Temperature and Humidity Sensor

Temperature and humidity (DHT11) sensor

The DHT11 is a basic, ultra low-cost digital temperature and humidity sensor. It uses a capacitive humidity sensor and a thermistor to measure the surrounding temperature. There is also a very basic chip inside which does analog to digital conversion and spits out a digital signal on the data pin with the temperature and humidity. 

DHT11 vs DHT22

both the DHT sensors look a bit similar and have the same pinout, but have different characteristics. Here are the specs:

DHT11 - 

•     Ultra low cost

•     3 to 5V power and I/O

•     2.5mA max current use during conversion (while requesting data)

•     Good for 20-80% humidity readings with 5% accuracy

•     Good for 0-50°C temperature readings ±2°C accuracy

•     No more than 1 Hz sampling rate (once every second)

•     Body size 15.5mm x 12mm x 5.5mm

•     4 pins with 0.1" spacing

DHT22 / AM2302 (Wired version) - 

•     Low cost

•     3 to 5V power and I/O

•     2.5mA max current use during conversion (while requesting data)

•     Good for 0-100% humidity readings with 2-5% accuracy

•     Good for -40 to 80°C temperature readings ±0.5°C accuracy

•     No more than 0.5 Hz sampling rate (once every 2 seconds)

•     Body size 15.1mm x 25mm x 7.7mm

•     4 pins with 0.1" spacing

DHT sensors have four pins

•     VCC - red wire Connect to 3.3 - 5V power

•     Data out - white or yellow wire

•     Not connected

•     Ground - black wire

DHTxx Sensor Library - 

Arduino IDE - Sketch→Include Library→Manage Libraries…

Enter “dht” in the search field and look through the list for “DHT sensor library by Adafruit.” Click the “Install” button, or “Update” from an earlier version.

Now select Examples→DHT→DHTtester sketch

 You should see the temperature in C and humidity. You can see changes by breathing onto the sensor which should increase the humidity.

You can add as many DHT sensors as you line on individual pins, just add new lines such as

DHT dht2 = DHT(pin, type);

below the declaration for the initial dht object, and you can reference the new dht2 sensor to get temperature in C and humidity data.