Although this thread is quite old, I'd like to step in and describe what I am currently trying to build with my RasPi. Maybe this could help others as well as solve the problems I'm facing at the moment...
I want to use the RasPi as an audio-only car entertainment system. Since we're using the Logitech Squeezebox Server software and several hardware clients
at home, I decided to install the Squeezeplug image
. Playback can be controlled with a fairly intuitive iPhone/iPad-App (actually not the free one from Logitech but the 3rd party app iPeng), so the RasPi won't need a display. To connect the RasPi with the iOS device a WLAN connection is needed. Since a stand-alone WLAN network in the car the iPhone is connected to would prevent the iPhone from accessing the internet, some sort of 3G connectivity is needed. After playing around a little bit with a UMTS USB stick hooked up with the RasPi (with embarrassing results), I put together the following setup:
1. Internet connectivity is provided by a fairly cheap 3G wireless router. As I already had a UMTS stick I choose the TP-Link TL-MR3020
for around 30 Euro. The RasPi is connected via ethernet while the iPhone uses the wireless LAN. An alternative would be to buy a mobile router with built-in 3G (like the Huawei E5
) and a WLAN stick for the RasPi.
2. The music comes from a 2,5" USB HDD. An idea for the future is to wirelessly synchronize the mobile music collection with the collection on the file server at home when the car is parked within reach of the home WLAN.
3. The Squeezebox Server software (now called "Logitech Media Center") as well as a software squeezebox client are installed on the RasPi.
4. Everything is powered over a USB hub (which gets power from a 5A 12V/5V DC/DC converter). The hub in turn gets its USB uplink from the RasPi. (Yes, this looks strange but since the micro USB port on the RasPi is only for power, it works...)
On a first test, the playback started to cause problems after an hour. At the moment I don't know if this is a CPU issue or some other sort of problem caused by overheating - it was a very hot day. I decided to use the playback function of the iPeng app (streaming the audio to the iPhone) and it worked for the rest of the five hour trip.
The main problem with this setup is that there currently is no way to automatically power down the RasPi. I think there are three possibilities to solve this:
1. Setup a read-only system and hook up the whole thing to the switched 12V power supply. Problem: No way to save playlist even if the engine is turned off for just a minute. Also, synchronizing with the home collection get's somehow tricky.
2. Use one of the GPIO pins to (manually) give the RasPi the signal to power down and have a seperate on/off switch. Problem: You can't really tell if the RasPi is powered down correctly and are sitting around in the car waiting for the right moment to use the off-switch...
3. Building some sort of power-off delay switch which tells the RasPi (via GPIO) to shutdown, maybe even with the possibility to delay the shutdown for some time (e.g. when you are making a small break on a tour) or manually overriding the shutdown. I could also live with an off button (NOT a hardware off switch!) that triggers the shutdown and final poweroff. Problem: I do not have that much experience with this sort of electronics.
@kaos: From what I understood you already build a circuit that does something like what I described above. Would you mind posting the schematics?
Sorry for this long post, but maybe it helps anyone of us.