DHT22 on Raspberry Pi as a REST API

This is a simple python (flask) application that exposes the values read from a DHT22 (connected to Raspberry Pi GPIO) via a REST API.

Uses Adafruit's DHT Library to access the data on the GPIO.

Installation

Step 1: Virtualenv Setup

Create a virtualenv for our python stuff (to isolate from other python things):

virtualenv flask

If you do not have virtualenv installed, follow the instructions here.

Step 2: Install DHT Library

Install the DHT Library using the flask virtual env:

 git clone https://github.com/adafruit/Adafruit_Python_DHT.git adafruit-python-dht
 cd adafruit-python-dht
 ../flask/bin/python setup.py install
 cd -

TIP: If you get an error during the last step, you are most likely not running it on supported hardware (Raspberry Pi/Beaglebone). To install it on unsupported hardware, you can use the --force-test flag.

Step 3: Installation other dependencies

flask/bin/pip install -r requirements.txt

Usage

To start the application, simply do:

./app.py

The following REST endpoints are exposed:

• http://localhost:5000/api/v1/temperature
• http://localhost:5000/api/v1/humidity
• http://localhost:5000/api/v1/temperature+humidity

Example Output

{
  "humidity": 33.400001525878906,
  "name": "Buero",
  "temperature": 23.299999237060547,
  "timestamp": "2017-04-25T09:05:15.162306"
}

Configuration

This applicaiton assumes that the DHT22 data pin is pin 5 on the Raspberry GPIO. This setting can be changed by passing in the --gpio-pin command line parameter.

Alongside the --gpio-pin there are the following command line parameters available

Flag	Description	Default
-H, --host	Defines the host the application is exposed on.	127.0.0.1
-P, --port	Defines the port port the application is exposed on.	5000
-N, --sensor_name	Defines the name of the sensor used in the name field in the API response. Can be used to set a unique name to better differentiate between multple sensors/instances.	Sensor
-G, --gpio-pin	Defines which pin will be accessed to read the DHT data	4

Run as a service

This assumes, that the repository was cloned to /opt/simonalbrecht/raspberry-pi-dht22-rest-api/ and the virtualenv name is flask.

Copy the file etc/systemd/system/[email protected] to /etc/systemd/system/ on the Raspberry Pi to which the DHT22 sensor is connected. Change the command line parameters (GPIO pin, sensor name, port etc) on the ExecStart line to match your setup.

Reload the systemd daemon to make it aware of the new service:

sudo systemctl --system daemon-reload

And finally, enable (start on boot automatically) and start it:

sudo systemctl enable dht22-rest-api@pi
sudo systemctl start dht22-rest-api@pi

To check the status of the service, use:

sudo systemctl status dht22-rest-api@pi

For the logs, run:

 sudo journalctl -f -u dht22-rest-api@pi