A while ago I bought a version of Kyosho Blizzard, which features the new iReceiver which lets you control standard servos and ESC’s with your tablet or mobile phone. There’s also a camera fixed to Blizzard’s fuselage for streaming video. I didn’t have high expectations about the video performance but for the video the range is really poor. For controlling, the range is what you would expect for wi-fi device, about 50 m. The application however stops streaming the video as soon as it detects even a slight packet loss, which generally happens after 20 m. The thought arose, that since mobile networks are nearly ubiquitous, how about tunneling the traffic via 3g connection?
After completing the home electricity meter hack I looked for options to have small display hanging on the wall, which would show useful information. I had previously bought Samsung SPF-87H photo frame which can be used as an external monitor. The frame connects to computer with usb and the picture is updated by simply sending it in jpeg format. Few caveats are that display needs to be first initialized to “mini monitor”-mode and the picture size must match exactly to the display resolution (800×480 in case of SPF-87H). I chose Beagleboard as the embedded computer to keep the power usage low. BB has one usb and one usb-otg port. I’m planning to change the Beagleboard to Raspberry Pi, when they became available since this doesn’t use all the resources provided by the Beagleboard.
Even that the Beagleboard has only one true usb-port, I did not need to add the usb-hub to setup, since the usb-otg port can also be used as host. The display connects to otg-port, since it has it’s own power supply (otg-port can’t supply power) and the regular usb port is used for wlan adapter.
The photo frame has desk stand but no hole to hang it on the wall. This was fixed by using hot glue to attach a piece of wire to the backside to act as hanger. I learned later that I should have made a loop to the both ends of the wire to increase gluing surface. The frame dropped to floor after couple of days, resulting small crack to bezel and a dent to floor. Fortunately the display continued working.
The finished display looks quite nice. The Beagleboard and the power supply are hidden on top of cupboard and the display cables are hidden inside cable duct.
The software “WallDisplay” running on the Beagleboard is written in C++ and uses Qt. The software simply reads Sqlite database, which contains a list of urls and time, how long the url is displayed on the screen. The web pages are loaded to QWebPage and its contents are exported as jpeg file, which in turn is pushed to the display. Qt’s webkit implementation has too many ties to the user interface for it to be used as command line QtCore-application. Since the program does not have to actually show anything on a real monitor nor accept user input, I’m using xvfb to simulate X-server. In future I’m planning to add web interface to make it easier to manage the displayed pages.
Currently the display is rotating following pages:
- Electricity usage
- Weather forecast
- Calendar, exported from iCal
- Irc log from the channel we used with my friends
- Last picture from the security camera
The sources are available at: https://gitorious.org/home-automation/walldisplay
You also need to install software for controlling the display from here: https://github.com/Gekkio/samsung-photo-frame-ctrl
See rc.local file for an example how to run the application. Path to database and path to frame-ctrl program must be given as arguments. The database creation command is in the readme.txt file.