On 05/28/2012 05:38 AM, Bruno Jesus wrote:
On Sun, May 27, 2012 at 6:47 PM, Jean-Michel Pouré - GOOZE
<[email protected]> wrote:
My question is about USB connection/disconnection. The USB hubs have a
separate AC/DC. If I connect a hub with 7 readers, in some cases, it may
connect and then disconnect. The light on the hub blink and then are
disabled ... one by one, maybe one every second.
I have worked in a project where we needed the max possible amount of
readers to build a SAM server. We ended up with 104 readers + 20 hubs
(looks like the usb device limit is 127). The main problem was that
the motherboard was not able to provide enough power for all the
readers so we elected 4 usb hubs that were powered externally. Each of
these main hubs are connected to a different motherboard usb port. On
each main hub we connected 4 other hubs. So we ended up with 16
secondary hubs with 6 or 7 readers each. Some cheap brands of hubs
bought from dealextreme could not handle that amount of readers,
specially some fake 7 port hubs which are in fact 2 hubs of 4 ports
interconnected. You should try other brands of hubs if you have
problems with power and disconnection. You can always look at dmesg to
see if the readers are getting recognized/disconnected.
Hi Bruno,
I've been working a bit on a project / appliance that uses many smart
cards, usually between 10-50, sometimes more.
At the moment, we have a "reasonably stable" solution, yet USB
disconnect issues happen from time to time, even with hubs and power
sources we consider reliable.
Can you provide an indication of brands and models that you found
rock-solid?
One customer is also experiencing some trouble potentially because of
the cable lenght (3mt USB cabling just to the first hub, another one
follows in chain but with a shorter distance); do you think this could
be part of the problem? Have you had any experience/issue involving
cable lenght?
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