Mqtt Subscribing and reading from multiple topics

Question

I need to read two sensors and get the result on a pygame window. I have a pi zero running as publisher of the sensors and as broker. It creates two topics, "house" and "heat". On a second pi (jessie on virtualbox) I run the following python script and I get the results expected. Therefore I would ask if my choice of creating two different clients (with two different on_message) is a right choice, in order to get two values from two different topics. Please forgive me for errors in the code or inaccuracies, I'm not expert and I knew Mosquitto only a month ago. Most of this code is a raw code only for testing mqtt. Surfing the web I didn't found practical examples on how to read sensor values and put them in a window (like pygame or Tkinter), without using cloud apps and using python and pi's; does anybody know of such a tutorial? Thanks

import time
import paho.mqtt.client as paho
import pygame, sys

pygame.init()
screen = pygame.display.set_mode((640,480),0,32)
background = pygame.Surface(screen.get_size())
background.fill((0,0,0))
font = pygame.font.SysFont("comicsansms", 72)

broker = "192.168.100.21"

ss=''
tt=''
def omessage(client, userdata, message):
    if message.topic=="house":
        global ss
        ss=(str(message.payload.decode("utf-8")+message.topic))
    if message.topic=="heat":
        global tt
        tt=(str(message.payload.decode("utf-8")+message.topic))

client=paho.Client("cliente-001")
client.on_message=omessage
client.connect(broker)
client.loop_start()

client.subscribe("house")
client.subscribe("heat")
while True:
    screen.blit(background, (0,0))

    text=font.render(" %s" %ss, True, (0,255,0))
    textRect = text.get_rect()
    screen.blit(text,textRect)

    text1=font.render(" %s" %tt, True, (0,255,0))
    text1Rect = text1.get_rect(center=(150,150))
    screen.blit(text1,text1Rect)
    time.sleep(0.2)    
    pygame.display.update()
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()
pygame.quit()
sys.exit()

Your last suggestion made my code working as expected. I updated the above code with last edits. Many thanks!! — user3072083

hardillb hardillb · Accepted Answer · 2018-08-12T10:08:11

First, you should only be using one client
Second, you should subscribe to both topics once outside the loop
Third, use message.topic in the on_message callback to work out which topic the message was published on.

Mqtt Subscribing and reading from multiple topics

1 Answers