Hardware Reference
In-Depth Information
• Mounting frame
• Battery box
• 180 watt DC-to-AC inverter (for printer)
• Lightning arrestor and earthing system
The hardware required for the RACHEL server is identical to the client/student con-
figuration, except that it requires a larger SD card—32 GB for only RACHEL-Pi or 64
GB if KA-Lite is included. Because 64 GB cards are not well-suited to the purpose, only
cards rated UHS-1 will work for that scenario. In addition, a router facilitates commu-
nication between student clients and the servers. The UHS-1 class 64 GB cards that
have been tested and known to work with the Pi include:
• Kingston SD10G3/64GB UHS-I Elite
• Lexar Platinum II SDXC UHS-I Card
• SanDisk Ultra® SDXC™ UHS-I
Set Up the Raspberry Pi
Powering Potential uses Raspbian for the student Raspberry Pis. Emmanuel Acker-
man, technical adviser at Powering Potential, offers configuration tips on the
World-
Possible forums
under the handle mannyack.
Most importantly, he notes that the default sound configuration is “auto,” which
means that if you connect the monitor through the composite video port, the sound
will be directed through the audio jack, and if you connect the monitor through the
HDMI port, the audio will be directed to the HDMI audio. The monitor they use is an
HDMI monitor that doesn't support audio. To tell Raspbian to use the headphones,
you should be able to run:
$ sudo amixer cset numid=3 1
Mannyack recommends doing this manually through
/var/lib/alsa/asound.state
in
a text editor instead, followed by pulling the power to force a shutdown.
The Raspberry Pi's GPU can be used for video decoding, including high-definition
video. Raspbian includes a video player called omxplayer, which uses the GPU for
processing. Powering Potential has adapted the
media-berry package
that reroutes
HTML5 video playback in Midori (the default Raspberry Pi web browser) for omxplayer
to work with RACHEL videos.
The lab is powered by solar powers installed on the roof of the computer lab in a
conventional arrangement (panels and batteries). Power cabling brings the 12 V power
produced by the sun from the batteries to the computers. A 12-volt-to-5-volt stepdown
converter brings that down to usable power for the Raspberry Pis. The monitors,