This is a quick post to show how easy it is to connect a DHT22 temp and Humidity sensor to an Arduino and have it output its reading on a web page that can easily be accessible from anywhere on the internet
With a little more work you can pretty up the display and add other features. This is just to demonstrate a proof of concept to you
The library is directly from the Arduino Playground, what I am demonstrating here is how to combine a few libraries to create something useful, a little more than a blinky sketch. I have found through experience that there is a lot of good educational material on the internet to do just a single function but not too much that actually is useful beyond the educational aspect. What I am going to do in the coming weeks is to build upon this sample prototype in this post and create a full blown useful home thermostat or something similar.
this is the sensor :-
and the ENC Card looks like this
or you can use a Wiznet based Shield
Parts are available from eBay, AdaFruit, Sparkfun and other suppliers
Please provide feedback as to any features you would like to see in this as we progress and I will try to include some.
Oh and for those not following along closely, the Arduino is acting as the web server in this case, you don't need a separate server
Thanks
Peter
Code for the proof of concept
#include <SPI.h>
#include <Wire.h>
#include <Ethernet.h>
//#include <UIPEthernet.h>
#include <dht.h>
#include <stdio.h>
dht DHT;
#define DHT22_PIN 2
float combined_temp_C;
float combined_temp_F; //create a new variable
byte TempHi; // Variable hold data high byte
byte TempLo; // Variable hold data low byte
boolean P_N; // Bit flag for Positive and Negative
boolean P_N112;
boolean P_N212;
unsigned int Decimal; // Variable hold decimal value
char * strTempC = NULL;
char * strTempF = NULL;
byte mac[] = { 0x90, 0xA2, 0xDA, 0x00, 0x4E, 0x10 }; // MAC address 84.85.88.16.0.36
byte ip[] = { 192, 168, 1, 203 }; // ip-address, please change to fit your network
byte mydns[] = { 192, 168, 1, 1 };
byte gateway[] = { 192, 168, 1, 1 };
byte subnet[] = { 255,255,255,0 };
EthernetServer server(80);
static char output[300] = "";
void setup() {
Serial.begin(9600);
//ethernet
Ethernet.begin(mac, ip);
server.begin();
Serial.print("server is at ");
Serial.println(Ethernet.localIP());
}
char headerHTML[] = "HTTP/1.1 200 OK\r\n"
"Content-Type: text/html\r\n"
"Connection: close\r\n"
"Refresh: 5\r\n"
"\r\n"
"<!DOCTYPE HTML>"
"<Title>RBBS Server</Title>"
"<html>";
char footerHTML[] = "</html>" ;
char * TimeElapsed() { // Was Home Page
long t = millis() / 1000;
word h = t / 3600;
byte m = (t / 60) % 60;
byte s = t % 60;
sprintf(output, "<h1>%d%d:%d%d:%d%d</h1>" , h/10, h%10, m/10, m%10, s/10, s%10);
return output;
}
void sendTempToNetwork(EthernetClient myClient)
{
// now humidity / temp sensor
int chk = DHT.read22(DHT22_PIN);
myClient.print("Humidity=");
myClient.print(DHT.humidity,0);
myClient.print("%");
myClient.print("<BR/>");
myClient.print("Temperature=");
myClient.print(DHT.temperature, 0);
myClient.write(" ");
myClient.print("C");
myClient.print("<BR/>");
myClient.print("Dewpoint=");
myClient.print(dewPoint(DHT.temperature,DHT.humidity), 0);
myClient.write(" ");
myClient.print("C");
myClient.print("<BR/><BR/>");
}
void sendAnalogToNetwork(EthernetClient myClient)
{
// output the value of each analog input pin for good measure
for (int analogChannel = 0; analogChannel < 6; analogChannel++) {
int sensorReading = analogRead(analogChannel);
myClient.print("analog input ");
myClient.print(analogChannel);
myClient.print(" is ");
myClient.print(sensorReading);
myClient.println("<br />");
}
}
/*******************************************************************************
* Main Loop
*******************************************************************************/
void loop()
{
// listen for incoming clients
EthernetClient client = server.available();
if (client) {
Serial.println("new client");
// an http request ends with a blank line
boolean currentLineIsBlank = true;
while (client.connected()) {
if (client.available()) {
char c = client.read();
Serial.write(c);
// if you've gotten to the end of the line (received a newline
// character) and the line is blank, the http request has ended,
// so you can send a reply
if (c == '\n' && currentLineIsBlank) {
// send a standard http response header
client.print(headerHTML);
// now send the stuff we want
client.print(TimeElapsed()); // your old code here
// do some more stuff
sendTempToNetwork(client);
sendAnalogToNetwork(client);
// were done sending so now send the footer to close the page
client.println(footerHTML);
break;
}
if (c == '\n') {
// you're starting a new line
currentLineIsBlank = true;
}
else if (c != '\r') {
// you've gotten a character on the current line
currentLineIsBlank = false;
}
}
}
// give the web browser time to receive the data
delay(1);
// close the connection:
client.stop();
Serial.println("client disconnected");
}
delay(2000);
}
void Cal_Temp()
{
if (TempHi&0x80) // If bit7 of the TempHi is HIGH then the temperature is negative
P_N = 0;
else // Else the temperature is positive
P_N = 1;
TempHi = TempHi & 0x7F; // Remove sign
TempLo = TempLo & 0xF0; // Filter out last nibble
TempLo = TempLo >>4; // Shift right 4 times
Decimal = TempLo;
Decimal = Decimal * 625; // Each bit = 0.0625 degree C
combined_temp_C= TempHi + TempLo*.0625;
combined_temp_F = combined_temp_C*1.8+32;
sprintf(strTempC, "%f", combined_temp_C);
sprintf(strTempF, "%f", combined_temp_F);
}
////Celsius to Kelvin conversion
//double Kelvin(double celsius)
//{
// return celsius + 273.15;
//}
// dewPoint function NOAA
// reference: http://wahiduddin.net/calc/density_algorithms.htm
double dewPoint(double celsius, double humidity)
{
double A0= 373.15/(273.15 + celsius);
double SUM = -7.90298 * (A0-1);
SUM += 5.02808 * log10(A0);
SUM += -1.3816e-7 * (pow(10, (11.344*(1-1/A0)))-1) ;
SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ;
SUM += log10(1013.246);
double VP = pow(10, SUM-3) * humidity;
double T = log(VP/0.61078); // temp var
return (241.88 * T) / (17.558-T);
}
// delta max = 0.6544 wrt dewPoint()
// 5x faster than dewPoint()
// reference: http://en.wikipedia.org/wiki/Dew_point
double dewPointFast(double celsius, double humidity)
{
double a = 17.271;
double b = 237.7;
double temp = (a * celsius) / (b + celsius) + log(humidity/100);
double Td = (b * temp) / (a - temp);
return Td;
}
The DHT22 Library can be found here
http://arduino.cc/playground/Main/DHTLib
This is a sample of the code and also the resulting output on a web browser to show it works
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