Once upon a time I had a particularly rubbish car. actually the car was great fun to drive, and never really broke down it was as basic as you could get.
the stereo was also basic, but it had an audio jack socket on the front. and I had something called an Mstation, this is a large hard disk MPs player, with an LCD screen that shows the tracks playing etc.
Then I got a new car, there was no where to mount my Mstation, but I had a cd changer (rather than just a player)
And then that wasn't enough.
so I got a PureDAB digital radio, but the reception was rubbish.
But what it did have was a audio input jack socket.
I decided that rather than re-use my Mstation (which I'd still have to mount and find a way to get to the controls cleanly, I wanted something invisible.
That is when I decided that my car should have a computer in it.
Now this isn't the standard car-puter build, I've already made it reasonably clear that I don't want to cut holes in my dashboard (else I'd just use the Mstation).
and I want this to be as hidden as possible.
and that's when it hit me.
I'd use a computer and use my phone as the control unit.
I also knew I would never want to take the computer or hard disk out of the car, I'd want to be able to pull up to my house and access the computer via my standard home network
The computer had to be something that would not loose power.
I had an old laptop that was not being put to use so I decided that I would use this.
being a laptop it came with it's own power supply that could keep it running even when the car was off, (when I parked up outside my house)
For simplicity, because it offers an "out the box" solution I decided that I would use Itunes, with the itunes remote application on my phone being used to alter the volume and to skip tracks, where the phone could sit in a regular phone holder as I drove.
The computer had a relatively small hard drive, so storage will be a small USB powered external hard drive
The iphone does not like non-infrastructure networks, and besides, I want the laptop to connect to my home network, so it can't be trying to be an infrastructure network
To accomplish this, the wireless network of the latptop would be set to autheticate on my home network. now whenever I drive near to my house the computer will recognise the network and connect to it.
The wired connection on the computer will connect to a wireless access point which will server a localised network (called pugnet as my car is a peugeot) this is the network that my iphone will connect to, allowing itunes remote to connect to the itunes software for control.
The power for the laptop will be provided by a shop bought in car laptop power supply. the power for the WAP (9v) will be provided from the cars 12volt electronics and be regulated with a 2a LM7809 voltage regulator.
The front squab of my passenger seat lifts up to reveal a little storage compartment, the computer will sit under the seat in the front of the car, hidden from passing eyes,
All the fiddly electronics bits are build into a wooden box that sits in the bottom of the compartment,
the laptop sits on top.
How it all works.
I leave my house in the morning, and get in my car.
when I turn my car on, the laptop receives power and ideally boots up (no worries if it doesn't). additionally the wireless access point turns on.
as I drive down the road my iphone looses connectivity to my home network, but finds the car network pugnet and authenticates on this network.
if the computer has not started I use a free application on the iphone called NetAwake to send a packet to the computer requesting that it wakes up (wake on LAN is enabled on this laptop)
the computer turns on and boots, Itunes is in the startup folder and so automatically starts.
When I start the itunes remote application it searches the network for itunes servers, and finds the laptop.
I press play, the laptop plays songs (from the USB hard drive) through the laptops external audio connection, which connects to mu PureDAB highway radio, which transmits via FM to my stereo, and plays through all the speakers.
When I get home...
the laptop discovers my home network and connects
I turn off the car, this immediately kills the power to the access point (which turns off) and kills power to the laptop. -the laptop remains on powered by battery power.
I go inside.
start my regular computer, where I can use VNC to connect to the car laptop and update the itunes library with songs that I can just drag and drop wirelessly into my car!
until the laptop battery runs out. at which point windows knows that it's low on battery power and gracefully shuts down the machine.