cputemp2mqtt

Periodically report CPU temperature average to a MQTT broker.

This is a very simple shell script that I use to report my Raspberry Pi's CPU temperature to my Home Assistant instance.

It takes CPU temperature samples at a given rate and reports the average to a MQTT broker every n-th sample. This should help smooth out random spikes, because it allows you to sample the CPU temperature more frequently while keeping a relatively long period between reports.

Usage

The script is started by systemd in normal use. However, it can also be started manually:

$ ./cputemp2mqtt -h
Usage: ./cputemp2mqtt [-v] {-f config_file |
                            {SAMPLING_PERIOD REPORT_PERIOD
                             [args_for_mosquitto_pub]}
                           }

-v : verbose mode -- echo debug messages to stderr
-f config_file : read configuration from file
SAMPLING_PERIOD : how often (in seconds) should CPU temperature be read
REPORT_PERIOD : report average temperature every n-th sample
args_for_mosquitto_pub (examples):
    -h hostname
    -p port-number
    -t message-topic
    -u username
    -P password
    ... (see man mosquitto_pub)
    Avoid using the -u and -P arguments because it leaks secrets through the
    process name. Use ~/.config/mosquitto_pub instead.

Script running with verbose mode on:

$ cputemp2mqtt -v 1 5 -t rpi/cpu_temperature
Verbose mode is on
SAMPLING_PERIOD: 1
REPORT_PERIOD: 5
MOSQUITTO_PARAMS: -t rpi/cpu_temperature
New sample: 45'C; array:  457
New sample: 46'C; array:  457 462
New sample: 46'C; array:  457 462 462
New sample: 46'C; array:  457 462 462 467
New sample: 44'C; array:  457 462 462 467 447
New average: 45.9
New sample: 45'C; array:  457
New sample: 44'C; array:  457 447
New sample: 45'C; array:  457 447 457
New sample: 45'C; array:  457 447 457 452
New sample: 46'C; array:  457 447 457 452 462
New average: 45.5
...

The verbose mode output is only helpful for debugging purposes.

The New sample: xx'C message only shows the integer part of the sample, but it is in fact a decimal number. This can be seen in the array, where the sample multiplied by 10 is stored. This could use some improvement...

Installation

# install the script, it's config file and systemd unit file
sudo make install

# edit /etc/cputemp2mqtt
# edit /etc/systemd/system/cputemp2mqtt.service

# reload systemd units
sudo systemctl daemon-reload

# enable and start the systemd service
sudo systemctl enable --now cputemp2mqtt.service

Configuration

A configuration file can be specified using the -f flag. This file is sourced during the script's startup. See example configuration file cputemp2mqtt.conf.

Systemd

You can use the systemd unit file cputemp2mqtt.service to make this start automatically. The default configuration file is /etc/cputemp2mqtt.