Anelok: the power struggle
werner at almesberger.net
Thu Apr 9 09:54:04 UTC 2015
> - Parallel CR2032
Parallel 2032 would improve things, but they'd still not be able
to cover the maxima specified for uSD cards.
Also, please don't forget that the 2032 with holder occupies about
a third of the inner volume of the current Anelok design. So adding
another one would grow the case by 30% and turn it into a long
Serial 2032 (with a down-converter) in a stacked holder would add
about 3-4 mm of depth, which is again an increase of 35-45%, and
brings the peak depth in the ballpark of an AAA. Also, the
down-converter would either have to run all the time or the MCU
would need a way to switch it supply between converter and one cell.
> - Rechargeable coin cell http://www.digikey
Max. Discharge Current: Continuous: 10 mA, Pulse 20 mA. Cell
voltage about 300 mV below a CR2032. Nominal capacity 100 mA.
> Changing the microsd storage by flash storage don't improve the situation,
> because they also typically eat 10-15ma when writing :S
10-15 mA would be quite alright if a write doesn't take forever. The
problem with uSD is that the specified maximum current high and that
operations can take a lot of time.
Interestingly, the parameter for reads and writes are not too
dissimilar. Not sure if this means that a read can also trigger a
write (e.g., to refresh or replace a failing block).
In case reads are fine and writes are a problem, there would also be
the possibility of caching writes (which should be rare and move
little data anyway) in the Flash of the MCU (maximum page erase time
113 ms, maximum current 4 mA) if on battery and to copy it to the
card only when on USB power.
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