711 is a high-precision, low-cost pressure sensor manufactured by Avia Semiconductor in the United States, suitable for measuring changes in gravity or pressure. The sensor works normally within the power supply range of 2.6V to 5.5V and supports various sensor types such as bridges and strain gauges. The HX711 provides a simple digital interface to read analog output signals, making it ideal for embedded systems and sensor applications. It adopts dual differential input and high impedance differential input structure, which can realize single power supply. At the same time, it has built-in preamplifier, 24-bit A/D converter and digital filter. These functions enable the HX711 to achieve low cost while also ensuring measurement accuracy and reliability.
Replacements and equivalents:
• ADS1234
• HX712
• INA125P
• MCP3424
HX711 has a total of 16 pins, and their pin names and descriptions are as follows.
Pin 1 (VSUP): It is the regulated power supply pin whose range lies in between 2.7 V to 5.5 V.
Pin 2 (BASE): It is the regulator control output.
Pin 3 (AVDD): The power analog supply is applied at this pin and its value should lie in between 2.6 V and 5.5V.
Pin 4 (VFB): It is the analog control input of a regulator which is connected to analogue ground when not used.
Pin 5 (AGND): Analog ground
Pin 6 (VBG): Reference bypass output
Pin 7 (INA-): Channel A negative input
Pin 8 (INA+): Channel A positive input
Pin 9 (INB-): Channel B negative input
Pin 10 (INB+): Channel B positive input
Pin 11 (PD_SCK): Power down control (high active) and serial clock input
Pin 12 (DOUT): Serial data output
Pin 13 (XO): Digital crystal I/O
Pin 14 (XI): Digital crystal I/O or external clock input
Pin 15 (RATE): Digital input pin. It controls data rate at output. When this pin is low, data rate is 10Hz. When it is high, data rate is 80Hz.
Pin 16 (DVDD): It is the digital power supply whose value lies between 2.6V to 5.5V.
HX711 is an integrated circuit chip manufactured by Avia Semiconductor. The company is a professional integrated circuit chip design, development and sales company founded by overseas students, specializing in the design and development of analog and radio frequency integrated circuits. The chip products they have successfully developed and brought to the market include (24-bit) analog-to-digital and digital-to-analog converters, as well as BlueTooth radio frequency receiving and transmitting chips, IEEE802.11a/b/g wireless parts Internet radio frequency chip and fully integrated digital TV tuner chip. These products are Avia Semiconductor's outstanding achievements in the fields of analog and radio frequency integrated circuits.
• All controls are input through pins, and the on-chip registers do not require programming. Users have the option to select an output data rate of either 10Hz or 80Hz. Additionally, the chip features a synchronization function, effectively mitigating power interference at 50Hz and 60Hz.
• On-chip voltage stabilization circuit provides power directly to external sensors and on-chip A/D converters.
• The on-chip clock oscillator does not require any external devices, and an external crystal oscillator or clock can be used if necessary.
HX711 is based on Sigma-Delta analog-to-digital conversion technology. It achieves high-precision analog-to-digital conversion by quickly sampling the output signal of the sensor and averaging it, combined with a digital filtering algorithm. Its working principle is as follows.
1. Input signal collection
HX711 receives the sensor's output signal through four input pins (A+, A-, B+, B-). The analog output signal of the sensor is usually a small voltage change. By connecting the sensor's bridge or strain gauge to the HX711, these small voltage differences are converted into voltage signals and input to the differential input channels (A+, A-) of the HX711.
2. Analog-to-digital conversion
HX711 internally uses a 24-bit Sigma-Delta ADC to perform analog-to-digital conversion of the input signal. The core principle of the Sigma-Delta ADC is to add the input signal to high-frequency noise and then sample it. Next, it integrates, accumulates and modulates the sampling results to finally obtain a high-precision digital output.
3. Gain and offset calibration
In order to adapt to different sensors and application scenarios, HX711 provides multiple gain bits and offset calibration bits. By setting these bits, we can adjust the gain and offset of the HX711 to adapt it to sensor outputs of different ranges and accuracies. Calibration operations are usually performed during initialization and can be achieved by loading corresponding calibration parameters.
4. Digital output
The HX711's digital outputs typically use a serial interface (such as SPI or bit-banging) to transmit data. The output data is obtained by reading its internal data register, usually 24-bit two's complement. For positive values, the highest bit of the data is 0, and the remaining bits represent the actual value of the sensor. For negative values, the highest bit of the data is 1, and the remaining bits represent the sensor's complement value.
HX711 has two input circuits, A and B, and is equipped with a MUX circuit. This circuit can select only A or B channel for conversion at the same time. The data then enters the differential circuit and is converted by a 24bit ADC conversion circuit. The converted data is transmitted to the MCU via the DOUT and PD_SCK pins. At the same time, its internal voltage stabilizing circuit provides stable operating voltage for each module circuit inside the chip.
• Automation system: In some systems that require automated control, HX711 can be used to monitor and control the weight of objects to achieve automated process control.
• Internet of Things: HX711 can be used as sensor nodes in the Internet of Things, such as environmental monitoring, smart agriculture and other fields. In these fields, we need to measure physical quantities in the environment with high precision, such as temperature, humidity, pressure, etc., and transmit the data to the cloud for analysis and processing.
• Embedded systems: The small size and digital output of HX711 make it suitable for embedded systems. It can be easily connected with a microcontroller to achieve real-time monitoring and precise control of weighing.
• Smart home: It can also be used as a weight sensor in smart homes, such as smart refrigerators, smart shopping carts and other devices. These devices need to measure the weight of items with high accuracy and need to transmit the data to the main controller for analysis and processing. The high accuracy and low power consumption of the HX711 render it a perfect selection for this particular application.
Frequently Asked Questions
1. What is the working principle of HX711 amplifier?
HX711 is an electronic scale module, whose working principle is to convert the measured changes in resistance value changes, through the conversion circuit into electrical output. The module communicates with the host computer through TTL RS232.
2. What is the HX711 used for?
The HX711 amplifier is a breakout board that allows you to easily read load cells to measure weight. You wire the load cell wires on one side, and the microcontroller on the other side. The HX711 communicates with the microcontroller using two-wire interface (Clock and Data).
3. What is HX711 as normal ADC?
The HX711 is a precision 24-bit analog- to-digital converter (ADC) designed for weigh scales and industrial control applications to interface directly with a bridge sensor. It has ADC, oscillator, bandgap reference and power supply regulator integrated into the single chip.
4. How is the HX711 connected to a microcontroller?
The HX711 communicates with a microcontroller using a two-wire interface (clock and data lines). It follows a standard protocol similar to SPI (Serial Peripheral Interface).
5. How accurate is the HX711 load cell?
Going over the maximum limit can permanently damage the load cells. If you combine four cells to a single scale, then you can measures up to 4 x 50 = 200 kg / 440 lbs. Accuracy, according to the spec, is ±0.05% from the maximum rated value.
