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):

1. Power to a 3.3V or 5V pin
2. Data to a regular GPIO pin
3. (skip this pin)
4. 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!