Hardware Reference
In-Depth Information
to post an angry
but it works for me
rebuttal online. Things that shouldn't work some-
times do.
The touchscreen used in this hack (more about that in
“Touchscreen” on page
280
)
comes with a power cable to connect directly to a 12 V receptacle, so you won't need
to worry about it. However, because you need a powered USB hub to prevent the
Raspberry Pi from using too much power (and simply turning off or behaving errati-
cally), you will need to get an
inverter
.
In this context, an inverter is a device that takes the 12 V DC power coming from the
“cigarette lighter” and changes it to an AC power outlet (the amount of wattage pro-
vided varies by the unit). These inverters vary in quality (and functionality), but be-
cause you need to plug only one thing into it, 200 watts should be enough.
We have successfully used a number of 300-watt inverters on the market. If you want
to spend the money, you can get a pure sine-wave inverter that provides an exact
replica of AC household power with two ground fault protected outlets and will likely
work for
years
reliably and silently. This comes with a cost, though, as they run about
$175.
Instead, you can get a modified sine-wave inverter for $20-30. These do not work as
reliably, but they should work to power a USB hub. They're also a lot louder and hotter,
usually with fans running all the time.
Storage for Your Movies
The next thing you're going to need is a place to put your digital video files. While you
could put a few of these onto the SD card running the Raspberry Pi, that space will fill
up quickly (and these files are usually quite large).
You'll also need to factor in the fact that you're installing this in a moving car. That
rules out a traditional portable hard drive, because it has moving parts and is not
usually very tolerant of a lot of bumps.
Instead, you're going to use a solid state drive (SSD). The technologies behind SSDs
have been around since the 1950s, but since then, they've gotten much bigger (in
capacity), much smaller (in size), and much cheaper (in cost). SSDs are basically big
blocks of memory without any mechanical moving parts. This makes them very fast,
but more importantly for this hack, they work perfectly through every bump and
bounce of your car.
You can connect an SSD to the Raspberry Pi over USB. Purchase a drive that is de-
signed to be external, or buy an internal SSD and put it in an external USB chassis. At
this point, the majority of these USB chassis units are USB 3.0, due to the high speed
(up to 5 Gbit/s at half duplex, twice that at full duplex). This is fine, but the Raspberry
Pi can only communicate across its USB bus at USB 2.0 speeds (up to 480 Mbit/s),
