Sending data to Ditto

In this case we will use a Raspberry Pi 3B with Raspbian buster OS connected to a DHT22 temperature and humidity sensor.

Setting up the Raspberry Pi

In the following image the pins of the Raspberry used are shown.

We will use pins 2, 6, 23 and 24.

Obtaining sensor data

To get the data from the sensor it is necessary to install its library.

sudo pip3 install Adafruit_DHT

We can test the operation of the sensor by creating a .py file with the following code (in our case it is called dht_code.py and I have placed it on the desktop).

import Adafruit_DHT
import time

SENSOR_DHT = Adafruit_DHT.DHT22
PIN_DHT = 24

while True:
    humedad, temperatura = Adafruit_DHT.read(SENSOR_DHT, PIN_DHT)
    if humedad is not None and temperatura is not None:
        print("Temp={0:0.1f}C Hum={1:0.1f}%".format(temperatura, humedad))
    else:
        print("Lecture fails, chech connection");
    time.sleep(3);

And we run it as follows:

cd Desktop/
python3 dht_code.py 

Installing Mosquitto on Raspberry

To send the data to DITTO we will use MQTT with the Mosquitto broker.

sudo wget http://repo.mosquitto.org/debian/mosquitto-repo.gpg.key
sudo apt-key add mosquitto-repo.gpg.key
cd /etc/apt/sources.list.d/
sudo wget http://repo.mosquitto.org/debian/mosquitto-buster.list
sudo -i
apt-get update
apt-get install mosquitto
apt-get install mosquitto-clients

With this we would already have Mosquitto installed on our Raspberry. To test it we can open two terminals, subscribe to a topic with one and publish to that topic with another.

mosquitto_sub -h localhost -t casa/comedor/temperatura

mosquitto_pub -h localhost -t casa/comedor/temperatura -m "Temperatura: 25ºC"

Configuring Mosquitto on raspberry

If we wanted to try to send and receive messages by MQTT between the raspberry and another device, we would have to configure the following.

1. From the main route of the Raspberry edit the Mosquitto configuration file.

sudo nano /etc/mosquitto/mosquitto.conf

1. Write these three lines at the end of the file to enable connections with any IP through port 1883 and configure authentication.

listener 1883 0.0.0.0

password_file /etc/mosquitto/passwd
allow_anonymous true

So that mosquito.conf would look like this:

# Place your local configuration in /etc/mosquitto/conf.d/
#
# A full description of the configuration file is at
# /usr/share/doc/mosquitto/examples/mosquitto.conf.gz

pid_file /run/mosquitto/mosquitto.pid

persistence true
persistence_location /var/lib/mosquitto/

log_dest file /var/log/mosquitto/mosquitto.log
log_type all
log_timestamp true

include_dir /etc/mosquitto/conf.d

listener 1883 0.0.0.0

password_file /etc/mosquitto/passwd
allow_anonymous true

1. Save the file with Ctrl-O, Enter and Ctrl-X.
2. Create a user with password using the following command. Replace USERNAME with the username you want. When you run it, it will ask you to enter a password, which will not be visible while you type it.

sudo mosquitto_passwd -c /etc/mosquitto/passwd USERNAME

1. Restart Mosquitto with the following command:

sudo systemctl restart mosquitto

Finally, we would have Mosquitto configured to receive and send from other IPs. To do this you have to add -u "USERNAME" and -P "PASSWORD" (including quotes) to the respective command.

For example (in this case being user both the user and the password):

mosquitto_sub -h 192.168.0.27 -u "usuario" -P "usuario" -t "/Raspberry/Sensores/DHT22"

Sending data to MQTT from Raspberry

To work with MQTT in python we will need to make use of Eclipse Paho.

sudo pip3 install paho-mqtt

Now, we will create a .py file that publishes the sensor data in the corresponding topic of MQTT. For this we have adapted the code example exposed in the following link to the DHT22 sensor with the Adafruit_DHT library and the requirements of MQTT.

How to use MQTT in Python (Paho)

In addition, the message sent by MQTT regarding the Ditto Protocol has been made following both the documentation and an example of use.

Things - Create-Or-Modify protocol specification

• Code to send sensor data to MQTT and Eclipse Ditto

  from paho.mqtt import client as mqtt_client
  import time
  import random
  import Adafruit_DHT
  import json
  
  #Constants to connect to MQTT
  broker = "IP OF MQTT"
  port = POR OF MQTT
  topic = "telemetry"
  client_id = f'python-mqtt-{random.randint(0, 1000)}'
  username = "raspberry_DHT22_1@ditto"
  password = "password"
  
  #Constantes para obtener información del sensor
  SENSOR_DHT = Adafruit_DHT.DHT22
  PIN_DHT = 24
  
  #Constantes para crear el mensaje de Eclipse Ditto
  DITTO_NAMESPACE = "raspberry";
  DITTO_THING_ID = "DHT22_1";
  
  def connect_mqtt():
      def on_connect(client, userdata, flags, rc):
          if rc == 0:
              print("Connected to MQTT Broker!")
          else:
              print("Failed to connect, return code %d\n", rc)
      # Set Connecting Client ID
      client = mqtt_client.Client(client_id)
      client.username_pw_set(username, password)
      client.on_connect = on_connect
      client.connect(broker, port)
      return client
  
  def publish(client):
       while True:
           time.sleep(1)
           msg = getValues();
           if msg is not None:
              result = client.publish(topic, msg)
              status = result[0]
              if status == 0:
                  print(f"Send '{msg}' to topic '{topic}'")
              else:
                  print(f"Failed to send message to topic {topic}")
  
  def getValues():
      humedad, temperatura = Adafruit_DHT.read(SENSOR_DHT, PIN_DHT)
      if humedad is not None and temperatura is not None:
          temp = "{0:0.1f}".format(temperatura)
          hum = "{0:0.1f}".format(humedad)
          output =  "{\"topic\": \""
          output += DITTO_NAMESPACE
          output += "/"
          output += DITTO_THING_ID
          output += "/things/twin/commands/modify\",\"headers\":{\"response-required\":false, \"content-type\":\"application/vnd.eclipse.ditto+json\"},"
          output += "\"path\": \"/features\", \"value\":{"
          output += sensorString("temperature", temp) 
          output += ","
          output += sensorString("humidity", hum)
          output += "}}"
          return output
      else:
          print("Failed on lecture, check circuit")
          return None
  
  def sensorString(name, value):
      return "\"" + name + "\": { \"properties\": { \"value\": " + value + "}}"; 
  
  def run():
      client = connect_mqtt()
      client.loop_start()
      publish(client)
  
  if __name__ == '__main__':
      run()

This code has been saved in a .py file with the name of dht22publisher.py and have saved it on the desktop. To execute it we use:

cd Desktop/
python3 dht22publisher.py