DHT11/22 Temperature Sensors using the WebIOPi REST API
I have been really impressed with the WebIOPi REST API, I am using it to control my garage door. However WebIOPi doesn't support the DHT11/DHT22 tempreature sensors natively. In this guide I will walk you through the steps to get an endpoint to return temperature and humidity data via the WebIOPi REST API.
Step 1: Install the sensor
I followed these wiring instructions to get my DHT11 sensor plugged into my Raspberry Pi. He basically says to connect the pins like this (left to right):
- Power to a 3.3V or 5V pin
- Data to a regular GPIO pin
- (skip this pin)
- Ground to a Ground pin
I also connected a pull-up 10K resistor between the Power and Data wires.
Step 2: Install Adafruit's DHT library
Since WebIOPi doesn't support the DHT11/DHT22 sensors natively, we have to install a driver that can read from it. I was able to get Adafruit's DHT library working pretty easily:
apt-get update
sudo apt-get install build-essential python-dev
git clone https://github.com/adafruit/Adafruit_Python_DHT.git
sudo python setup.py install
Optional: Test your sensor
If you would like to test your sensor, you can do so like this:
sudo python examples/AdafruitDHT.py 11 4
- Change the first number to 22 if you have the DHT22 sensor.
- Change the second number to the GPIO pin you have your sensor on.
You should see something like:
Temp=15.0*C Humidity=45.0%
Step 3: Install WebIOPi using Python 2.7
By default, WebIOPi installs itself using Python 3. Unfortunately Python 3 is not widely adopted and many developers prefer to work in Python 2.7--The driver we will be using for the DHT11 requires Python 2.7.
Installing WebIOPi using Python 2.7 is easy, we just have to remove " python3" from the fourth line setup.sh:
$ wget WebIOPi-x.y.z.tar.gz
$ tar xvzf WebIOPi-x.y.z.tar.gz
$ cd WebIOPi-x.y.z
$ sed -i 's/ python3//' setup.sh
$ sudo ./setup.sh
$ sudo webiopi-passwd
$ sudo service webiopi restart
Now if you go to http://(raspbery.pi.ip):8000/app/gpio-header and login using the user and password you just set, you should see a graphical representation of your Pi's GPIO header.
Step 4: Set up a WebIOPi Macro
To get the WebIOPi REST API to return the temperature and humidity data, we are going to set up a macro:
$ cd ~
$ pico temperature.py
Paste in the following:
#!/usr/bin/env python
import webiopi
import Adafruit_DHT
import json
SENSOR = Adafruit_DHT.DHT11
PIN = 24
@webiopi.macro
def temperature():
humidity, temperature = Adafruit_DHT.read_retry(SENSOR, PIN)
if humidity is not None and temperature is not None:
fahrenheit = 9.0 / 5.0 * temperature + 32
return json.dumps({
"temperature": fahrenheit,
"humidity": humidity
})
else:
return False
Change SENSOR and PIN if necessary. If you want the temperature in Celcius, remove line 13 and change line 15 to: "temperature": temperature
The last step is to add this file to the WebIOPi config:
$ sudo pico /etc/webiopi/config
Find the [SCRIPTS] section and add:
temperature = /home/pi/temperature.py
Then restart webiopi:
sudo service webiopi restart
Testing the endpoint
All thats left now is to test the WebIOPi macro. Here's an example using cURL:
$ curl -X POST -u webiopi:(password) localhost:8000/macros/temperature
You should see something like this:
{"temperature": 60.8, "humidity": 45.0}
There you have it! You can now read temperature and humidity data from your DHT11 or DHT22 sensor using WebIOPi!
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