Re: An 80 port USB Board

> D> > > An 80 port USB Board:

> > >
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> > > > > Unfortunately it looks like it is just for power, so I wonder if ther=
e
> > is a call for such a device. > > > > > Was interesting enough to point out, but who could really use it? > > > A device manufacturer who wanted to charge units before shipping?

....

Add to that that the USB port is slowly becoming (to the consumer) a > de-facto +5v power socket, with USB socketed +5v plugpacks, Car > cigarette lighter inverters sometimes have a couple of +5v USB sockets > on them as well as the 240v socket. Phone charger cables are available > that plug to USB to charge. >=20 > In time, the USB socket will likely become a universal +5v supply > source (without data lines) for just about every consumer gadget, just > as the car cigarette lighter socket has become a standard 12v power > socket for anything and everything.

Already is the case, so nobody has enough USB sockets.

Wait for the PC/laptop that has 80 sockets for all the devices to be=20 plugged in. =20

The 500ma limit of a normal USB port might be a problem in some > applications, but this is more than enough for most gadgets out there, > and definitely enough for charging batteries used in most portable > devices.

When no enumeration has taken place about 90mA, you can only get 500mA AFTER a data exchange to do enumeration.

--=20 Paul Carpenter | snipped-for-privacy@pcserviceselectronics.co.uk PC Services Timing Diagram Font GNU H8 - compiler & Renesas H8/H8S/H8 Tiny For those web sites you hate

Reply to
Paul Carpenter
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That's the theory, but in practice most machines don't bother and just give

500mA. Every machine I've tried has. And powered USB hubs are supposed to give 500mA without question.

Dave.

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Reply to
David L. Jones

ere

I have read about that too, but in practice, I have had no problems with powering "dumb" devices (ie: ones that only connect to the power pins and dont utilise the data pins) from USB ports drawing currents substantially in excess of 90ma. (tested only up to about 400ma)

I have only tried this on various ASUS motherboards though, not laptops.

In reality, one of the real limiting factors can be that the +5v wire in the various USB cables, as well as the wire between the USB sockets in the front of cases and the cables to the motherboard, is not of a sufficient thickness to avoid voltage drops when the device at the end is drawing currents at the upper end of the limit.

We actually had a USB lead in the workshop with the +5v and ground wires cut and brought out of the cable at both ends, and a thicker wire (0.5mm sq) running on the outside of the cable to the other end to avoid this problem when testing some devices.

Some Portable USB hard drives (laptop type) were notorious for this problem, but I have noticed that modern USB cables seem to be a lot better in this regard - possibly for the very reason that these portable drives have become more popular in recent years, whereas I cant remember seeing these around when USB was first introduced.

I doubt that these drives would have had much of a data transfer rate in the early days until USB 2 speeds came along.

Reply to
kreed

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