I need to make notes on this stuff anyway, it might as well be here.
I’ve gotten some complaints that my posts are too long and too broad in scope, and that this makes it difficult to find information. I think the complaints are valid, so I’m trying to break up subjects further than I usually do.
Yesterday I spent some time experimenting with the Raspberry Pi Zero W. Other than needing a more reliable SD “imaging” tool than “dd”, it went well.
It is possible, indeed routine, to power the Raspberry Pi Zero (and the Raspberry Pi Zero W) through the USB data jack, rather than the USB power jack. This seems to be not only intentional but part of the USB OTG specification and concept. The Raspberry Pi Zero and Raspberry Pi Zero W are intended to be usable as USB “devices” as well as USB “hosts”. In other words, the entire Linux machine can act as a USB peripheral as well as being the “master”, or “computer”. This has some really interesting potential that I don’t think has been adequately written about yet. I’m not just thinking about using the Raspberry Pi Zero and Raspberry Pi Zero W as mass data storage, but as computers connected to other computers as peripherals, in effect a tiny, portable network of computers all maintainable from one but also capable of acting autonomously… in effect, tiny computers as hardware sub-systems for a main computer.
This means that if a USB cable is supplying power and data both, as is typical when plugged into powered hubs and USB jacks on other computers, only one USB cable/connection is required, there’s no reason to split out the power into a separate connection.
It was possible to “backpower” the first generation of Raspberry Pis this way, but there were problems with it (as I recall there was discussion of current limitations and even possible damage). I’m under the impression that this was regarded as a mistake, and it was “corrected” in subsequent versions, which didn’t allow it.
Together with the extremely low power requirements of the Raspberry Pi Zero and Raspberry Pi Zero W, this can have a liberating effect on its use. If other USB-equipped devices are present, unlike the other Raspberry Pi computers it doesn’t have to be tethered to its own power supply.
– Robert the Wombat