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There are two ways to setup MQTT.
1/ Running a python script.
2/ Using Emonhub.

Using Python Script

In this setup the Raspberrypi where the RPICT is will be the MQTT broker. A script will run to convert the serial string from the RPICT into channel feed.

Setup Mosquito broker

Install Mosquitto using the commands below:

sudo apt install -y mosquitto mosquitto-clients

Enable the service to start at boot time:

sudo systemctl enable mosquitto.service

Make the script

First of all install the mqtt python module

sudo pip install paho-mqtt

If not installed already install pip first with sudo apt-get install python-pip

A simple python script can be edited. Create a file with the content of the script below:

MQTT_SERV = "localhost"

CHANNELS = ["NodeID", "RP1", "RP2", "RP3", "RP4", "RP5", "RP6", "RP7",
		"Irms1", "Irms2", "Irms3", "Irms4", "Irms5", "Irms6", "Irms7",

import paho.mqtt.client as mqtt
import serial

client = mqtt.Client("P1")
client.username_pw_set(MQTT_USER, MQTT_PASS)

 	while 1:
 		# Read one line from the serial buffer
		 line = ser.readline()
	 	# Remove the trailing carriage return line feed
	 	line = line[:-2]
	 	# Create an array of the data
	 	Z = line.split(' ')
	 	# Print it for debug
	 	print line
		# Publish to the MQTT broker
 		for i in range(len(Z)):
 			client.publish("%s/%s" % (MQTT_PATH, CHANNELS[i]), Z[i]) 
except KeyboardInterrupt:

Modify the five parameters MQTT_SERV, MQTT_PATH, MQTT_USER, MQTT_PASS and CHANNELS to your needs. We are using a default RPICT7V1 for our example here.

Save the file and launch it with the command

python myfile.py

When running the above script all channels will be published as soon as data are sent by the RPICT board.

Test it

Test the channels by subscribing to one channel as below:

mosquitto_sub -h localhost -t RPICT7V1/Vrms -u "" -P ""

The value of Vrms will be printed on the terminal.

Using Emonhub

If the Emoncms image is used then MQTT is already setup. Simply use Emonhub.

Include the following config in the emonhub config.

    Type = EmonHubMqttInterfacer
        mqtt_host =
        mqtt_port = 1883
        mqtt_user = 'emonpi'
        mqtt_passwd = 'emonpimqtt2016'

        pubchannels = ToRFM12,
        subchannels = ToEmonCMS,

        # emonhub/rx/10/values format
        # Use with emoncms Nodes module
        node_format_enable = 1
        node_format_basetopic = emonhub/

        # emon/emontx/power1 format - use with Emoncms MQTT input
        # http://github.com/emoncms/emoncms/blob/master/docs/RaspberryPi/MQTT.md
        nodevar_format_enable = 1
        nodevar_format_basetopic = emon/

Make sure the config also include the sensor config for the RPICT. For our RPICT7V1 example this is:

   nodename = my_RPICT7V1
   hardware = RPICT7V1
      names = RP1, RP2, RP3, RP4, RP5, RP6, RP7, Irms1, Irms2, Irms3, Irms4, Irms5, Irms6, Irms7, Vrms
      datacode = 0
      scales = 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
      units =W,W,W,W,W,W,W,mA,mA,mA,mA,mA,mA,mA,V

Test the final setup using the command below:

mosquitto_sub -h localhost -t emon/my_RPICT7V1/Vrms -u emonpi -P emonpimqtt2016