Load Cell Amplifier 24-Bit ADC Weighing Sensor Module HX711

The Load Cell Amplifier and ADC (Analog-to-Digital Converter) Module is a small breakout board for the HX711 IC that allows you to easily read load cells to measure weight. By connecting the module to your microcontroller you will be able to read the changes in the resistance of the load cell and with some calibration you’ll be able to get very accurate weight measurements. This can be handy for creating your own industrial scale, process control, or simple presence detection.

The HX711 uses a two wire interface (Clock and Data) for communication. Any microcontroller’s GPIO pins should work and numerous libraries have been written making it easy to read data from the HX711. The module communicates with the host computer through TTL 232.

Application:
Widely used in aerospace, mechanical, electrical, chemical, construction, medicine and many other fields, used to measure force, pressure, displacement, strain, torque, acceleration.

Features:

• Two selectable differential input channels
• On-chip active low noise PGA with selectable gain of 32, 64 and 128
• On-chip power supply regulator for load-cell and ADC analog power supply
• On-chip oscillator requiring no external component with optional external crystal
• On-chip power-on-reset
• Simple digital control and serial interface: pin-driven controls, no programming needed
• Measurement Resolution: 24 bit
• Selectable 10SPS or 80SPS output data rate
• Simultaneous 50 and 60Hz supply rejection

Specification

• Differential input voltage : ±40mV ( Full-scale differential input voltage is ± 40mV )
• Data accuracy : 24 bit ( A/D converter chip )
• Refresh frequency: 80 Hz
• Operating Voltage : 5V DC (2.6V ~ 5.5V)
• Operating current : <10 mA
• Operation supply voltage range: 2.7V ~ 5.5V
• Operation temperature range: -40 ~ +85℃
• Size : 33mm x 20mm

Documents and Downloads

• HX711 Datasheet
• HX711 and Load Sensor Hookup Guide
• HX711 Arduino Library
• HX711 Example Source Codes for Arduino

Package Includes

• 1x Load Cell Amplifier and 24-Bit ADC Module based on HX711 chip
• 10 pin (6+4) Male to Male Header pins in 0.1 inch pitch

Pinouts

Analog Side

• E+  : Excitation positive
• E-  : Excitation negative
• A-  : Channel A Negative Input
• A+  :  Channel A positive Input
• B-  :  Channel B Negative Input
• B+  : Channel B positive Input

Digital Side

• GND: 0V / Ground Power Connection
• DT: Data IO Connection
• SCK: Serial Clock Input
• VCC: Power Input

Connect Load Cell Amplifier & Load Cell to Arduino

Load Cell like 500g, 20kg or even 200kg

Most strain gauge will not come with a platform. You will need to build one.
A basic scale will look something as below. Wood, plastic or metal flatsheet should do the job.

* Please download the HX711 Arduino Library

Arduino Sketch:

#include "HX711.h"
HX711 scale(A1, A0); // DOUT, SCK

void setup()
{
  Serial.begin(9600);
  scale.set_scale(2280.f); // this value is obtained by calibrating the scale with known weights
  scale.tare();
}

void loop()
{
  Serial.print("one reading:\t");
  Serial.print(scale.get_units(), 1);
  scale.power_down(); // put the ADC in sleep mode
  delay(5000);
  scale.power_up();
}

You may notice that the value extracted off the HX711 is just a number. It is really up to you to put a unit by converting this number into something meaningful weighing unit such as grams. The easiest way to do this is a simple calibration proceedure: Place a known weight on the scale, say 1000 grams and then record the reading from the HX711. Now edit the code so that every time you read, you multiply the value with 1000 and then divide it by the reading you recorded earlier. Note that you maybe better off using a float in this operation. The result shouild be the reading in gram. This of course assumes a very linear output from the sensor and is therefore not a recommended approach for applications requiring high accuracy. There are several other ways to do this but this tutorial will not cover them as we focus on getting our weight sensor up and running.

The tare function in setup()  sets the "zero-point" of the sensor to whatever is the initial weight the Arduino detects on power up. This is useful to remove the effect of the platform and/or a container used for holding the objects to be weighed.

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