MQTT with 2 subscribes

[luc hanneuse]

Hi,
I'm new to micropython. I've taken several examples on this forum, assemble them and succeed to subscribe to 2 differents mqtt topics. But how can I put the differnts message in 2 variables like sensor21 and sensor31 ?

from mqtt import MQTTClient
import machine
import time
import pycom

def sub_cb(topic, msg):
   print(msg)

wlan = WLAN(mode=WLAN.STA)
wlan.connect("wifi", auth=(WLAN.WPA2, "pass"), timeout=5000)

while not wlan.isconnected():
    machine.idle()
print("Connected to Wifi\n")

client = MQTTClient("device_id", "192.168.0.20",user="pi", password="raspberry", port=1883)

client.set_callback(sub_cb)
client.connect()

wifiaddress = ((str(wlan.ifconfig()[:1]))[2:])[:-3]
client.publish(topic="lopy/ip", msg=wifiaddress)

client.subscribe(topic="pi/sensor21/temperature")
client.subscribe(topic="pi/sensor31/temperature")

def t3_publication(topic, msg):
    print (topic, ':', msg)
    #pycom.rgbled(0xff00)

client.set_callback(t3_publication)

while True:
    client.check_msg()

Thanks

[luc hanneuse]

@luc-hanneuse
anyone ?

[livius]

@luc-hanneuse
what is your output from
print (topic, ':', msg)?

[luc hanneuse]

@livius
So it subscribes correctly to the 2 topics. But I can't succeed in putting each message in a different variable.

Here is my output :
b'pi/sensor21/temperature' : b'21.00'
b'pi/sensor31/temperature' : b'25'

[luc hanneuse]

@luc-hanneuse

I've tried this, but I got an error message.

one="pi/sensor21/temperature"
two="pi/sensor31/temperature"

client.subscribe(topic=one)
client.subscribe(topic=two)

def mytopic(topic, msg):
    print (topic, ':', msg)

    if topic == one:
        b = (msg[0]-48)*10+(msg[1]-48)

    if topic == two:
        c = (msg[0]-48)*10+(msg[1]-48)
    s.send(bytes([b,c]))
    #print("Sigfox sent\n")

[livius]

@luc-hanneuse
what is the error message?
and to convert from text to number simply do

v2=float(v)

or if you need only integer part

v2=int(float(v))

[luc hanneuse]

@livius
For the conversion, It doesn't work :

v2=float(v)

I've got an error
can't convert bytes to float

v2=int(v)

I've got an error
ValueError: invalid syntax for integer with base 10

For the previous code, the error is
NameError: local variable referenced before assignment

[chumelnicu]

@luc-hanneuse Try to pack that two data (temperatures ) in to json format and publising after to MQTT broker

[luc hanneuse]

@chumelnicu

It comes from different devices publishing each one their temperatures.

[livius]

@luc-hanneuse said in MQTT with 2 subscribes:

For the previous code, the error is
NameError: local variable referenced before assignment

You got this error because you do this

s.send(bytes([b,c]))

but in the code you have if variants and one of two "b" or "c" is unassigned
because you got 2 events - look how your code work by changing it to:

def mytopic(topic, msg):
    print("---start---")
    print (topic, ':', msg)

is your output now like this?

"---start---"
b'pi/sensor21/temperature' : b'21.00'
"---start---"
b'pi/sensor31/temperature' : b'25'

you must put b and c outside of procedure
and inside test if both "b" and "c" have values and only then send it
but this can also cause minssing values if you got only "b" and once again "b" and next "c"
PS> about simple conversion i am writing about string, if it is a bytes then
you must catch it e.g. v2=float(str(v))
but your way should work also byte-48{0ascii} *10...

[luc hanneuse]

@livius said in MQTT with 2 subscribes:

you must put b and c outside of procedure

How can I get those variable out of "def"?

[livius]

@luc-hanneuse said in MQTT with 2 subscribes:

How can I get those variable out of "def"?

msg_b= None
msg_c= None

def mytopic(topic, msg):
  global msg_b
  global msg_c
  ...

[luc hanneuse]

Finally some improvements, thanks for your help.
I succeed to subscribe to several topics and get some results.

topic_sub=["pi/sensor21/temperature","pi/sensor40/temperature","pi/sensor02/temperature","pi/sensor12/in_01","pi/sensor12/out_01"]
topic_length=len(topic_sub)
val= [0,0,0,0,0] #should be a better way to create this array from topic_length
update = None # used if you want to send a signal without waiting the 800s cycle

for i in range(0, topic_length):
    client.subscribe(topic=topic_sub[i])

def mytopic(topic, msg):
    global update
    global topic_length
    global topic_sub
    global val

    if ubinascii.hexlify(topic) == ubinascii.hexlify(topic_sub[0]):
        val[0] = (msg[0]-48)*10+(msg[1]-48) #ascii-to-int, to be improved
        val[0] = val[0] % 255 #sure to be a byte

    if ubinascii.hexlify(topic) == ubinascii.hexlify(topic_sub[1]):
        val[1] = (msg[0]-48)*10+(msg[1]-48) #ascii-to-int, to be improved
        val[1] = val[1] % 255 #sure to be a byte

    if ubinascii.hexlify(topic) == ubinascii.hexlify(topic_sub[2]):
        val[2] = (msg[0]-48)*10+(msg[1]-48) #ascii-to-int, to be improved
        val[2] = val[2] % 255 #sure to be a byte

    if ubinascii.hexlify(topic) == ubinascii.hexlify(topic_sub[3]):
        val[3] = (msg[0]-48) #ascii-to-int, to be improved
        update = 1

    if ubinascii.hexlify(topic) == ubinascii.hexlify(topic_sub[4]):
        val[4] = (msg[0]-48) #ascii-to-int, to be improved
        update = 1

client.set_callback(mytopic)

chrono = Timer.Chrono()
chrono.start()

while True:
    client.check_msg()
    if chrono.read()%60 < 5 and blink == 0:#just a blinking
        pycom.rgbled(0x0064)
        blink = 1
        print(".")

    if chrono.read()%60 > 5 and blink == 1:#just a blinking
        pycom.rgbled(0x0000)
        blink = 0
        print("-")

    if chrono.read() > 800:#wait 800s to avoid the sigfox message limit per day
        pycom.rgbled(0x007f00)
        s.send(bytes(val))
        print("Sigfox sent\n")
        chrono.reset()
        pycom.rgbled(0x0000)

    if update == 1:#send immediately if update is triger
        pycom.rgbled(0x007f00)
        s.send(bytes(val))
        print("Sigfox sent\n")
        chrono.reset()
        update = 0
        pycom.rgbled(0x0000)

But the exact nature of the result of topic and message are unknown. Is it a string, a byte,... ?
Most conversions don't works. I've tried float() or int() and get errors

I still have errors, certainly related to that problem :
And I've got the following message error when

s.send(bytes(val))
#val is filled with the several message of the topics

The packet is correctly sent, but the program quit with the following error message OSError: [Errno 100] ENETDOWN

When I send the following code, I've no error

val = [1,2,3,4,5]
s.send(bytes(val))

[livius]

@luc-hanneuse said in MQTT with 2 subscribes:

unknown. Is it a string, a byte,... ?

unknown = None?
if yes than it mean no value at all.

And before send put print command to see what you tried to send

print(str(val))
s.send(bytes(val))

and if you still have problem show what was printed

[luc hanneuse]

@livius

The "topic" and "message" variables are created by the mqtt library.
And yes, those variables don't react like string, byte,... most of the variables conversion don't work. That's why I called them "unknown".

I've already print them, but that doesn't help to clarify the type of variable.

[livius]

@luc-hanneuse
first you can try to test if it is None

if v==None:

and also you can test for type by:

type(v)