[clug] Raspberry Pi WLAN issues

Rodney rodneyp at iinet.net.au
Tue May 27 17:01:59 MDT 2014

+1 to the comments re current draw on RPi.

It can be exacerbated by the vintage of the Pi.  Early 256M RAM examples had 
very limited current supplied internally to the USB ports - I could not get 
mine to work at all with some USB-Ethernet adapters directly connected.  

OTOH, mine works rock solid as a firewall/router by having all USB items, 
including the extra USB-Ethernet adapters hanging off a 2.5A powered USB hub - 
which also powers the Pi itself via uUSB cable.

It's worth plugging each USB device that will be used with an RPi into another 
PC and issuing:

lsusb - v

then reading the max Power for each device and drawing up a mA budget for the 

The Pi uses a chip which hangs the internal Ethernet port off internal USB bus 
too - effectively uses a USB I/O bus.  Aggregate I/O will be limited to 480 
Mb/s and that could give the impression of drop-outs.


 On Tue, 27 May 2014 22:43:01 Jessica Smith wrote:
> Hey all,
> I work in a college environment, where people are doing interesting things
> with RPis to engage students. We have a fairly typical enterprise-type
> network environment, with all the joys and tears pertaining thereto…
> We have an RPi that is giving one of the IT teachers some grief, and I took
> a quick look at it today. He's trying to get it connecting via wifi using a
> USB wifi dongle, and it seems to be… somewhat flaky. Using the wifi
> config util (GUI), sometimes nearby networks are discovered and displayed,
> sometimes not. When attempting to connect to the desired WLAN (802.1x, all
> settings correct), it will appear to connect, then drop. Occasionally, the
> wifi config util seems to lose the WLAN0 interface altogether, and only a
> reboot restores (wlan0 down/up doesn't fix).
> I'm thinking flaky adapter, and am arranging to swap out the adapter, but
> it's possible/probable I'm missing something obvious. The RPi is running
> Raspbian.
> Does this sound like a flaky adapter to y'all, or is there a known
> flakiness in support for USB wifi adapters in Raspbian that's unknown to
> me? (I don't know what chipset the dongle is running, but can find out.) Is
> it likely an issue with the RPi not having correct datetime set? (I didn't
> check this today but will tomorrow.) If a time problem, how do people
> usually manage this without access to an NTP server until after connecting…?
> Any other troubleshooting suggestions much appreciated.
> Cheers,
> Jessica

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