Gets meteogram from yr, and crops it with imagemagick. End goal is to hang a selfupdating pictureframe on the wall.
Updating the meteogram
can be done by running the script:
This is also where the image is cropped and resized to fit the desired screen size. If 320*480 doesn't work for you, you'll have to play around a bit.
It would be the responsibility of the user to update the meteogram image periodically by running the refreshMeteogram.sh command in an appropriate location. Here's a crontab that runs it every 15 minutes:
*/15 * * * * /home/pi/meteogrammer/refreshMeteogram.sh > /home/pi/meteogrammer/cron.log
Viewing the meteogram
feh --reload 10 --fullscreen meteogram.png
Will launch a viewer that auto reloads the image every 10 seconds.. which is probably a totally overkill interval..
showMeteogram.sh contains the command i use to display the meteogram on my 3.5inch RPI LCD:
fbi -T 2 -d /dev/fb1 -noverbose -t 300 /home/pi/meteogrammer/*.png -cachemem 0
Even though you ask fbi nicely to not cache anything, it still will, unless the slideshow consists of at least 3 images. This is worked around by creating 2 symlinks to the meteogram.png as detailed by Jamie Jackson (who also gives more details about the above fbi command) here
I found a 3.5 inch waveshare RaspberryPi LCD on aliexpress, but the backlight was tremendously on at all times, so the meteogram pictureframe was blinding at night.
I decided to look into modifying the LCD module to control the backlight. I found this on the raspberryPi forums which looked promising but left out a couple of details.
The brightness.py script reads a value from a light sensitive resistor (by measuring the charge time of a 1µF capacitor) and sets a corresponding duty cycle for the PWM output
Here's a look at the back of the LCD module. Notice the lm 1117 which generates the 3.3V which used to be hardwired to the LCD backlight anode, the middle pin is now connected to the emittor of the PNP transistor:
Here's where i cut the trace to the LCD backlight common anode (pin 1 on the flex connector on the LCD module) and soldered a wire to the collector of the PNP transistor (you can't actually see the cut. It's directly underneath the blue wire) :
Here's a closeup of the LCD module PCB under the display, pin numbers for the connector match those of the RaspberryPi, how convenient:
Schematic of the modifications
Here's a hand drawn schematic of the modifications i've made:
The base resistor can be calculated from the hFE of your chosen transistor and the backlight current which i have measured to be ~100mA.
I used the tried and tested flexbox postscript file to start a design which i then adapted with holes that match a raspberryPi and the display module. I ended up with the design shown here, which is available in meteoPI_box.svg