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--- tutorials:learn:sensors:dht.html [2011/06/23 00:14]
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+++ tutorials:learn:sensors:dht.html [2016/01/28 18:05]
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-==== Introduction  ====
-[[http://www.ladyada.net/images/sensors/dhtsensors.jpg|{{  http://www.ladyada.net/images/sensors/dhtsensors_t.jpg?nolink&500x385  |}}]]
-This tutorial covers the low cost [[http://www.adafruit.com/category/35_66|DHT temperature & humidity sensors]]. These sensors are very basic and slow, but are great for hobbyists who want to do some basic data logging. The DHT sensors are made of two parts, a capacitive humidity sensor and a[[http://www.ladyada.net/learn/sensors/thermistor.html| thermistor.]] There is also a very basic chip inside that does some analog to digital conversion and spits out a digital signal with the temperature and humidity. The digital signal is fairly easy to read using any microcontroller.
-==== DHT11 vs DHT22  ====
-We have two versions of the DHT sensor, they look a bit similar and have the same pinout, but have different characteristics. Here are the specs:
-**[[http://www.adafruit.com/products/386|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
-**[[http://www.adafruit.com/products/385|DHT22]]**
-  *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 125°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
-As you can see, the [[http://www.adafruit.com/products/385|DHT22]] is a little more accurate and good over a slightly larger range. Both use a single digital pin and are 'sluggish' in that you can't query them more than once every second or two.
-**You can pick up both the [[http://www.adafruit.com/products/386|DHT11]] and DHT22 from the adafruit shop!**
-==== Connecting  ====
-[[http://www.ladyada.net/images/sensors/dhtbreadboard.jpg|{{  http://www.ladyada.net/images/sensors/dhtbreadboard_t.jpg?nolink&500x385  |}}]]
-Luckily it is trivial to connect to these sensors, they have fairly long 0.1"-pitch pins so you can plug them into any breadboard, perfboard or similar.
-==== Wiring  ====
-Likewise, it is fairly easy to connect up to the DHT sensors. They have four pins
-  *VCC (3 to 5V power)
-  *Data out
-  *Not connected
-  *Ground
-Simply ignore pin 3, its not used. You will want to place a 10K resistor between VCC and the data pin, to act as a medium-strength pull up on the data line. The Arduino has built in pullups you can turn on but they're very weak, about 100K
-This diagram shows how we will connect for the testing sketch. Connect data to pin 2, you can change it later to any pin.
-{{  http://www.ladyada.net/images/sensors/dhtwiring.gif?nolink&514x421  |}}
-==== Arduino library code  ====
-To test the sketch, we'll use an Arduino. You can use any micrcontroller that can do microsecond timing, but since its a little tricky to code it up, we suggest verifying the wiring and sensor work with an Arduino to start.
-[[https://github.com/adafruit/DHT-sensor-library|Begin by downloading the DHT library from our github repository.]] To download, click the **DOWNLOADS** button in the top right corner. Rename the uncompressed folder **DHT** and make sure that it contains the **dht.cpp** file and others. Then drag the **DHT** folder into the **//arduinosketchfolder///libraries/** folder. You may have to create that libraries sub-folder if it doesnt exist. Restart the IDE
-Now load up the **Examples->DHT->DHTtester** sketch
-{{  http://www.ladyada.net/images/sensors/dhttester.gif?nolink&566x600  |}}
-If you're using a **DHT11** sensor, comment out the line that sets the type:
- //#define DHTTYPE DHT22   // DHT 22  (AM2302)
-and uncomment the line that says
-#define DHTTYPE DHT11   // DHT 11
-This will make the data appear correctly for the correct sensor. Upload the sketch!
-{{  http://www.ladyada.net/images/sensors/dhtout.gif?nolink&539x376  |}}
-You should see the temperature and humidity. You can see changes by breathing onto the sensor (like you would to fog up a window) which should increase the humidity.
-==== Downloads!  ====
-  *[[https://github.com/adafruit/DHT-sensor-library|Arduino library and example code for DHT sensors]]
-  *[[http://www.adafruit.com/datasheets/DHT11-chinese.pdf|DHT11 datasheet ]](in chinese, so see the DHT22 datasheet too!)
-  *[[http://www.adafruit.com/datasheets/DHT22.pdf|DHT22 datasheet]]

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