Interface DHT22 DHT11 Temperatue Humidity Sensor AT89C51 P89V51RD1 AT89C51 AT89C52

About DHT22
(AM2302) Temperature and Humidity SensorDHT22 is very cost effective and low cost humidity and temperature sensor easily  
available in the market at very low price. This unit is combined with two components a capacitive humidity sensor and a thermistor making it a very reliable and accurate temperature and humidity measuring sensor of all time. It produces only digital value on the data pins so no analog pin needed, and data pin directly connected with  microcontroller. It is easy to install and grab the temperature value. The only drawback of this sensor is, it can produce temperature value as fast as upto 2 seconds only. It has only three pins one for 3-5 volts to provide supply voltage, another is to produce sensor value to microcontroller and the third one is the negative power supply. Be careful  its not a 1 wire based sensor. Only one sensor can be connected to same data pin. AM2302 sensor is integrated in a plastic box and formed DHT22 sensor. It works on signal collecting method and humidity sensing technology with high reliability and stability. You can interface DHT22 with AT89C51 P89V51RD1 easily.
Difference between DHT22  Vs DHT11 Temperature Humidity Sensor
The DHT22 is based on AM2302 sensor is little bit expensive than DHT11 sensor due to its speed, calibration and accuracy. Its specifications and features are very versatile and advanced. With the accuracy of +-0.5 degree it temperature measurement range is from -40 to +125 degree with high degree of accuracy. On the other hand DHT11 temperature range as comparatively is 0-50 degree with accuracy of +-2 degree. On the other hand DHT22 sensor measures humidity from 0 to 100% degree with accuracy range is 2-5% accuracy and DHT11 measures from 20-80%  with accuracy 5%. DHT22 is an advanced version of DHT11 temperature sensor module. Sensor comes with 4 pins but only three pins are used to integrate this. 
Features and Specifications of DHT22 Sensor
  • DHT22 is a very inexpensive and Low cost sensor
  • Power input is 3 to 5V power and I/O
  • Only 2.5mA max current used while conversion
  • Suitable for reading for 0-100% humidity readings with 2-5% accuracy
  • Suitable for -40 to 80°C temperature readings ±0.5°C accuracy
  • Module Body size 27mm x 59mm x 13.5mm (1.05″ x 2.32″ x 0.53″)
  • Pinout is of 4 pins, 0.1″ spacing
  • Weight is just 2.4g

Applications DHT22 (AM2302) Temperature and Humidity Sensor 
  • Measuring temperature and humidity
  • Weather Station Predictions
  • Automatic climate control systems
  • Environment and Atmospheric Monitoring Applications
  • Industrial furnaces
  • Medical equipment and devices  
How To Interface DHT22 with Microcontrollers AT89C51 P89V51RD1 AT89C51 AT89C52
Its ve
ry simple to interface DHT22 with any microcontroller, below given circuit is used to connect it to microcontroller. Its a factory calibrated sensor and data is transferred with serial method using one pin and very easy to setup the connection. The given diagram shows.
The data pin is connected to the microcontroller input output pin and a 4K pull up resistor is used in order to do so. Single pin is used for measuring humidity and temperature with serial method. If you are interfacing with 8051 microcontrollers then its little bit difficult but because you need to write down the entire code manually. On the other hand if you are using Arduino UNO then ready made libraries are available for this.
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