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Web Server with Two Temperature Gauges

Created on: 3 August 2014

This project consists of two temperatures that are measured by the Arduino using two MCP9700 temperature sensors.

An Arduino Uno and Ethernet shield are set up as a web server that hosts a web page to display the two temperatures on two gauges. The web page is stored on a SD card that is plugged into the micro SD card socket on the Ethernet shield.

A web browser is used to display the two temperature gauges on any computer connected to the same network as the Arduino.

The video below shows the project working with the two MCP9700 temperature sensors connected to the Arduino using a breadboard.

Can't see the video? View on YouTube →

Circuit Diagram

Two MCP9700 temperature sensors are interfaced to the Arduino and Ethernet shield as shown in the schematic diagram below.

Two temperature sensors can be used to measure two individual temperatures, such as an inside temperature and outside temperature for example.

Schematic circuit digram of two MCP9700 temperature sensors connected to the Arduino and Ethernet shield.

Circuit Diagram of Two MCP9700 Temperature Sensor ICs Connected to the Arduino

Capacitors C2 and C4 are optional power supply decoupling capacitors. Capacitors C1 and C3 are optional capacitors for filtering the output voltage from the MCP9700's. Both sets of capacitors can be included in the circuit to make the analog output of the MCP9700 more stable.

Amazon.com

Amazon.co.uk

Arduino Sketch

The sketch below must be loaded to the Arduino. The sketch is a modified version of the two gauge Arduino web server tutorial which in turn is a modified version of part 15 of the Arduino Ethernet shield web server tutorial.

/*--------------------------------------------------------------
  Program:      two_temperatures

  Description:  Arduino web server web page displays two
                temperature values on two gauges.
                The web page is stored on the SD card.
                Ajax is used to update the analog values on the
                web page.
  
  Hardware:     Arduino Uno and official Arduino Ethernet
                shield. Should work with other Arduinos and
                compatible Ethernet shields.
                2Gb micro SD card formatted FAT16.
                MCP9700 temperature sensors interfaced to
                A2 & A3 analog inputs.
                
  Software:     Developed using Arduino 1.0.5 software
                Should be compatible with Arduino 1.0 +
                SD card contains web page called index.htm
  
  References:   - WebServer example by David A. Mellis and 
                  modified by Tom Igoe
                - SD card examples by David A. Mellis and
                  Tom Igoe
                - Ethernet library documentation:
                  http://arduino.cc/en/Reference/Ethernet
                - SD Card library documentation:
                  http://arduino.cc/en/Reference/SD
                - Gauge from:
                  https://github.com/Mikhus/canv-gauge

  Date:         3 August 2014
 
  Author:       W.A. Smith, http://startingelectronics.org
--------------------------------------------------------------*/

#include <SPI.h>
#include <Ethernet.h>
#include <SD.h>

// size of buffer used to capture HTTP requests
#define REQ_BUF_SZ   50

// MAC address from Ethernet shield sticker under board
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress ip(192, 168, 0, 20); // IP address, may need to change depending on network
EthernetServer server(80);  // create a server at port 80
File webFile;               // the web page file on the SD card
char HTTP_req[REQ_BUF_SZ] = {0}; // buffered HTTP request stored as null terminated string
char req_index = 0;              // index into HTTP_req buffer

void setup()
{
    // disable Ethernet chip
    pinMode(10, OUTPUT);
    digitalWrite(10, HIGH);

    Serial.begin(9600);       // for debugging
    
    // initialize SD card
    Serial.println("Initializing SD card...");
    if (!SD.begin(4)) {
        Serial.println("ERROR - SD card initialization failed!");
        return;    // init failed
    }
    Serial.println("SUCCESS - SD card initialized.");
    // check for index.htm file
    if (!SD.exists("index.htm")) {
        Serial.println("ERROR - Can't find index.htm file!");
        return;  // can't find index file
    }
    Serial.println("SUCCESS - Found index.htm file.");
    
    Ethernet.begin(mac, ip);  // initialize Ethernet device
    server.begin();           // start to listen for clients
}

void loop()
{
    EthernetClient client = server.available();  // try to get client

    if (client) {  // got client?
        boolean currentLineIsBlank = true;
        while (client.connected()) {
            if (client.available()) {   // client data available to read
                char c = client.read(); // read 1 byte (character) from client
                // buffer first part of HTTP request in HTTP_req array (string)
                // leave last element in array as 0 to null terminate string (REQ_BUF_SZ - 1)
                if (req_index < (REQ_BUF_SZ - 1)) {
                    HTTP_req[req_index] = c;          // save HTTP request character
                    req_index++;
                }
                // last line of client request is blank and ends with \n
                // respond to client only after last line received
                if (c == '\n' && currentLineIsBlank) {
                    // send a standard http response header
                    client.println("HTTP/1.1 200 OK");
                    // remainder of header follows below, depending on if
                    // web page or XML page is requested
                    // Ajax request - send XML file
                    if (StrContains(HTTP_req, "ajax_inputs")) {
                        // send rest of HTTP header
                        client.println("Content-Type: text/xml");
                        client.println("Connection: keep-alive");
                        client.println();
                        // send XML file containing input states
                        XML_response(client);
                    }
                    else {  // web page request
                        // send rest of HTTP header
                        client.println("Content-Type: text/html");
                        client.println("Connection: keep-alive");
                        client.println();
                        // send web page
                        webFile = SD.open("index.htm");        // open web page file
                        if (webFile) {
                            while(webFile.available()) {
                                client.write(webFile.read()); // send web page to client
                            }
                            webFile.close();
                        }
                    }
                    // display received HTTP request on serial port
                    Serial.print(HTTP_req);
                    // reset buffer index and all buffer elements to 0
                    req_index = 0;
                    StrClear(HTTP_req, REQ_BUF_SZ);
                    break;
                }
                // every line of text received from the client ends with \r\n
                if (c == '\n') {
                    // last character on line of received text
                    // starting new line with next character read
                    currentLineIsBlank = true;
                } 
                else if (c != '\r') {
                    // a text character was received from client
                    currentLineIsBlank = false;
                }
            } // end if (client.available())
        } // end while (client.connected())
        delay(1);      // give the web browser time to receive the data
        client.stop(); // close the connection
    } // end if (client)
}

// send the XML file containing analog value
void XML_response(EthernetClient cl)
{
    int analog_val_1 = 0;
    int analog_val_2 = 0;
    char sample;
    
    // get the sum of 10 samples from analog inputs 2 and 3
    for (sample = 0; sample < 10; sample++) {
        analog_val_1 += analogRead(2);
        delay(2);
        analog_val_2 += analogRead(3);
        delay(2);
    }
    // calculate the average of the 10 samples
    analog_val_1 /= 10;
    analog_val_2 /= 10;
    
    cl.print("<?xml version = \"1.0\" ?>");
    cl.print("<inputs>");
    // read analog pin A2
//    analog_val = analogRead(2);
    cl.print("<analog>");
    cl.print(analog_val_1);
    cl.print("</analog>");
//    analog_val = analogRead(3);
    cl.print("<analog>");
    cl.print(analog_val_2);
    cl.print("</analog>");
    cl.print("</inputs>");
}

// sets every element of str to 0 (clears array)
void StrClear(char *str, char length)
{
    for (int i = 0; i < length; i++) {
        str[i] = 0;
    }
}

// searches for the string sfind in the string str
// returns 1 if string found
// returns 0 if string not found
char StrContains(char *str, char *sfind)
{
    char found = 0;
    char index = 0;
    char len;

    len = strlen(str);
    
    if (strlen(sfind) > len) {
        return 0;
    }
    while (index < len) {
        if (str[index] == sfind[found]) {
            found++;
            if (strlen(sfind) == found) {
                return 1;
            }
        }
        else {
            found = 0;
        }
        index++;
    }

    return 0;
}

SD Card Hosted Web Page

The HTML markup below that contains JavaScript code must be copied to a file called index.htm, the file must then be copied to a micro SD card.

The micro SD card must be plugged into an Arduino Ethernet shield board that is plugged into an Arduino board such as the Arduino Uno. The Arduino must have the above sketch loaded to it.

Like the sketch above, the HTML page below is a modified version of the web page from the two gauge Arduino web server tutorial which in turn is a modified version of part 15 of the Arduino Ethernet shield web server tutorial.

<!DOCTYPE html>
<html>
    <head>
        <title>Arduino Two Temperatures</title>
        <script>
        var data_val = 0;
        var data_val2 = 0;
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        function GetArduinoInputs()
        {
            nocache = "&nocache=" + Math.random() * 1000000;
            var request = new XMLHttpRequest();
            request.onreadystatechange = function()
            {
                if (this.readyState == 4) {
                    if (this.status == 200) {
                        if (this.responseXML != null) {
                            data_val  = this.responseXML.getElementsByTagName('analog')[0].childNodes[0].nodeValue;
                            data_val2 = this.responseXML.getElementsByTagName('analog')[1].childNodes[0].nodeValue;
                            data_val  = ((data_val * 5.0 / 1024.0) - 0.5) / 0.01;
                            data_val2 = ((data_val2 * 5.0 / 1024.0) - 0.5) / 0.01;
                        }
                    }
                }
            }
            request.open("GET", "ajax_inputs" + nocache, true);
            request.send(null);
            setTimeout('GetArduinoInputs()', 200);
            
        }
    </script>
    </head>
    <body onload="GetArduinoInputs()">
        <h1>Arduino Two Temperatures</h1>
        <canvas id="an_gauge_1" data-title="Inside" data-units="Temp. &deg;C" width="500" height="500" data-major-ticks="-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150" data-type="canv-gauge" data-min-value="-40" data-max-value="150" data-highlights="-40 0 #4D89F2, 0 10 #25B8D9, 10 30 #0BB950, 30 40 #cc5, 40 150 #f33" data-onready="setInterval( function() { Gauge.Collection.get('an_gauge_1').setValue(data_val);}, 200);"></canvas>
        <canvas id="an_gauge_2" data-title="Outside" data-units="Temp. &deg;C" width="500" height="500" data-major-ticks="-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150" data-type="canv-gauge" data-min-value="-40" data-max-value="150" data-highlights="-40 0 #4D89F2, 0 10 #25B8D9, 10 30 #0BB950, 30 40 #cc5, 40 150 #f33" data-onready="setInterval( function() { Gauge.Collection.get('an_gauge_2').setValue(data_val2);}, 200);"></canvas>
    </body>
</html>




How the Project Works

  1. When you browse to the IP address that the Arduino web server is located at (set to 192.168.0.20 in the above Arduino sketch) using a web browser, the Arduino web server will serve up the web page from the SD card in the Arduino Ethernet shield.
  2. The JavaScript code in the web page, now running in the web browser, will request an XML file from the Arduino web server every 200ms.
  3. When the Arduino receives the request for the XML file, it will read the analog values from the two analog inputs that the MCP9700 ICs are connected to, insert them into an XML file which it will then send back to the browser.
  4. The Arduino gets ten analog samples from each of the analog inputs and sends the average of the ten samples to the browser. This adds some filtering to the analog values to try to prevent the needles on the gauges from twitching or flicking back and forth.
  5. After the browser has received the XML file, the JavaScript code in the web page will extract the analog values from the XML file and feed them to the gauges for display.

The JavaScript code converts the raw analog values to temperatures, e.g. using the following code for the first analog value:

data_val  = ((data_val * 5.0 / 1024.0) - 0.5) / 0.01;

Gauge Component

The gauge component is written by Mykhailo Stadnyk and can be downloaded from Mikhus at github. Also see a blog article on the gauge.

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