Having trouble using the mqtt broker to publish data to genmon.

[tomjoegenerator]

Checklist

• I made sure that there are no existing issues or discussions - open issues,closed issues,open discussion, closed discussion - which may answer my question or that I could contribute my information to.
• I have read the Known Issues Wiki Page and my question / issue is not listed.
• I have provided the version of the software and the operating system in my post.
• If I have an issue with genmon not communicating with the controller, I have read and followed the serial troubleshooting guide.

Version

Version V1.19.03

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I have not submitted logs

What is/are your question(s)?

Tom and I are developing an add on to genmon to read the oil pressure from a bellows sensor using an ADC and uploading it to a mqtt broker to be displayed in genmon as a gauge. I have included a copy of the program and all is working fine except an issue with persistent data being displayed.

What is happening is if our program is running data is being pushed to the mqtt server and it is being displayed. Now if for some reason the program crashes or is killed, the last data pushed to the mqtt server continue to be displayed. This is misleading, say the pressure was 35 psi and all is well, if the program stops the last value continue to be displayed until the program is restarted.

I am new to using a mqtt broker and I am assuming that after a value is read it is marked and should not be read again. Am I missing something when pushing my message to the mqtt broker so that it is not persistent, or is there an internal problem with genmon? Could genmon be setting a variable and not clearing it until a new value is read.

Any help would be appreciated.
Joe

Additional information

version_2.4 Removed a lot of extra code and made it more readable.

SPDX-FileCopyrightText: 2023 Joseph Sundermier, Thomas Crist

SPDX-License-Identifier: MIT

This program is a supplement to the genmon program. Once started it will:

Write out the the date and time it was started to a userdefined.json file to be displayed on the monitor page

Regullary read voltage drop across a transducer using a MCP3008 ADC over the SPI bus.

Convert the voltage to an oil pressure using an exponential fit.

Publish it to a mqtt server to be used by the genmon program to be display as a gauge on the status page.

import Adafruit_GPIO.SPI as SPI
import Adafruit_MCP3008
import paho.mqtt.client as mqtt
import json
import os
import time
from datetime import datetime

#mqttBroker = "localhost"
mqttBroker = "127.0.0.1"
mqttTopic = "Oil pressure"

client = mqtt.Client(mqttTopic)
client.connect(mqttBroker)

Software SPI configuration,these are my pins convential is (clk=11, cs=1, miso=9, mosi=10), these can be changed to meet your requirements.

mcp = Adafruit_MCP3008.MCP3008(clk=11, cs=8, miso=9, mosi=10)

Function to read the ADC

def readADC():

Read ADC in difference mode using pins 0 and 1, then convert to a voltage.

value = mcp.read_adc_difference(0)
voltage = value * 3.3 / 1027

Convert voltage to pressure using a power function a=261.27 and b=1.7026.

pressure = 261.27 * pow(voltage, 1.7026)
pressure = int(pressure)
return pressure

Function to get the current date and time.

def dateTime():
now = datetime.now()
now = now.strftime("%A %B %d, %Y %H:%M:%S")
return now

Modifies or creates the userdefined.json file with the last started time, run only once..

data = {'Oil Pressure program last started': dateTime()}
with open('userdefined.json', 'w') as f:
json.dump(data, f)
f.close()

Main loop, keep publishing current oil pressure reading to mqtt broker

while (True):
client.publish("Oil pressure", readADC())
time.sleep(1)

[jgyates]

I am assuming you are using the MQTT Sensor Input add on to get the data into genmon.

They way you describe it is the way I except it to work. MQTT brokers do not keep up with state of a sensor being read or not as it can be read by multiple endpoints. Most MQTT broker implementations are optimized to only transmit to end points that subscribe to a sensor topic (in this case genmon) if the sensor has changed. Your code publishes every second, but genmon will only see the updates that change. This minimizes network traffic. The actual sensor should be responsible for the data, otherwise any endpoint. displaying it would need to know about default values (e.g. zero for oil pressure and zero for a temperature sensor indicate wildly different conditions).

Genmon could add a feature that resorts to a default value, but that would be unique for each sensor potentially. Genmon could also remove the sensor if it does not report after a period of time, but that would require a reload of the gauge array and I am not liking the downstream ramifications of that to the maintenance of the code.

I think a better solution would be to add two things to your code.

1. an exception handler in the while loop to make any exceptions non fatal
2. a signal handler so you can publish the value you want when your code exits

For the exception handler:
The code you post will generate an exception (and stop working) if the MQTT broker is rebooted or restarted, or if there is any error when reading the ADC. The first thing I would do it to add some exception handling to make this a bit more tolerant of errors.

 client.loop_start().  # this allows PahoMQTT python library to reconnect if server connection is broken

  while (True):
       try:
             client.publish("Oil pressure", readADC())
             time.sleep(1)
       except Exception as e1:
              # you can log any errors here, e.g. print("Error: " + str(e1))
              time.sleep(10).  # wait for 10 seconds try again

For the signal handler add these lines to your code:

     import signal

After the initialization but before the while loop call this:

        signal.signal(signal.SIGTERM, SignalClose)  
        signal.signal(signal.SIGINT, SignalClose)

Then add a function named SignalClose

 def SignalClose():
        
        try:
               client.publish("Oil pressure", 0).  #publish a zero value
               time.sleep(1)
               client.loop_stop(force=True).   # stop the internal poll thread for paho client
       except Exception as e1:
              pass
              # you can log any errors here, e.g. print("Error: " + str(e1))

I suspect that this will solve most of your issues. Let me know if you have any questions.