| by wmack

Plotting the temperature of your PI

If you are living in Arizona and you have a PI outside, you might want to keep an eye on its temperature. It might get a bit hot, and you might need to know how far you can push the PI before it starts acting funny…
So here is a recipe for doing this.

If you are living in Arizona and you have a PI outside, you might want to keep an eye on its temperature. It might get a bit hot, and you might need to know how far you can push the PI before it starts acting funny…
So here is a recipe for doing this.

Assumptions:

I’m assuming that

  • you will use two systems: The PI, and a regular system, which I will refer to as the “PC.”
  • Both are on the same network, and you can ssh into the pi, and you know the IP address of the PI, or it has a name you can somehow resolve into an IP address.
  • you use the account “pi” on the pi.
  • you have the plot utilities package installed

Shell script on the pi:

  • copy the text below into a file “thermal_recording.sh” 
    ---------------------------------------
#!/bin/bash
while [ 0 ] ; do 
(echo -n $(date +"%s ") " " ;cat /sys/class/thermal/thermal_zone0/temp)  >> temp_recordings ; sleep 60 ; done
----------------------------------------
  • run command
    chmod 755 thermal_recording.sh

  • To have script start on power-up run command
    crontab -e

    and add this line:
    @reboot /home/pi/thermal_recording.sh

Set up ssh login without password

  • on the PC, if you do not already have a file ~/.ssh/id_rsa.pub, run the command
    ssh-keygen
    You can give empty responses to all prompts.
  • scp the file ~/.ssh/id_rsa.pub to the pi
  • on the pi, append the content of the transferred file to file .ssh/authorized_keys
    cat ~/id_rsa.pub >> .ssh/authorized_keys
  • verify that you can ssh into the pi without the need of a password

If you want to publish your work to a web site, set up an appropriate folder there.

Set up the PC side of things

  • create a folder ~/bin
  • create the file ~/bin/temp_plot.sh with the content below. Adjust the variables DIR, PI_IP, and (if you desire so) PUBLISH_URL 
    ---------------------------------------------------
#!/bin/bash
set -x

#local variables: 
#folder in which the work happens and the url to which to publish
DIR=temp_plot_files
PI_IP=xxx.xxx.xxx.xxx
#leave this blank if you don't want to publish
PUBLISH_URL="user@hostname:html_folder"

#prep function. creates folder where the processing happens and
#puts in the html template
function prep
{
cd
mkdir -p ${DIR}
cd ${DIR}
cat>abc.template<<EOF
<html>
<head>
<script type="text/JavaScript">
<!--
function AutoRefresh( t ) {
	setTimeout("location.reload(true);", t);
}
//   -->
</script>
</head>
<body onload="AutoRefresh(100000)">
<b>replacing</b><hr>
<img src=temp.png></img>
</body>
</html>

EOF
}

#iter function. Does the work periodically
function iter 
{
rm -f `find . -type f | grep -v html | grep -v png|grep -v template`
scp "pi@${PI_IP}:temp_recordings" .

if [ $? -ne 0 ] ; then
  exit 
fi

gnuplot <<EOF
set terminal png
set output 'temp.png'
set grid back
show grid
set xtic 3600*24
set xdata time
set timefmt "%s"
set key outside bottom
set format x "%m/%d"
plot "temp_recordings" using (\$1-7*3600):(\$2/1000) smooth cspline with lines lw 4 title 'temp_centigrade'
EOF

cat abc.template | sed -e "s/replacing/$(date)/" > temp.html

#publish if a url has been defined
if [ "x${PUBLISH_URL}" != "x" ] ; then
  scp *.html *.png ${PUBLISH_URL}/.
fi
}

prep 
while [ 0 ] ; do iter ; sleep 600 ; done
---------------------------------------------------------
  • run
    chmod 755 ~/bin/temp_plot.sh
  • on the PC, run the command
    crontab -e
    and add the following line
    @reboot ~/bin/temp_plot.sh

At this point you can reboot the PI and the PC, and the scripts should start running

if you are lucky, you should see a working example here.

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