New-Tech Europe Magazine | Feb 2017

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.

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

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