In this tutorial you will learn how to interface HX711 loadcell amplifier module with ESP8266 NodeMCU board and getting output on i2c OLED display. Also, we will learn how to add zero push button function to adjust scale offset.

Loadcell:

Load cell is a sensor which converts mechanical force into electronic signal. Where the mechanical force can be tension, pressure, compression or torque. There are many types of load cells are available in the market which can be used as per required application. In this example we are going to use strain gauge load cell for converting mechanical force into electrical signal.

Loadcell consist of several resistive strain gauge sensor elements which changes its resistance when the load is applied and gives output in milli volts when input or excitation voltage is applied to it.
This milli volt output is then amplified to voltage signal to make it compatible with controllers to read and convert to load units.

Things You Will Need:

• ESP8266 NodeMCU
• HX711 Amplifier Board
• 10kg Loadcell
• i2c OLED Display
• Connecting Cables

Circuit Diagram:

Code:

Example 1: ln this example we will use Arduino IDE serial monitor window to get output values from the loadcell.

/**
 *
 * Interfacing 10kg loadcell and HX711 amplifier board with ESP8266 NodeMCU
 * Author: Pranay Sawarkar
 * Website: www.eTechPath.com
 * Link: https://blog.etechpath.com/diy-weighing-scale-using-hx711-oled-i2c-display-and-esp8266-nodemcu-with-zero-calibration-function/
 * 
 *
**/

#include <Arduino.h>
#include "HX711.h"

// HX711 circuit wiring
const int Dout_Pin = 14;
const int SCK_Pin = 12;
const int pb1 = 13;            //push button input 
int tarepb = 0;
int newread = 0;
#define CalFactor 235.5    //enter your calibration factor here

HX711 scale;

void setup() {
  Serial.begin(115200);
  scale.begin(Dout_Pin, SCK_Pin);
  pinMode(pb1, INPUT_PULLUP);
  
  Serial.println("Initialization..."); 
  
  scale.set_scale(CalFactor);
  scale.tare();
  delay (200);
  Serial.println("Ready");
  delay (100);
}

void loop() {
  
  tarepb = digitalRead(pb1);
  delay(10);
  if (tarepb == LOW) 
  {
    scale.tare();
    Serial.println("TareDONE");
  }
  else
  { 
  newread = scale.get_units(5);
  Serial.println("Weight: ");
  Serial.println(newread);
  delay(10);
   }
}

Circuit Diagram:

Example 2: In this example we will interface oled display with the existing circuit and print loadcell output values on display.

/**
 *
 * DIY Weighing Scale using HX711, OLED i2c display and ESP8266 NodeMCU with Zero Calibration Function
 * Author: Pranay Sawarkar
 * Website: www.eTechPath.com
 * Link: https://blog.etechpath.com/diy-weighing-scale-using-hx711-oled-i2c-display-and-esp8266-nodemcu-with-zero-calibration-function/
 * 
 *
**/

#include <Arduino.h>
#include <U8g2lib.h>
#include "HX711.h"

#ifdef U8X8_HAVE_HW_SPI
#include <SPI.h>
#endif
#ifdef U8X8_HAVE_HW_I2C
#include <Wire.h>
#endif

//select your oled display size
U8G2_SSD1306_128X32_UNIVISION_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);
//U8G2_SSD1306_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);

// HX711 circuit wiring
const int Dout_Pin = 14;
const int SCK_Pin = 12;
const int pb1 = 13;
//const int pb2 = 5;
int tarepb = 0;
int newread = 0;
#define CalFactor 235.5

//235.5


HX711 scale;

void setup() {
  Serial.begin(115200);
  u8g2.begin();
  scale.begin(Dout_Pin, SCK_Pin);
  pinMode(pb1, INPUT_PULLUP);
  
  u8g2.clearBuffer();
  u8g2.setFont(u8g2_font_6x10_tf);
  u8g2.drawStr(0, 20, "Initializing...");
  u8g2.sendBuffer();
  
  scale.set_scale(CalFactor);
  scale.tare();
  delay (500);
  u8g2.clearBuffer();
  u8g2.drawStr(0, 20, "Ready");
  u8g2.sendBuffer();
  delay (100);
 
}

void loop() {
  
  tarepb = digitalRead(pb1);
  delay(10);
  if (tarepb == LOW) 
  {
    scale.tare();
    u8g2.clearBuffer();
    u8g2.drawStr(0, 20, "Tare Done");
    Serial.println("TareDONE");
    u8g2.sendBuffer();
  }
  else
  {
  
  newread = scale.get_units(5);
  Serial.println(newread);
  delay(10);

      u8g2.clearBuffer();
      u8g2.setFont(u8g2_font_6x10_tf);
      u8g2.drawStr(0, 20, "Weight: ");
      u8g2.setCursor(45, 20);
      u8g2.print(newread);
      u8g2.sendBuffer();
      delay(10);
    
   }
}

Prototype:

In this tutorial we will learn how to interface a MPX5010 pressure sensor with Arduino uno using onboard analog input pin A1 and generate output of sensor on serial monitor for testing then in second example we will print the sensor output on i2c OLED display using u8g2 monochrome graphics library.

MPX5010 Pressure Sensor:

• Working voltage: 4.75v – 5.25v
• Working pressure: 0 – 10 kPa
• Current: 10mA max
• Working Temperature: -40°C-125°C (0-85°C).
• Output: 0.2vdc to 4.7vdc

MPX5010 Sensor Output Calculation and Chart:

Things you will need:

• Arduino Uno or any Arduino board with a spare analog input.
• MPX5010 pressure sensor.
• SSD1306 i2c OLED display.

Circuit Diagram:

Example Code 1:

/*
 Project: Interfacing MPX5010DP with Arduino Uno.
 Project Link: 
 Website: www.etechpath.com
 Author: Pranay Sawarkar
*/

#include <Arduino.h>


void setup() {
  // initialize serial communication at 9600 bps
  Serial.begin(9600);
}

void loop() {
  // read the sensor input on analog pin 1
  int sensorValue = analogRead(A1);
  // Convert the analog reading of A1 from 0-1023 to a voltage 0-5V
  float voltage = sensorValue * (5.0 / 1023.0);
  float outputkPa = fmap(voltage, 0.2, 4.7, 0, 10);
  float outputmmH2O = fmap(voltage, 0.2, 4.7, 0, 1019.78);
  // print out the values on serial monitor
  Serial.print("Volt: ");
  Serial.println(voltage);
  Serial.print("kPa: ");
  Serial.println(outputkPa);
  Serial.print("mmH2O: ");
  Serial.println(outputmmH2O);
  Serial.println();
  delay(200);
}

float fmap(float x, float in_min, float in_max, float out_min, float out_max)
{
  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}

Example Code 1 Output:

Installing Required Library:

• Goto Sketch -> Include Library -> Manage Libraries (or Shortcut Cntl+Shift+I)
• Search u8g2 in search bar
• Select library U8g2 by Oliver
• Select latest version from dropdown menu and install. (For this project we are using version 2.31.2)

Example Code 2:

/*
 Project: Interfacing MPX5010DP with Arduino Uno and OLED i2c display.
 Project Link: 
 Website: www.etechpath.com
 Author: Pranay Sawarkar
*/

#include <Arduino.h>
#include <U8g2lib.h>

#ifdef U8X8_HAVE_HW_SPI
#include <SPI.h>
#endif
#ifdef U8X8_HAVE_HW_I2C
#include <Wire.h>
#endif

//select your oled display size
//U8G2_SSD1306_128X32_UNIVISION_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);
U8G2_SSD1306_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);

void setup() {
  // initialize serial communication at 9600 bits per second
  Serial.begin(9600);
  u8g2.begin();
}

void loop() {
  // read the sensor input on analog pin 1
  u8g2.clearBuffer();
  int sensorValue = analogRead(A1);
  // Convert the analog reading of A1 from 0-1023 to a voltage 0-5V
  float voltage = sensorValue * (5.0 / 1023.0);
  float outputkPa = fmap(voltage, 0.2, 4.7, 0, 10);
  //float outputmmH2O = fmap(voltage, 0.2, 4.7, 0, 1019.78);
  delay(50);
  u8g2.setFont(u8g2_font_6x10_tf);
  u8g2.drawStr(0, 10, "volt:");
  u8g2.setCursor(35, 10);
  u8g2.print(voltage);
  Serial.print("Volt: ");
  Serial.println(voltage);
  u8g2.drawStr(0, 22, "kPa:");
  u8g2.setCursor(35, 22);
  u8g2.print(outputkPa);
  Serial.print("kPa: ");
  Serial.println(outputkPa);
  u8g2.sendBuffer();
  delay(50);
  
}

float fmap(float x, float in_min, float in_max, float out_min, float out_max)
{
  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}

Example Code 2 Output: