A digital picture frame with weather forecast
Updating Photos
The simplest way to update the Raspberry Pi might be to wait for some special trigger file to be generated. In this case, you would just list the files in a directory on Dropbox, and when the trigger file exists, you would transfer the files.
Although I might use this method to coordinate a file transfer at work, this solution doesn't exactly scream user friendly. A different method would be to copy over all the files periodically to the Raspberry Pi. In this case, the synchronization is just a matter of removing all existing photos, gathering a list of all images on Dropbox, iterating through that list, and copying over each file. In the future, I might revise the synchronization mechanism, but for now, I will do this once a week.
The first step is to gather up a list of files to be copied over and then to iterate through that list. A rather cute way of doing this is to use both head
and tail
to get a specific entry from the list:
NAME=`head -${IDX} $WORKFILE | tail -1`
Downloading the file from Dropbox is then just a matter of running dbxcli
with the name of the current file to retrieve.
Selecting and Displaying a Picture
Displaying a picture is as easy as running the feh
program with the name of the file to be displayed over the desktop. The entire goal of the picture frame is to allow for dynamic updating of photos, but even keeping that in consideration, the photos will remain fairly static most of the time; therefore, I maintain the current list of files to display, which is generated each time the files are copied from Dropbox.
Displaying all photographs is just a matter of looping through the list of existing files. Each photo should be displayed for at least a few minutes. I decided that the script shouldn't run continuously; instead, from the list of pictures, it should choose the current image, display it, and exit. The script, then, is run by a crontab file every few minutes. For this to work, the script will need to maintain its state between runs.
The pickpicture
method in Listing 2 retrieves the current item in the list to be displayed, advances the index, and then displays the current picture.
Listing 2
Display Bash Code
01 pickpicture() 02 { 03 IDXFILE=$PICDIR/index.dat 04 cd $PICDIR 05 06 IDX=`cat $IDXFILE` 07 CNT=`cat $PICLIST | wc -l` 08 NAME=`head -$IDX $PICLIST | tail -1` 09 10 IDX=$(($IDX + 1)) 11 12 if [ $IDX -gt $CNT ] 13 then 14 echo 1 > $IDXFILE 15 else 16 echo $IDX > $IDXFILE 17 fi 18 19 showpicture $NAME 20 21 cd $INSTDIR 22 }
Downloading Weather Data
Retrieving the weather for a given city is quite easy. The OpenWeather site does the authentication once at the beginning and gives you a time-unlimited key, so you only need to pass the key in with each call:
CMD="http://api.openweathermap.org/data/2.5/weather?id=${CITYID}&appid=${APPID}&units=metric" curl -s $CMD > $TODAY
The script simply makes a call to the OpenWeather URL with the appropriate parameters, and you receive a JSON object in return from the curl
utility. The returned weather structure is not overly complicated: Simply select each field of interest.
Extracting the values was straightforward except for sunrise and sunset, because these values are stored as a Unix UTC value. The good news is that this can easily be converted to a more user-friendly value with the date
command:
# parse out data from data file sunset=`cat $TODAY | jq -r '.sys' |jq -r '.sunset'` sunset=`date --date=@$sunset +'%H:%M:%S'`
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Direct Download
Read full article as PDF:
Price $2.95
News
-
KaOS 2022.06 Now Available With KDE Plasma 5.25
The newest iteration of KaOS Linux not only adds the latest KDE Plasma desktop but sets LibreOffice as the default.
-
Manjaro 21.3.0 Is Now Available
Manjaro “Ruah” has been released and includes the latest Calamares installer, GNOME 42, and much more.
-
SpiralLinux is a New Linux Distribution Focused on Simplicity
A new Linux distribution, from the creator of GeckoLinux, is a Debian-based operating system with a focus on simplicity and ease of use.
-
HP Dev One Linux Laptop is Now Available for Pre-Order
The System76/HP collaboration Dev One laptop, geared toward developers, is now available for pre-order.
-
NixOS 22.5 Is Now Available
The latest release of NixOS with a much-improved package manager and a user-friendly graphical installer.
-
System76 Teams up with HP to Create the Dev One Laptop
HP and System76 have come together to develop a new laptop, powered by Pop!_OS and aimed toward developers.
-
Titan Linux is a New KDE Linux Based on Debian Stable
Titan Linux is a new Debian-based Linux distribution that features the KDE Plasma desktop with a focus on usability and performance.
-
Danielle Foré Has an Update for elementary OS 7
Now that Ubuntu 22.04 has been released, the team behind elementary OS is preparing for the upcoming 7.0 release.
-
Linux New Media Launches Open Source JobHub
New job website focuses on connecting technical and non-technical professionals with organizations in open source.
-
Ubuntu Cinnamon 22.04 Now Available
Ubuntu Cinnamon 22.04 has been released with all the additions from upstream as well as other features and improvements.