Monday, February 4, 2013

Jumbo Digital Picture Frame

What do you do with a spare flat panel monitor?  If you are a Raspberry Pi hobbyist, you turn it into a jumbo size digital picture frame.  Photography is another of my hobbies and this is a great way to display my work.

Hardware Part 1 - Modify the Monitor Power Supply

This section requires some knowledge of power supplies and delicate soldering skills.  This step is totally optional and can be skipped.  I didn't want a second wire hanging from the picture frame for the Raspberry Pi power supply, so I tapped 5V off of the monitor's power supply.  You can power the Pi normally.  If you are really lucky you will have a monitor with a built in USB hub and you can power it from there.

I completely disassembled the monitor and located 5V and ground on the back side of the power supply where one of the connectors attached.  The wires in the lower right of this image show the power lines that I attached.

I shouldn't need to say this, but: DANGER.  Make sure the power supply is unplugged when you work on it.  Mains power can kill you!

Hardware Part 2 - The Control Panel

The monitor outputs 5V even if it is turned off, because it isn't really off - just in standby.  I added a power switch and LED as well as a push button to signal the Pi to shut down.  A simple script will monitor the pushpbutton and execute a halt when it is pressed.

If you only want to install the shutdown button, just connect it to a GPIO pin and to ground.  The pinouts that I used are shown here.  Don't be concerned about the inconsistency in the GPIO pin numbers.  This is explained below and is due to differences in the pin numbering used by the Raspberry Pi developers, the native pin numbers on the BCM chip, and the WiringPi library.

Hardware Part 3 -Build a case and put it all together

I used the plastic from the case to an old backup tape.  These are more flexible and a lot less brittle than most plastic CD cases.  I was able to use scissors to cut the plastic to fit the curved shape on the rear of the monitor.  Machine screws hold the case together tightly enough to keep the Raspberry Pi in place.  It is mounted so that the SD card extends a little bit below the monitor.  I would have liked to have it all hidden, but there wasn't room and this does make it easier to remove and insert the SD card.

Both the case and the control panel are held in place with Velcro   This allows me to peel the case loose so that I can plug a network cable in if needed.  Tie wraps are used to hold the HDMI cable and power cable neatly in place.  It is a very tight fit.

A added a short length of rope for hanging which is attached to the top two VESA mounting screws.  My frame is 21 inches and is quite a bit heavier than a typical painting, so I wanted something stronger than a typical picture hanger on the wall.   My work of art wouldn't be happy crashing to the floor.  I was very lucky and found a stud in the wall exactly where I wanted to mount the frame.  If you have to use drywall anchors, then I recommend using two about four inches apart and make the rope long enough to go over both.  If your walls are stucco, then I wish you luck.

System Preparation

Windows only recognizes the first partition on removable media and I wanted a large FAT partition to put the pictures on when the SD card is plugged in to my Windows laptop.  That means I had to use the /boot partition for this purpose.

  1. Load Raspbian as usual. Shut down the Pi and remove the sdcard.
  2. Install "Minitool Partition Wizard Home Edition" on a windows system with an sdcard slot.
  3. Run the partition wizard and move the second partition (the system partition) all the way to the end of the disk space.  You could shrink the partition first but I didn't bother.
  4. Expand the first partition to fill the remaining space.
  5. Put the SD card back into the Pi, boot up, and log in.
  6. Update the apt database using:  sudo apt-get update
  7. Install the Linux Frame Buffer Interface using:  sudo apt-get install fbi
  8. Create a directory to hold the pictures that the frame will display:  sudo mkdir /boot/PICTURES 
  9. Create a new user named "slideshow" which is a member of the "video" group:  sudo adduser slideshow --ingroup video
  10. Change the inittab file to automatically log on the slideshow user:  sudo nano /etc/inittab   Find the line that begins 1:2345:respawn:/sbin/getty --noclear 38400 tty1  Comment out that line by placing a # in front of it and then add this line:  1:2345:respawn:/bin/login -f slideshow tty1 </dev/tty1 >/dev/tty1 2>&1
  11. Create a script to run the slideshow:  sudo nano /boot/  which includes this one line: fbi -noverbose -m 1920x1080 -t 10 /boot/PICTURES/*.jpg   
  12. Some notes about the fbi command line:  The -m option specifies the resolution to use on the monitor.  This may need to be changed to display better for the monitor that you use.  The mode specified must be in the /etc/fb.modes  file.  I had to add the mode I needed, which is shown below.  The -t 10 option causes the program to run a slideshow with a 10 second period for each picture.  The -a option causes the program to automatically resize the images to fit the screen.  When I first tried this I was using 10 mega pixel images (about 3800 pixels across) and the Pi was taking 8-10 seconds to perform the resize.  To prevent this I removed the -a option and used FastStone Image Resizer to resize all the pictures for my slideshow to fit into a 1920x1080 screen.  You can find that utility here:
  13. Make the script executable:  sudo chmod 775 /boot/
  14. Edit the bash login script for the slideshow user:  sudo nano ~slideshow/.bashrc  and add this line to the end:   /boot/
  15. Once all of the above has been done, you can reboot and the system will automatically run the slideshow.  You can stop it by pressing Control-C on the keyboard.
  16. Of course, you have to put some pictures in the pictures directory.  You can do this many ways, but I re-partitioned the sdcard so that I could plug it into my laptop and copy pictures directly to the sdcard.  The fbi command will support formats other than JPG, so don't feel that you are limited to that format.  You do need to realize that Linux is case sensitive with file names, so be sure to rename them all consistently. 

Here is the block that I added to the /etc/fb.modes file:

mode "1920x1080"
    geometry 1920 1080 1920 1080 32
    timings 0 0 0 0 0 0 0
    accel true
    rgba 8/16,8/8,8/0,0/0

The default fb.modes file did not include a 1920x1080 resolution so I had to find this example.  Fortunately it  works fine with my monitor.  More information about the fb.modes file can be found here:

Trigger Shutdown Script 

The drawing above shows the shutdown switch connected to GPIO-1.  I normally refer to the GPIO pins using the WiringPi numbering scheme.  However, I am not using WiringPi for this project.  We will access the GPIO pin via the /proc filesystem.  WiringPi GPIO-1 is GPIO-18 to the system.

Create a script to monitor the pin and perform a shutdown: sudo nano /etc/ini.d/   
The contents of the script is this:


# monitor GPIO pin 18 (wiringPi pin 1) for shutdown signal

# export GPIO pin 18 and set to input with pull-up
echo "18" > /sys/class/gpio/export
echo "in" > /sys/class/gpio/gpio18/direction
echo "high" > /sys/class/gpio/gpio18/direction

# wait for pin to go low
while [ true ]
if [ "$(cat /sys/class/gpio/gpio18/value)" == '0' ]
echo "SHUT DOWN NOW *****"
        halt &
        exit 1
sleep 1

First, the GPIO pin is configured for input with a pull-up resistor enabled.  Then the scripts loops once a second and checks if the pin is pulled low from the push button being pressed.  If it is, then it executes the halt command and exits.

This script must be run at startup.  The easiest way to accomplish this is to add it to the end of the local startup script:  sudo nano /etc/rc.local
Add this line at the end of the file:
/etc/ini.d/ &
The & at the end of the line makes the command run in the background.  Without it, the local.rc script would not exit and the system would hang on startup.

All Completed: