MPL3115A2 sensor readings displayed on a web page

In this example we connect an Ethernet shield to an Arduino, we then connect a MPL3115A2 sensor to this and we will display the readings on a webpage

Lets take a look at the MPL3115A2.

The MPL3115A2 is a compact, piezoresistive, absolute pressure sensor with an I2C digital interface. MPL3115A2 has a wide operating range of 20 kPa to 110 kPa, a range that covers all surface elevations on earth. The MEMS is temperature compensated utilizing an on-chip temperature sensor. The pressure and temperature data is fed into a high resolution ADC to provide fully compensated and digitized outputs for pressure in Pascals and temperature in °C.

The compensated pressure output can then be converted to altitude, utilizing the formula stated in Section 9.1.3 “Pressure/altitude” provided in meters.The internal processing in MPL3115A2 removes compensation and unit conversion load from the system MCU, simplifying system design

Parts List

Part Link
Arduino Uno UNO R3 CH340G/ATmega328P, compatible for Arduino UNO
MPL3115A2 module MPL3115A2 I2C Intelligent Temperature Pressure Altitude Sensor V2.0 for Arduino
Connecting cable Free shipping Dupont line 120pcs 20cm male to male + male to female and female to female jumper wire
Arduino Ethernet shield Ethernet Shield W5100 R3 UNO and Mega 2560

 

Schematics/Layout

Connect the Ethernet shield and the connect the sensor to the shield connector, like this.

Etehrnet shield and MPL3115A2
Etehrnet shield and MPL3115A2

 

Code

Again we use a library for the sensor, the rest are built in libraries – https://github.com/adafruit/Adafruit_MPL3115A2_Library

#include <SPI.h>
#include <Ethernet.h>
#include <Wire.h>
#include <Adafruit_MPL3115A2.h>
 
 
Adafruit_MPL3115A2 baro = Adafruit_MPL3115A2();
 
// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = {
  0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
 
IPAddress ip(192,168,1, 177);
 
// Initialize the Ethernet server library
EthernetServer server(80);
 
void setup()
{
  // Open serial communications
  Serial.begin(9600);
  Ethernet.begin(mac, ip);
  server.begin();
  Serial.print("server is at ");
  Serial.println(Ethernet.localIP());
}
 
 
void loop()
{
  if (! baro.begin()) 
  {
    Serial.println("Couldnt find sensor");
    return;
  }
  // listen for incoming clients
  EthernetClient client = server.available();
  if (client) 
  {
    Serial.println("new client");
    boolean currentLineIsBlank = true;
    while (client.connected()) 
    {
      if (client.available()) 
      {
        char c = client.read();
        Serial.write(c);
        if (c == '\n' && currentLineIsBlank) 
        {
          // send a standard http response header
          client.println("HTTP/1.1 200 OK");
          client.println("Content-Type: text/html");
          client.println("Connnection: close");
          client.println();
          client.println("<!DOCTYPE HTML>");
          client.println("<html>");
          client.println("<meta http-equiv=\"refresh\" content=\"5\">");
          client.println("<br />");     
 
          float pascals = baro.getPressure();
          client.print("pressure (Inches (Hg)): ");
          client.println((float)pascals/3377, 1);  
          client.println("<br />");   
          client.print("Temperature (C): ");
          client.println((float)baro.getTemperature(), 1);  
          client.println("<br />");          
          client.print("Altitude (m): ");
          client.println((float)baro.getAltitude(), 1);  
          client.println("<br />");   
 
          client.println("</html>");
          break;
        }
        if (c == '\n') 
        {
          currentLineIsBlank = true;
        } 
        else if (c != '\r') 
        {
          currentLineIsBlank = false;
        }
      }
    }
    // give the web browser time to receive the data
    delay(1);
    // close the connection:
    client.stop();
    Serial.println("client disonnected");
  }
}

 

Output

Open your favourite web browser and type in the IP address, you should see something like this

pressure (Inches (Hg)): 29.7
Temperature (C): 19.1
Altitude (m): 84.1

 

Links

https://www.nxp.com/docs/en/data-sheet/MPL3115A2.pdf