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32-bit processor? They seem to be
everywhere but the work actually
being done by them can be minimal.
A 16-bit or 8-bit microcontroller
may be more efficient in some
applications. It does depend on
what code is running and the
efficiency of the compiler. If there
is a Bluetooth or Internet interface,
then more memory may be required
and a 16-bit or 32-bit processor
should be used. A TCP/IP stack with
a web server also requires a 32-bit
processor. Creative software writing
can minimize the resources needed
and therefore minimize power
consumption.
Wider data width processors
consume more power in a number
of ways. Accessing 32-bit RAM and
Flash memory is more power hungry
than accessing 16-bit memory.
Also, leakage current increases with
wider memory. That points towards
keeping memory size to a minimum
both by efficient code structuring
and writing, and also not choosing
a processor with massive amounts
of excess memory.
RF power
If there is a RF wireless interface,
e.g. Bluetooth Smart, consider the
transmitting distance. Not only are
there power savings by transmitting
with lower power, the receiver
sections can have adjustable
sensitivity and will take less power
when sensitivity is set lower. For
example, the Nordic Semiconductor
nRF52832 has a high receiver
sensitivity mode using 10.9mA but
normal sensitivity only takes 6.1mA.
Custom ICs
The ultimate lower power solution
might be a full custom IC design
with only the required circuitry.
Circuitry that never drives off-chip
consumes a lot less power. However,
it is the slowest and most expensive
way of developing a product. It is
also probably why a Frederique
Constant Smartwatch battery lasts
2 to 3 years and a Fitbit Flex lasts 3
to 5 days.
Summary
There are a lot of aspects to
consider when designing a low
power system. It can be a good
idea to create a spreadsheet
with all the parts of the system
listed with current consumption,
required duty cycles, voltages and
total power consumed. Then for
each design scenario calculate the
projected power consumption. The
only way to find out some of the
information needed is to actually
build a prototype and test it.
New-Tech Magazine Europe l 25