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henriquesalvador

Domotz Eyes with Custom OIDs - Temperature monitoring example

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henriquesalvador

I have a Fish Tank with a temperature sensor installed on a Raspberry Pi Zero W that I wanted to monitor with Domotz Pro to receive push and emails alerts when the temperature is too high or too low. This is what I did:

 

The sensor is the DS18B20.

 

image.png

 

 I wired it to the Raspberry Pi Zero this way:

 

image.png

 

image.png

 

So I enabled OneWire support to read the sensor data:

 

Add to the end of the file /boot/config.txt this line:

 

dtoverlay=w1-gpio

 

And restart the system:

 

$init 6

 

To find out if the sensor was correctly recognized go to the folder /sys/bus/w1/devices/ and confirm that a 28-XXXXX folder has been created:

 

$ cd /sys/bus/w1/devices/
$ ls
28-02079245a4ec  w1_bus_master1

 

To read the temperature see the contents of the w1_slave file inside this folder:


pi@FishTank:/sys/bus/w1/devices $ cd 28-02079245a4ec
pi@FishTank:/sys/bus/w1/devices/28-02079245a4ec $ cat w1_slave
bd 01 55 05 7f 7e 81 66 42 : crc=42 YES
bd 01 55 05 7f 7e 81 66 42 t=27812

 

At that moment the water temperature was 27.812 Celsius.

 

I'm using this script in Python (/home/pi/temp_snmp.py) to get the temperatures:

 

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import os
import glob
import time

os.system('modprobe w1-gpio')
os.system('modprobe w1-therm')
base_dir = '/sys/bus/w1/devices/'
device_folder = glob.glob(base_dir + '28*')[0]
device_file = device_folder + '/w1_slave'
def read_temp_raw():
  f = open(device_file, 'r')
  lines = f.readlines()
  f.close()
  return lines
def read_temp():
  lines = read_temp_raw()
  while lines[0].strip()[-3:] != 'YES':
    time.sleep(0.2)
    lines = read_temp_raw()
  equals_pos = lines[1].find('t=')
  if equals_pos != -1:
    temp_string = lines[1][equals_pos+2:]
    temp_c = float(temp_string) / 1000.0
    temp_c = round(temp_c, 2)
#    temp_f = temp_c * 9.0 / 5.0 + 32.0
    return temp_c
#   return temp_f
temp = read_temp()
print temp

 

There are several other sensors that you can use with the Raspberry Pi, just create a script that print the current temperature.

 

To create the OID make sure that you have installed the snmp packages:

 

$sudo apt-get install snmp snmpd

 

Add to the end of the file /etc/snmp/snmpd.conf:

 

pass .1.3.6.1.2.1.25.1.7.1 /bin/sh /home/pi/temp_snmp.sh -g

 

Create the script file /home/pi/temp_snmp.sh with the following content:

 

#!/bin/bash

if [ "$1" = "-g" ]

then

echo .1.3.6.1.2.1.25.1.7.1

echo integer #set the OID as INTEGER

python -u /home/pi/temp_snmp.py #it will print the actual temperature.

fi

exit 0

 

Now, stop the snmpd service and run it using your actual user (if something goes wrong check the log file errlog.txt):

 

$sudo service snmpd stop

$snmpd -Lf errlog.txt

 

And confirm that everything is working fine:

 

$ snmpget -v2c -c public 127.0.0.1 .1.3.6.1.2.1.25.1.7.1

iso.3.6.1.2.1.25.1.7.1 = INTEGER: 28

 

As you can see, every time you read the OID .1.3.6.1.2.1.25.1.7.1 it will run the script that will return the temperature value.

 

Now you can setup the Domotz Eyes to read the SNMP sensor and create the Alerts:

 

image.pngimage.png

 

Following this same example you can create your own SNMP sensors and monitor them using your Domotz Pro agent.

 

This way I can receive alerts whenever the temperature goes down or increases too much:

 

image.png

 

To better understand the syntax used in the snmpd.conf  file refer to the man page (man snmpd.conf).

 

Do not hesitate to comment or share your own project in our community.

 

Henrique Salvador

Domotz Support

 

 

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GregS

We did something very similar to this last year for monitoring rack temperatures, but found that Domotz did not check snmp often enough to make it useful for things like that. It was randomly between 30-55 minutes. 

Have they updated that now? I've lost track of most of the features in Domotz these days as there was so many coming out so quickly.

 

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henriquesalvador

Hi @GregS,

 

Readings of SNMP values are made every 30 minutes by the Agent. Which is sufficient for most cases, it's on our backlog a way to customize this frequency.

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