In this example, we’ll use a Raspberry Pi and a DHT22 temperature and humidity sensor to print values on a web interface.



1. Hardware

Wire the DHT22 following the diagram. Note the resistor is a 10kΩ.



2. Software

OS : Linux Raspbian Jessie Lite.

2.1 Installation

Install the required software:

> apt-get update > sudo apt-get install build-essential python-dev git 1 2 > apt - get update > sudo apt - get install build - essential python - dev git

Install the library from Adafruit :

> git clone https://github.com/adafruit/Adafruit_Python_DHT.git > cd Adafruit_Python_DHT/ > sudo python setup.py install 1 2 3 > git clone https : / / github .com / adafruit / Adafruit_Python_DHT .git > cd Adafruit_Python_DHT / > sudo python setup .py install

2.2 Tests

> cd ~ > vi test.py 1 2 > cd ~ > vi test .py

And paste the following :

#!/usr/bin/python import Adafruit_DHT # Adafruit_DHT.DHT11, Adafruit_DHT.DHT22 or Adafruit_DHT.AM2302. sensor = Adafruit_DHT.DHT22 pin = 4 humidity, temperature = Adafruit_DHT.read_retry(sensor, pin) if humidity is not None and temperature is not None: print 'Temp={0:0.1f}*C Humidity={1:0.1f}%'.format(temperature, humidity) else: print 'Failed to get reading. Try again!' 1 2 3 4 5 6 7 8 9 10 11 12 #!/usr/bin/python import Adafruit_DHT # Adafruit_DHT.DHT11, Adafruit_DHT.DHT22 or Adafruit_DHT.AM2302. sensor = Adafruit_DHT . DHT22 pin = 4 humidity , temperature = Adafruit_DHT . read_retry ( sensor , pin ) if humidity is not None and temperature is not None : print 'Temp={0:0.1f}*C Humidity={1:0.1f}%' . format ( temperature , humidity ) else : print 'Failed to get reading. Try again!'

Make it executable :

> chmod +x test.py 1 > chmod + x test .py

And run it :

> sudo ./test.py Temp=30.7*C Humidity=38.9% 1 2 > sudo . / test .py Temp = 30.7 * C Humidity = 38.9 %

Working !

3. Web UI

3.1 Required software

Install the required software :

> sudo apt-get install python-pip > sudo pip install flask 1 2 > sudo apt - get install python - pip > sudo pip install flask

3.2 Main file

Edit the file :

> vim main.py 1 > vim main .py

With this content :

#!/usr/bin/python from flask import Flask, render_template import Adafruit_DHT app = Flask(__name__) sensor = Adafruit_DHT.DHT22 pin = 4 @app.route("/") def main(): humidity, temperature = Adafruit_DHT.read_retry(sensor, pin) templateData = { 'temperature' : temperature, 'humidity': humidity } return render_template('main.html', **templateData) if __name__ == "__main__": app.run(host='0.0.0.0', port=80, debug=True) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 #!/usr/bin/python from flask import Flask , render_template import Adafruit_DHT app = Flask ( __name__ ) sensor = Adafruit_DHT . DHT22 pin = 4 @ app . route ( "/" ) def main ( ) : humidity , temperature = Adafruit_DHT . read_retry ( sensor , pin ) templateData = { 'temperature' : temperature , 'humidity' : humidity } return render_template ( 'main.html' , * * templateData ) if __name__ == "__main__" : app . run ( host = '0.0.0.0' , port = 80 , debug = True )

Make it executable :

> chmod +x server.py 1 > chmod + x server .py

3.2 Template

Edit the template file :

> vi templates/main.html 1 > vi templates / main .html

With this content :

<!doctype html> <html> <head> <title>Dynamic Resize</title> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <style> body { text-align: center; padding: 0px; margin: 0px; } .clear:before, .clear:after { content: ""; display: table; } .clear:after { clear: both; } .clear { *zoom: 1; } .wrapper { position: absolute; top: 0; right: 0; bottom: 0; left: 0; margin: 30px; border: 1px solid #cccccc; } .gauge { display: block; float: left; } #g1 { width: 50%; } #g2 { width: 50%; } </style> </head> <body> <div class="wrapper clear"> <div id="g1" class="gauge"></div> <div id="g2" class="gauge"></div> </div> <script src="{{ url_for('static', filename='raphael-2.1.4.min.js') }}"></script> <script src="{{ url_for('static', filename='justgage.js') }}"></script> <script> document.addEventListener("DOMContentLoaded", function(event) { var g1, g2, g3; var g1 = new JustGage({ id: "g1", value: {{temperature}}, min: 0, max: 50, title: "Temperature", }); var g2 = new JustGage({ id: "g2", value: {{humidity}}, min: 0, max: 100, title: "Humidity", }); }); </script> </body> </html> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 < ! doctype html > < html > < head > < title > Dynamic Resize < / title > < meta http - equiv = "Content-Type" content = "text/html; charset=UTF-8" / > <style> body { text-align : center ; padding : 0px ; margin : 0px ; } .clear:before, .clear:after { content : "" ; display : table ; } .clear:after { clear : both ; } .clear { *zoom : 1 ; } .wrapper { position : absolute ; top : 0 ; right : 0 ; bottom : 0 ; left : 0 ; margin : 30px ; border : 1px solid #cccccc ; } .gauge { display : block ; float : left ; } #g1 { width : 50% ; } #g2 { width : 50% ; } </style> < / head > < body > < div class = "wrapper clear" > < div id = "g1" class = "gauge" > < / div > < div id = "g2" class = "gauge" > < / div > < / div > <script src = "{{ url_for('static', filename='raphael-2.1.4.min.js') }}" > </script> <script src = "{{ url_for('static', filename='justgage.js') }}" > </script> <script> document . addEventListener ( "DOMContentLoaded" , function ( event ) { var g1 , g2 , g3 ; var g1 = new JustGage ( { id : "g1" , value : { { temperature } } , min : 0 , max : 50 , title : "Temperature" , } ) ; var g2 = new JustGage ( { id : "g2" , value : { { humidity } } , min : 0 , max : 100 , title : "Humidity" , } ) ; } ) ; </script> < / body > < / html >

3.3 Static files

I use the files from justGage.com :

> wget http://justgage.com/download/justgage-1.2.2.zip > unzip justgage-1.2.2.zip > mkdir static > cp justgage-1.2.2/*.js static/ 1 2 3 4 > wget http : / / justgage .com / download / justgage - 1.2.2.zip > unzip justgage - 1.2.2.zip > mkdir static > cp justgage - 1.2.2 / * .js static /

3.4 Run

Then we can run :

> sudo ./main.py * Running on http://0.0.0.0:80/ (Press CTRL+C to quit) * Restarting with stat * Debugger is active! * Debugger pin code: 867-781-657 192.168.137.1 - - [20/Mar/2016 10:47:04] "GET / HTTP/1.1" 200 - 192.168.137.1 - - [20/Mar/2016 10:47:04] "GET /static/raphael-2.1.4.min.js HTTP/1.1" 200 - 192.168.137.1 - - [20/Mar/2016 10:47:04] "GET /static/justgage.js HTTP/1.1" 200 - 1 2 3 4 5 6 7 8 > sudo . / main .py * Running on http : / / 0.0.0.0 : 80 / ( Press CTRL + C to quit ) * Restarting with stat * Debugger is active ! * Debugger pin code : 867 - 781 - 657 192.168.137.1 - - [ 20 / Mar / 2016 10 : 47 : 04 ] "GET / HTTP/1.1" 200 - 192.168.137.1 - - [ 20 / Mar / 2016 10 : 47 : 04 ] "GET /static/raphael-2.1.4.min.js HTTP/1.1" 200 - 192.168.137.1 - - [ 20 / Mar / 2016 10 : 47 : 04 ] "GET /static/justgage.js HTTP/1.1" 200 -

Then open a browser and go to X.X.X.X:80 (replace by the Pi IP) :



