Error publishing sensor data to Thingspeak using MQTT on Raspberry Pi

Question

I have connected a soil moisture sensor module and an LDR to an ADS1115 ADC (which is in turn connected to my R Pi). Am using Python 2.7. The ADC works fine and it prints values from channel 0 and channel 1 for the soil moisture module and the LDR respectively. I have the following codes to send data from the soil moisture module to Thingspeak using the following guides: https://www.mathworks.com/help/thingspeak/use-raspberry-pi-board-that-runs-python-websockets-to-publish-to-a-channel.html

https://github.com/adafruit/Adafruit_Python_ADS1x15

import time
import sys
from time import sleep
import paho.mqtt.publish as publish
import Adafruit_ADS1x15

#GPIO.setmode(GPIO.BOARD)

#Start of user config

channelID= "377509"
apiKey= "<APIKEY>"


#MQTT Connection Methods

useUnsecuredTCP= True

useUnsecuredWebsockets= False

useSSLWebsockets= False

mqttHost= "mqtt.thingspeak.com"

# You can use any Username.
mqttUsername = "SoilHumidityRpiDemo"

# Your MQTT API Key from Account > My Profile.
mqttAPIKey ="<APIKEY>"

if useUnsecuredWebsockets:
 tTransport= "websockets"
 tPort= 80

#Create topic string
topic= "channels/" + channelID + "/publish/" + apiKey


# Create an ADS1115 ADC (16-bit) instance.
adc = Adafruit_ADS1x15.ADS1115()

GAIN = 1

print('Reading ADS1x15 values, press Ctrl-C to quit...')

while True:
    m = adc.read_adc(0, gain=GAIN)
    print('Moisture Level:{0:>6}'.format(m))
    time.sleep(1)
    tPayload= "field1=%s" % m
    try:
      publish.single(topic, payload=tPayload, hostname=mqttHost, port=tPort, transport= tTransport,auth={'username':mqttUsername,'password':mqttAPIKey})
    except KeyboardInterrupt:
        break
    except:
        print ("There was an error publishing the data")

When I execute it, the error message "There was an error publishing the data" shows up. However when I just run a script to print the soil moisture values from the ADC on the terminal(without the codes to send data to Thingspeak via MQTT), that script works well.

Please change your except clause to except Exception as e: print(e) so you can learn more about what goes wrong. — nos
Thanks. I did as you said. I am getting this error: name 'tPort' is not defined — Tia

hardillb hardillb · Accepted Answer · 2018-01-17T09:24:00

The problem is because tPort and tTransport are only defined if useUnsecuredWebsockets is True

Since useUnsecuredWebsockets is set to False a few lines before this will never happen.

You can either change useUnsecuredWebsockets to True or add a else clause to the if statement to set the default values.

if useUnsecuredWebsockets:
 tTransport= "websockets"
 tPort= 80
else:
 tTransport = "tcp"
 tPort= 1883

Error publishing sensor data to Thingspeak using MQTT on Raspberry Pi

1 Answers