One of my thoughts for using the Raspberry Pi is to monitor ambient temperature in my house and send me warnings if it is too low. This would be helpful when away from home in the winter and there is an issue with the heat that I might need to know about fairly quickly.
Eventually I might consider building in a weather station capability into the Raspberry Pi by using both an indoor temperature, humidity and barometric sensor and an outdoor temperature and humidity sensor. So with that in mind I also want to make some simple graphs of data every hour or so. Something that can be just saved into a text file and requires no extra graphing code on the client or the server.
CPU Temperature Experiment
I started out by experimenting with taking reading of the CPU temperature of the Raspberry Pi in order to get a little practice with some live data while I was awaiting the arrival of a Bosch BME280 ambient temp., humidity and barometric pressure sensor.
sSMTP
I plan on using sSMTP to send me warnings, such as when my ambient temperature falls below a critical value. I have already worked up some code to monitor the CPU temperature and email me if it goes out of a specific range, to get a bit of practice with coding this into a script. Plus it was a good way to try out sSMTP. sSMTP will be covered in more detail in a separate post.
Snippet of script that sends email if the upper and lower CPU temp limits are exceeded
The temperature read by the cat /sys/class/thermal/thermal_zone0/temp is in milliCelsius, so using cut on it will grab whole degree values. The rest of the code is pretty straightforward. The variables minimum and maximum are setup to be the appropriate values in whole degrees Celsius. mailaddr is exactly what it sounds like. What is nice is that it just gives you a very simple method of sending a basic email warning when the temperatures get out of bounds.
# Read the temp and cut it to grab leftmost 2 characters, integer Temp temp="`cat /sys/class/thermal/thermal_zone0/temp | cut -c1-2`" #echo $temp # Mail if about or below the limits if (( $temp > $maximum )); then #echo "above" echo "Rasp Pi CPU Temp = $temp. " | mail -s "Rasp Pi HIGH CPU Temp > $maximum" $mailaddr elif (( $temp < $minimum )); then #echo "below" echo "Rasp Pi CPU Temp = $temp. " | mail -s "Rasp Pi LOW CPU Temp < $minimum" $mailaddr fi
Simple Graphical Temperature Logging
To just monitor the CPU temperature on a hourly basis and have a simple graphical representation of it I had to do some digging online.
I dug around the web and found a bit of Perl code to make a simple ASCII graph of the temperatures that I was measuring for the CPU. I wanted to be able to simply post to the web a running capture of temperatures, grabbed hourly by using CRON. I did not want to have to rely on graphing tools either on the Raspberry Pi or the client computer to interpret data. I spent a while searching for something simple and this was about as easy as it can get. I found a one line, long line! Method for creating a simple graph using Perl. I looked around a lot on line and wanted to avoid anything that would have to be installed on either the Raspberry Pi or the client machine to be able to plot data. So after a long search this piece of Perl code is about as simple as it gets and will plot and ASCII based graph across one line each time it executes.
The key variables in the code are min, max and w. The variable w controls the width of the plot in characters that it will be allowed to reach when the input value is at max. The variables min and max control the minimum and maximum input values expected and scale the graph accordingly. PLOTTABLE_FILE is the path/filename of the file that the output will be sent to.
PLOTTABLE_FILE=/var/www/tmp/cputemp-milli-celsius.txt
Perl Code Snippet
The code resides in a script in the /etc/cron.hourly directory and produces a file that is readable via the web, with a new entry every hour. The filename is cputemp, not the lack of a .sh extension. This is important when you create scripts that will reside in the “CRON” folders. It also has to be made executable by using sudo chmod +x filename.
(cat /sys/class/thermal/thermal_zone0/temp ) | perl -ne '$min=20000; $max=65000; $w=79; use POSIX; $d=ceil(log($max)/log(10)); $w-=$d; $v=$_<$min?0:$_>$max?$max:$_; $s=$w*$v/($max-$min); $bar=join("", ("*")x$s); $bar=~s/.$/|/ if $v==$max; print sprintf("%${d}d ",$_)."$bar\n";' >> $PLOTTABLE_FILE
Sample Output
Below of a capture of a few lines of output from the text file that is generated by the Perl code. It does not look as clean as it would by looking at the text file. So I have a capture of that here…. cputemp-milli-celsius
42236 ********************************************************************* 41160 ******************************************************************* 41160 ******************************************************************* 41160 ******************************************************************* 40084 ***************************************************************** 41160 ******************************************************************* 42774 ********************************************************************** 44388 ************************************************************************ 45464 ************************************************************************** 45464 ************************************************************************** 46002 ***************************************************************************
Alternate Method to Read CPU Temperture for the Raspberry Pi
There is another way to read the CPU in a more human readable form. Executing the line below…
/opt/vc/bin/vcgencmd measure_temp
…will show a result like this…
temp=45.5'C
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