1. Description
The setup allows periodic readings from a DHT11 temperature and humidity sensor using an Arduino Uno development board and an Ethernet shield. Sensor readings (temperature and humidity) as well as computed values (heat indexes) could be accessed via a minimalist webpage hosted on a SD card. The webpage refreshes sensor data using AJAX and XML.
Difficulty level: intermediate.
This is the second part of the Sensor Reading tutorial:
– Sensor Reading Part 1: Temperature and Humidity Sensor to Serial Monitor
– Sensor Reading Part 2: Temperature and Humidity Sensor to HTML
– Sensor Reading Part 3: Temperature and Humidity Sensor to HTML using JavaScript gauges
Related project: Remote Sensor (Temperature and Humidity) Monitoring over RF Link
2. Parts
– 1 x Arduino Uno R3;
– 1 x Arduino Ethernet shield (W5100);
– 1 x DHT11;
– 1 x micro-SD card;
– Breadboard + wires.
3. Schematics
(click to enlarge)
4. Assembly (breadboard)
(click to enlarge)
5. Code
The code implements a minimalist web server. It hosts a single web page (stored and loaded from the SD card) used to display useful data (sensor readings + computed values). The webpage data is updated using AJAX; an XML file containing the values to display is periodically sent from the Arduino to the client web browser.
index.htm – to be placed in the mini-SD card:
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<!DOCTYPE html> <html> <head> <style> body { background-color: #202020; } h2, a { color: #95A5A6; } p { color: white; } </style> <title>Temperature and Humidity Sensor to HTML (Arduino Uno)</title> <script> 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) { // extract XML data from XML file (containing sensor data - readings and computations) document.getElementById("humidity").innerHTML = this.responseXML.getElementsByTagName('value1')[0].childNodes[0].nodeValue; document.getElementById("tempC").innerHTML = this.responseXML.getElementsByTagName('value2')[0].childNodes[0].nodeValue; document.getElementById("tempF").innerHTML = this.responseXML.getElementsByTagName('value3')[0].childNodes[0].nodeValue; document.getElementById("heatIndexC").innerHTML = this.responseXML.getElementsByTagName('value4')[0].childNodes[0].nodeValue; document.getElementById("heatIndexF").innerHTML = this.responseXML.getElementsByTagName('value5')[0].childNodes[0].nodeValue; } } } } request.open("GET", "ajax_inputs" + nocache, true); request.send(null); setTimeout('GetArduinoInputs()', 1000); } </script> </head> <body onload="GetArduinoInputs()"> <h2>Temperature and Humidity Sensor to HTML (Arduino Uno)</h2> <p>Humidity [%]: <span id="humidity">...</span></p> <p>Temperature [C]: <span id="tempC">...</span></p> <p>Temperature [F]: <span id="tempF">...</span></p> <p>Heat Index [C]: <span id="heatIndexC">...</span></p> <p>Heat Index [F]: <span id="heatIndexF">...</span></p> <p><a href="www.arduinolab.net">www.arduinolab.net</a></p> </body> </html> |
htmlDHT11.ino – to be uploaded to Arduino:
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/*------------------------------------------------------------------------------ Program: htmlDHT11 Description: periodic readings from a DHT11 temperature and humidity sensor using an Arduino Uno development board and an Ethernet shield. Sensor readings (temperature and humidity) as well as computed values (heat indexes) could be accessed via a minimalist webpage hosted on a SD card. The webpage refreshes sensor data using AJAX and XML. Hardware: Arduino Uno R3, Arduino Ethernet shield (WT5100), DHT11. Should work with other Arduinos Software: Developed using Arduino 1.8.2 IDE Libraries: - Adafruit Unified Sensor Driver: https://github.com/adafruit/Adafruit_Sensor - DHT-sensor-library: https://github.com/adafruit/DHT-sensor-library - SPI, Ethernet and SD standard libraries (included with the Arduino IDE) References: - DHT11 datasheet: https://cdn-learn.adafruit.com/downloads/pdf/dht.pdf - Arduino Ethernet shield (WT5100) datasheet: http://www.mouser.com/catalog/specsheets/A000056_DATASHEET.pdf - Arduino Ethernet Shield Web Server Tutorial: https://startingelectronics.org/tutorials/arduino/ethernet-shield-web-server-tutorial/ Date: April 21, 2017 Author: G. Gainaru, https://www.arduinolab.net ------------------------------------------------------------------------------*/ #include <SPI.h> #include <Ethernet.h> #include <DHT.h> #include <SD.h> // sensor pin and type const int sensorPin = 3; const int sensorType = DHT11; DHT dht(sensorPin, sensorType); // controller MAC address - use your own values byte mac[] = {0x00, 0xAA, 0xBB, 0xCC, 0xDE, 0x02}; // Controller IP address IPAddress ip(192, 168, 2, 105); // initialize Ethernet server library EthernetServer server(80); // size of the buffer used to capture HTTP requests #define REQ_BUF_SZ 50 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() { Serial.begin(9600); while (!Serial) { ; // wait for serial port to connect. Needed for native USB port only } // initialize SD card Serial.println(F("initializing SD card...")); if (!SD.begin(4)) { Serial.println(F("SD card initialization failed")); return; } Serial.println(F("SD card initialized")); // check for index.htm file if (!SD.exists("index.htm")) { Serial.println(F("can't find index.htm file!")); return; // can't find index file } Serial.println(F("found index.htm file.")); // start the Ethernet connection and the server Ethernet.begin(mac, ip); server.begin(); Serial.print(F("server is at ")); Serial.println(Ethernet.localIP()); dht.begin(); // initialize sensor } void loop() { // listen for incoming clients EthernetClient client = server.available(); if (client) { Serial.println(F("new client")); // any http request ends with a blank line 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; } 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()) // give the web browser time to receive the data delay(1); // close the connection: client.stop(); Serial.println(F("client disconnected")); } } // send the XML file with values void XML_response(EthernetClient cl) { Serial.println("XML_response call"); boolean validValues = true; // sensor-specific readings float humidity = dht.readHumidity(); // humidity float tempC = dht.readTemperature(); // temperature (Celsius) float tempF = dht.readTemperature(true); // temperature (Fahrenheit) // check if any reads failed and exit early (to try again). if (isnan(humidity) || isnan(tempC) || isnan(tempF)) { validValues = false; } else { // sensor-specific computations float heatIndexC = dht.computeHeatIndex(tempC, humidity, false); // heat index (Celsius) float heatIndexF = dht.computeHeatIndex(tempF, humidity); // heat index (Fahrenheit) cl.print("<?xml version = \"1.0\" ?>"); cl.print("<inputs>"); cl.print("<value1>"); if (validValues) { Serial.print(F("Humidity [%]: ")); Serial.println(humidity); cl.print(humidity); } else { cl.print("invalid data"); } cl.print("</value1>"); cl.print("<value2>"); if (validValues) { Serial.print(F("Temperature [C]: ")); Serial.println(tempC); cl.print(tempC); } else { cl.print("invalid data"); } cl.print("</value2>"); cl.print("<value3>"); if (validValues) { Serial.print(F("Temperature [F]: ")); Serial.println(tempF); cl.print(tempF); } else { cl.print("invalid data"); } cl.print("</value3>"); cl.print("<value4>"); if (validValues) { Serial.print(F("Heat Index [C]: ")); Serial.println(heatIndexC); cl.print(heatIndexC); } else { cl.print("invalid data"); } cl.print("</value4>"); cl.print("<value5>"); if (validValues) { Serial.print(F("Heat Index [F]: ")); Serial.println(heatIndexF); cl.print(heatIndexF); } else { cl.print("invalid data"); } cl.print("</value5>"); 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, 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; } |
Note. ATmega328P-PU (Arduino Uno’s microcontroller) has 1KB SRAM memory for variables. htmlDHT11.ino includes several libraries that diminishes even more the available SRAM memory. Some recommended techniques to avoid SRAM memory saturation:
– store static strings (i.e. debugging messages) in flash memory. The size of this type of memory is 32KB for ATmega328P-PU; it’s purpose is to be used as program memory. This is the technique used in the htmlDHT11.ino sketch (usage of “F()” in some Serial.println statements);
– use conditional compiling;
– customize required libraries (strip-off whatever is not necessary).
6. Demo
7. Additional resources
Libraries:
– Adafruit Unified Sensor Driver:
https://github.com/adafruit/Adafruit_Sensor
– DHT-sensor-library:
https://github.com/adafruit/DHT-sensor-library
– SPI, Ethernet and SD standard libraries (included with the Arduino IDE)
References:
– DHT11 datasheet: https://cdn-learn.adafruit.com/downloads/pdf/dht.pdf
– Arduino Ethernet shield (WT5100) datasheet:
http://www.mouser.com/catalog/specsheets/A000056_DATASHEET.pdf
– Arduino Ethernet Shield Web Server Tutorial:
https://startingelectronics.org/tutorials/arduino/ethernet-shield-web-server-tutorial/