MQTT/Python Subscribe to multiple topics and write payloads on Raspberry LCD

Question

I'm new on Python and also on MQTT. I was able to write some Python working code to publish connected sensors data to a broker, now I'd like to subscribe to more than one topic and write all the payloads on an LCD 20x4 connected to a raspberry.

Actually I wrote a Python to subscribe on one topic and write the payload on the LCD; no problem, it's working. No way to include other topics in the same Python and write the payload on the LCD.

Following you can find my working Python code for "just" ONE topic.

#!/usr/bin/python
# -*- coding: utf-8 -*-
#
# RPi-S-LCD.py
# Created on 8/1/2017
#
# Python program that write payloads on LCD 20x4
#

import time
import sys
import os
import paho.mqtt.client as paho
sys.path.append("/home/pi/Adafruit_Python_CharLCD")
import Adafruit_CharLCD as LCD
import Adafruit_GPIO.MCP230xx as MCP

### Define MCP pins connected to LCD
lcd_rs = 6
lcd_en = 4
lcd_d4 = 3
lcd_d5 = 2
lcd_d6 = 1
lcd_d7 = 0
lcd_backlight = None

### Define LCD type
lcd_columns = 20
lcd_rows = 4

### Initialize MCP23017 for LCD
gpiomcp = MCP.MCP23017(0x20, busnum=1)

### Initialize LCD panel parameters
lcd = LCD.Adafruit_CharLCD(lcd_rs, lcd_en, lcd_d4, lcd_d5, lcd_d6, lcd_d7, lcd_columns, lcd_rows, lcd_backlight, gpio=gpiomcp)
lcd.show_cursor(False)
lcd.blink(False)
lcd.clear()

### Read data from MQTT broker
def on_subscribe(client, userdata, mid, granted_qos):
    print("Subscribed to the broker "+str(mid)+" "+str(granted_qos))


### Print topic data to LCD
def on_message1(client, userdata, msg):
    lcd.set_cursor(0,0)
    lcd.message(msg.payload)

client = paho.Client()
client.on_subscribe = on_subscribe
client.on_message = on_message1
client.connect("10.0.2.10", 1883, 30)
client.subscribe("iDomus/Time",2)

client.loop_forever()

Answer 1

reading more documentation on MQTT I found the function

"message_callback_add"

and now the python program is working fine. This is what I've had in mind. Now I subscribe to all topics but I choose what particular topic I want to treat and the payload is separated for an easy visualisation on LCD. Sorry for my python code.. I'm not a programmer but the following it's working fine for me. Hope it can help other people with my same problem.

#!/usr/bin/python
# -*- coding: utf-8 -*-
#
# RPi-S-LCD.py
# Created on 21/1/2017
#
# Python program that use LCD 20x4 to display topics info
#

import time
import sys
import os
import paho.mqtt.client as paho
sys.path.append("/home/pi/Adafruit_Python_CharLCD")
import Adafruit_CharLCD as LCD
import Adafruit_GPIO.MCP230xx as MCP

### Define MCP pins connected to LCD
lcd_rs = 6
lcd_en = 4
lcd_d4 = 3
lcd_d5 = 2
lcd_d6 = 1
lcd_d7 = 0
lcd_backlight = None

### Define LCD type
lcd_columns = 20
lcd_rows = 4

### Initialize MCP23017 for LCD
gpiomcp = MCP.MCP23017(0x20, busnum=1)

### Initialize LCD panel parameters
lcd = LCD.Adafruit_CharLCD(lcd_rs, lcd_en, lcd_d4, lcd_d5, lcd_d6, lcd_d7, lcd_columns, lcd_rows, lcd_backlight, gpio=gpiomcp)
lcd.show_cursor(False)
lcd.blink(False)
lcd.clear()

### DATE
def on_message_date(mosq, obj, msg):
    lcd.set_cursor(0,0)
    lcd.message(str(msg.payload))

### TIME
def on_message_time(mosq, obj, msg):
    lcd.set_cursor(0,2)
    lcd.message(str(msg.payload))

### RELAY
def on_message_relay(mosq, obj, msg):
    if (str(msg.payload)[3]) == '0':
        lcd.set_cursor(7,2)
        lcd.message("RL1= 0 RL2= 0")
    elif (str(msg.payload)[3]) == '1':
        lcd.set_cursor(7,2)
        lcd.message("RL1= 1 RL2= 0")
    elif (str(msg.payload)[3]) == '2':
        lcd.set_cursor(7,2)
        lcd.message("RL1= 0 RL2= 1")
    elif (str(msg.payload)[3]) == '3':
        lcd.set_cursor(7,2)
        lcd.message("RL1= 1 RL2= 1")
    else:
        lcd.set_cursor(7,2)
        lcd.message("RELAYs ERROR!")

### PUBLIC IP
def on_message_pubip(mosq, obj, msg):
    lcd.set_cursor(0,1)
    lcd.message("                    ")
    lcd.set_cursor(0,1)
    lcd.message("IP = "+str(msg.payload)[0:14])

### TEMPERATURE
def on_message_temp(mosq, obj, msg):
    lcd.set_cursor(0,3)
    lcd.message(str(msg.payload)[0:4]+chr(223)+"C")

### HUMIDITY
def on_message_humi(mosq, obj, msg):
    lcd.set_cursor(7,3)
    lcd.message(str(msg.payload)[0:4]+chr(37))

### PRESSURE
def on_message_pres(mosq, obj, msg):
    lcd.set_cursor(13,3)
    lcd.message(str(msg.payload)+"hPa")

### topic message
def on_message(mosq, obj, msg):
    print(msg.topic+" "+str(msg.qos)+" "+str(msg.payload))

mqttc = paho.Client()

#Add message callbacks that will only trigger on a specific   subscription    match
mqttc.message_callback_add('iDomus/Time', on_message_time)
mqttc.message_callback_add('iDomus/Date', on_message_date)
mqttc.message_callback_add('iDomus/PubIPRead', on_message_pubip)
mqttc.message_callback_add('iDomus/RPiS/Sens1/Temp', on_message_temp)
mqttc.message_callback_add('iDomus/RPiS/Sens1/Humi', on_message_humi)
mqttc.message_callback_add('iDomus/RPiN/Sens2/Pres', on_message_pres)
mqttc.message_callback_add('iDomus/RPiS/Rel1/Read', on_message_relay)
mqttc.on_message = on_message
mqttc.connect("10.0.2.10", 1883, 30)
mqttc.subscribe("iDomus/#")

mqttc.loop_forever()