First things first, get yourself a powered USB hub
and a DC-DC converter
that can provide the DC volts the hub needs. Some adapters you can regulate with a dial, so if your hub needs 5V, you just turn the dial to 5V and Bob's your uncle. Cheap to get. Then hook everything up to that USB hub, including your pi. This way your pi will boot whenever the car is started. Keep in mind that you do not want to overload the DC-DC converter by exceeding its advised maximum amperage. You can
exceed, and you won't do any critical damage if you do, it's just not a very great idea.
Now, this means that every time you start your car, you'll have to wait for the pi to boot. You can get around that by powering your DC-DC adapter directly from your battery. Do not be tempted to do this though, because if you keep your carputer running with the ignition off, your battery will be depleted faster than you think. Probably a few days or a week max. Again you can go down this road if you want to, but it's not a great idea.
Equipment wise you'll also need an OBD-II cable
to interface with your car's actual onboard computer. There are wireless bluetooth adapters on the market which make for smooth-sailing compatibility but, since these use power, it's hard (impossible?) to find one which doesn't drain your car battery over time; even with the ignition off. Hence I'd advise a USB OBD-II cable. Every car made since 1996 is equipped with an OBD-II interface, although in the early years the connector used to vary somewhat among manufacturers.
What you'll also want to get is a GPS receiver
. There are many posts on the forum on this topic and the receivers are all over ebay, but long story short: get one that receives the most possible contemporary satellites all at once. Use gpsd to read out the positioning data.
There is even a funky little tool called obdgpslogger
which logs both OBD-II info and GPS data into an SQL database (or whatever it'll be) which is awesome for recording trips or datamining.
Another really cool thing to get is a mobile internet adapter like a 3G USB stick
, or a wireless access point and a Wi-Fi dongle. That way your pi will have an internet connection.
And when you have THAT set up, install a MUD client
so you can come play some Discworld MUD while you drive. See you there!
Linux Dev and oldskool elite