becker wrote:I did consider using usb for power. The OSSC draws somewhere between 700 and 800mA. The idea was the usb cable is universal and people plug into a regional phone charger to the wall outlet. My worry is that usb cables or hosts like a TV might only be rated for 500mA. Maybe someone who knows more can say if this is a valid fear.
Spec wise, USB 2.0 is only required to provide 500mA, but I believe by standard the port is rated to handle up to 5A load. In any event, the vast majority of phones charge over a regular USB 2.0 cable at 1A to 2A. You're safe to draw 700 to 800 mA (assuming 5V) if the supply supports it, and if they plug it into something that doesn't support it (like maybe their TV won't do more than 500mA), that shouldn't be the end of the world, they'll just need to use a different charger.
As for the actual mechanism for drawing more than 500mA, I'm not sure: there are a large number of battery charging an power delivery specs for USB, some of which involve data for negotiation, some of which simply involve resistors for identifying capability, and some devices probably just go ahead and try to draw the power and see what happens.
It's worth pointing out that the Raspberry Pi is USB powered, with a recommendation to use a 2A power supply, so I really don't see why the OSSC drawing less than an amp over USB would be a problem.