Experiences with external UMTS dongle

Werner Almesberger werner at openmoko.org
Sat Jul 4 15:44:23 CEST 2009

Timo Juhani Lindfors wrote:
>> My assumption is, that it takes far more than 2.5W, since the USB dongle 
> How about measuring that? Just read the current_now file in /sys.

Telephony can have very high current peaks, in the order of 2 A.
They are only short, i.e., the size of some transmit time slots,
so the average current is much lower, but if a design doesn't
adequately buffer those peaks, there will be problems.

Problems should get worse in areas with poor or no reception.

Monitoring rapidly-changing current is difficult, but if current
peaks cause a voltage drop, that could be detected by measuring
USB VBUS with an oscilloscope.

- Werner

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