Power management for car audio pi
I would like to build a headless hires music player for the car with enough hard drive space for all my music. Let's say 1tb. At this stage, I’m not particularly concerned about other aspects often associated with a car pc such as satnav, bluetooth etc, but that may come later. I would like the player to function as much as possible like an 'appliance' and not like a PC. The main road block has been having to shutdown the pc before the engine is switched off then booting up next time i get in the car and select my music/playlist each time. Very cumbersome. I want a simple automated play/pause when stopping/starting the car without the PC draining the car battery in between uses.
So here are my thoughts/plans. Please feel free to poke holes in them. I’d rather iron out as many issues in the planning stage as possible.
Not particularly important at this time, but I’m considering options such as Volumio, Openelec/Kodi and JRiver Media Center. I can try various options once I have the hardware set up.
Raspberry Pi 2 Model B
Hifiberry or similar DAC connected to the line in/AUX on my existing head unit. Still looking at various DAC options.
1tb laptop hdd (already have a spare) connected via usb to Pi. May need to go through a powered hub.
Existing iPod touch with appropriate app for chosen software. Will connect to Pi via usb wifi dongle set up as access point on the Pi.
Power Supply and Management:
Here’s where things get complicated. Ideally, what I would like is some sort of power management module that would send a sleep signal to the pi when ‘Acc’ power is turned off. The pi would still be powered by the car battery, but in sleep mode would (hopefully)use a sufficiently small amount of power that car battery would not drain in between drives. Up to about 48hrs should be sufficient for my purposes. When ‘Acc’ power is restored, the module would send a wake signal. A very happy side effect of this set up is that this would produce the pause/play behaviour that I’m looking for.
I have done some searching and found the following 2 modules that may be able to achieve this:
I would love to here from anyone who has experience with them or can recommend any possible alternatives.
Obviously the power of the wifi dongle and the hdd need to be managed also. I assume they would sleep along with the pi if connected directly via usb. I’m a little concerned about lag time for them to wake and be available when the pi wakes and resumes playing. The hdd may be able to be managed by increasing the music buffer size in software. It may take some time for wifi dongle to come back on-line and the iPod touch to reconnect and then the app to connect to the player. This may not be fatal, but perhaps an annoyance.
So, please let me know if you think this will all work as I hope or if I should go about it another way. I have considered using a rechargeable battery pack. That may still be an option.
Thanks in advance.