article

|

(This post is also contributed to the openHAB wiki)

The Systeminfo Binding enables you to read system information through Sigar. The system information provided through this library can be extended with some additional important features. For example, reading system temperatures for your Raspberry Pi.

CPU temperature

The CPU temperature can be read with a terminal command:

$ cat /sys/class/thermal/thermal_zone0/temp
46540

This output can be captured using the Exec binding. The value returned represents millidegrees Celsius. (I’m not sure if another OS localization returns Fahrenheit). So the actual needed CPU temperature is computed through a Javascript transformation.

GPU temperature

The GPU temperature can be read with a terminal command:

$ /opt/vc/bin/vcgencmd measure_temp
temp=47.1'C

This output can also be captured using the Exec binding. The value returned is surrounded by text for readability that can be removed through a Regex transformation.

This example gets both temperatures in degrees Celsius every 60 seconds and persistently stores them for presenting in a graph. It assumes that all items containing system information (potentially including those for the Systeminfo Binding are in a systems.items file (any other items file will do).

Example configuration

Assumptions

Add openhab user to video group

The user openhab needs to be member of the video group to be able to run the vcgencmd command. Otherwise you will see a VCHI initialization failed error message.

Group memberships are only updated after a reboot.

$ sudo usermod -a -G video openhab
$ sudo reboot now

Create javascript transformation

Create a milli.js file (in transform folder) with this content:

(function(i){ return i / 1000; })(input)

Add new items

Add to system.items file:

// System temperatures
Group  System_Temperature_Chart (System, Charts)
Number System_Temperature_Chart_Period "Periode" (System)
Number System_Temperature_CPU "Temperature CPU [%.1f °C]" <temperature> (System_Temperature_Chart) { exec="<[cat /sys/class/thermal/thermal_zone0/temp:60000:JS(milli.js)]" }
Number System_Temperature_GPU "Temperature GPU [%.1f °C]" <temperature> (System_Temperature_Chart) { exec="<[/opt/vc/bin/vcgencmd measure_temp:60000:REGEX(temp=(.*?)'C)]" }

Add persistence for items

Add to rrd4j.persist file:

System_Temperature_Chart* : strategy = everyChange, everyMinute, restoreOnStartup

Update sitemap

Add to default.sitemap file:

Text item=System_Temperature_CPU label="Temperature [%.1f °C]" {
    Frame {
        Text item=System_Temperature_CPU
        Text item=System_Temperature_GPU
    }
    Frame {
        Switch item=System_Temperature_Chart_Period mappings=[0="1h", 1="4h", 2="8h", 3="12h", 4="24h"]
        Chart  item=System_Temperature_Chart period=h   refresh=60000 visibility=[System_Temperature_Chart_Period==0, System_Temperature_Chart_Period=="Uninitialized"]
        Chart  item=System_Temperature_Chart period=4h  refresh=60000 visibility=[System_Temperature_Chart_Period==1]
        Chart  item=System_Temperature_Chart period=8h  refresh=60000 visibility=[System_Temperature_Chart_Period==2]
        Chart  item=System_Temperature_Chart period=12h refresh=60000 visibility=[System_Temperature_Chart_Period==3]
        Chart  item=System_Temperature_Chart period=D   refresh=60000 visibility=[System_Temperature_Chart_Period==4]
    }
}

Sources

This solution was developed for a [Raspberry Pi 2 model B]({% post_url 2015-04-03-my-first-raspberry-pi %}) running Raspbian) and an apt-get installation of openHAB.