The Raspberry Pi Transit Appliance

For the last several months I’ve been beta-testing the Raspberry Pi as the processor for our Transit Appliance technology stack, and it’s a very good fit. We use the 512MB “Model B” ($35). By the time we add a case, power supply, SD card and WiFi adapter, the build cost is in the neighborhood of $60.

The image file for our Transit Appliance build of the Raspbian OS is here (1.8GB). It’s our version 1.4 – we’re tracking releases by overall functionality, not per platform. This includes a number of changes to make our loader javascript more robust. Unlike the Atom platform where we use the Iceweasel version of Firefox, this platform uses Chrome (actually Chromium) as the web browser.

Here are excellent instructions for how to burn the image file to an SD card (2GB should work, but we generally use a 4GB card as they are more available) for a variety of OS’es.

A significant difference from the Atom platform is the way WiFi is configured. On the Atom (Webconverger) platform, the WiFi connection parameters are edited in a config file on the SD card. With Raspberry Pi there is a WiFi client app with a nice GUI. To access it, connect a keyboard and mouse (more on that below) and take the browser out of full-screen mode (Alt-F11), and you’ll find the WiFi app on the desktop. After getting your WiFi connection set up, kill the browser entirely (Alt-F4) and it will restart automatically in full-screen mode again.

Connecting a keyboard and mouse is a bit tricky, as there are only two USB ports on the Pi and one of them will already be occuppied with the WiFi adapter. One approach is to connected a powered USB hub. But I’ve found it easier to connect a keyboard that has a built in pointing device. I’ve found the wireless¬†IOGEAR GKM681R very convenient.

One more way the Raspberry Pi version differs: I’ve found that our appliance applications run anywhere from 800 to 1500 hours before they crash (my guess is due to browser memory leaks). Rather than force someone to manually reboot the units after a crash (and if the crash results in a frozen but reasonable-looking display, it might take a while to notice!), on the Raspberry Pi distribution, I’ve added a cron job that reboots the OS overnight (3AM). My hope is that this should result in pretty much entirely unattended operation.

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