In Car Media Player

[SteveMilner]

Hi.

I have a Model B Pi, running RASPBMC with a UPiS UPS board attached and a small wifi router plugged in to the Ethernet (powered externally).

My project is an in car Media Player.

The Pi and the UPS board are performing exactly as expected:
Ignition off, wait for 20s delay and shutdown the Pi.
Power on Pi Boots up and starts the media server (minidlna)

However the problem lies with the external hard drive, which is connected through a powered USB hub and a DC-DC convertor to provide the 5v power supply to the hub.

When I switch off the ignition the power drops to the Pi, The USB Hub and the wifi. (But that's not a problem.)

At this point the UPiS powers the Pi, the Pi then seems to power the Hub, the External Hard Drive and at the very least the LED on the DC-DC convertor.

It's all too much for the poor Pi and it shuts off immediately, which wasn't quite what I intended.

I'm considering my options, but I think they are limited.

I could use a sealed lead acid battery to connect to the switched car power and also to the DC-DC convertor, but without knowing the idle power requirements of the hub and hard drive I've no idea if this is even sensible.

If anyone could recommend an ultra low power external hard disk then that might be an option.

if anyone knows how to limit the USB maximum current supply to the USB standard (140ma?) then that might help.

Has anyone solved this problem themselves, if so, could you pass on your knowledge.

Regards,
Steve

[Jessie]

Do you want the hub to pull power from the pi? If not put some diodes on the feed lines comming from the pi to the hub.

If you want the hub to shut off at the same time as the pi the solution becomes more complex.

[SteveMilner]

I don't want the pi to power the hub.

Not sure how diodes will help.

I tried cutting the red power cable within the USB connector to the Hub, but all that happened is that the Pi didn't recognise that I had plugged a USB in, a diode I'm guessing would have a similar effect, but I could be wrong.

If you could explain how you wire the diodes into the cable perhaps I could give it a go.

Regards,
Stephen

[SteveMilner]

If I could find a USB hub that was only self powered and not both self and USB powered then that might solve the problem.

Trouble is most hubs these days are both self and USB powered and it's not always obvious which ones are which.

If anyone knows of a hub that is only self (externally powered) and does not try to draw power from the USB from the Pi please let me know.

Regards,
Steve