Quote:
Originally Posted by gwynevans
The current - the USB voltage is specifed to be 5.0V (which is near enough to 5.2V) but it's the amount of current that varies. I think they adhere to the letter of the specs, whereas most devices may not - I'm not 100% about that, but this is the only reason I can see that explains why it works with real controllers what would support the USB 'handshaking' but not with PSUs that would just supply power...
See http://www.usbmadesimple.co.uk/ums_2.htm ("Device Powering") and http://www.beyondlogic.org/usbnutshe...htm#Electrical , particulalry "Suspend Current", which I wonder might be involved... |
Gwynevans, this is EXACTLY what I was hoping for!
I read through the first URL's pages, and a lot of it did penetrate my thick skull; fortunately most of the really confusing stuff was for data transfer rather than power supply. The second one, and as you say, the "suspend Current" section might very well hold the key to what I'm trying to do. If I'm correct, then what I need to find is a 3rd party USB device that meets the criteria, gets the proper Configuration Descriptor, and it all
'should' work!
What really amazes me is that there is SOOOOO much going on inside a little block of plastic with some bits of wire, and yet it cost's less than $10!
Thanks again for pointing me in another good direction!
(I realize all of this may pan out to absolutely nothing, but it beats watching "Days of Our Lives" or "Eastenders!"
)
Stitchawl