Picture of The Super Simple Arduino Weather Web Server
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Added Heat Index & Dew Point calculations
Added Barometric Pressure Sensor

I wanted to set up a home web server that could monitor indoor and outdoor temperature, humidity levels, and even monitor for indoor freezing or flooding conditions (and other security, appliance or environmental alerts). The approach I took consists of a Arduino and a Ethernet shield, running a tiny web server sketch, and for this example, I'm using the popular DHT-11 Temperature / Humidity module. You can interface this to smoke / heat sensors, CO and other gas sensors, and a whole lot more.

For this example you will need:

Ethernet Shield (this could be done with wifi as well with some code changes)
DHT-11 Temp/Humidity Module
10k Ohm Resistor

Optional: BMP-085 Barometric Pressure Sensor

A internet router and home internet access
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Step 1: The DHT-11 Temperature / Humidity Sensor

Picture of The DHT-11 Temperature / Humidity Sensor
This little 4 pin sensor (only 3 are used) is an inexpensive and common sensor. It's easy to use and connect. Pin 1 connects to +5v, Pin 2 to an Arduino Input (we are using D2 on the Arduino), and pin 4 to Arduino Gnd. Since the Ethernet shield will stack on top of the Arduino, plug the DHT-11 into the same pins on the Ethernet shield.

The ethernet shield uses pins A0, A1, D4, and D10-D13
The DHT-11 is using D2, but can be changed.
The BMP180 uses A4 & A5.

Step 2: The Ethernet Shield

Picture of The Ethernet Shield
This shield from Arduino (the company) gives your Arduino (the board) the ability to communicate over the network, and internet. Write down the MAC address on the back, then plug the shield in, on top of your arduino, and connect a Ethernet cable to your router. 
diy_bloke11 months ago
great project, but are you sure you provided the correct library? I get the "DHT11 was not declared in this scope" error message, together with a hoist of other error messages
sspence (author)  diy_bloke11 months ago
Works ok for me. I'm using 1.0.5
diy_bloke sspence11 months ago
indeed, as i already posted, works in 1.05, had problems in 1.02, so it is the IDE, not your code that has the problem
oddly this error occurred in IDE1.02 worked fine in IDE1.05