Raspberry Pi System Temperature

Introduction

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.

Requirements and prerequisites

• OpenHAB has been installed on Raspberry Pi
• The Exec binding has been installed
• RRD4J persistence has been installed
• User openhab is member of the video group

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

Solution

This solution was developed for a Raspberry Pi 2 model B running Raspbian) and an apt-get installation.

The temperatures for both CPU and GPU can be read through terminal commands:

$ cat /sys/class/thermal/thermal_zone0/temp
46540
$ /opt/vc/bin/vcgencmd measure_temp
temp=47.1'C

This means the output can be captured using the Exec binding.

However. The CPU temperature is returned as millidegrees Celsius. (I'm not sure if another OS localization returns Fahrenheit). The GPU temperature has some surrounding text for readability. Both need some transformations to get the values into OpenHAB properly.

The CPU temperature is computed through a Javascript transformation. The GPU temperature is captured through a Regex transformation.

This example gets the CPU temperature 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

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

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

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 to rrd4j.persist file:

System_Temperature_Chart* : strategy = everyChange, everyMinute, restoreOnStartup

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

• OpenHAB Community Thread