CHEAP DHT11 BASED TEMPERATURE AND HUMIDITY #12

This DHT11 (http://www.micro4you.com/files/sensor/DHT11.pdf) Temperature & Humidity Sensor features a temperature & humidity sensor complex with a calibrated digital signal output. By using the exclusive digital-signal-acquisition technique and temperature & humidity sensing technology, it ensures high reliability and excellent long-term stability. This sensor includes a resistive-type humidity measurement component and an NTC temperature measurement component, and connects to a high-performance 8-bit microcontroller, offering excellent quality, fast response, anti-interference ability and cost-effectiveness.

Each DHT11 element is strictly calibrated in the laboratory that is extremely accurate on humidity calibration. The calibration coefficients are stored as programs in the OTP memory, which are used by the sensor’s internal signal detecting process. The single-wire serial interface makes system integration quick and easy. Its small size, low power consumption and up-to-20 meter signal transmission making it the best choice for various applications, including those most demanding ones. The component is 4-pin single row pin package. 

DHT11 works on ONE wire protocol. For easy interfacing we are using library available here http://playground.arduino.cc/Main/DHT11Lib

Here's the circuit to use. Vcc (pin1) is connected to arudino's 5v pin , GND (pin 4) is connected to arduino's ground and pin 2 i.e. output of sensor is connected to pin 8 of arduino.