New-Tech Europe Magazine | Feb 2017

Power Efficient Design for Wearable Electronics

Mark Patrick, Mouser Electronics

advice will look at larger savings, and some on small. After all multiple small savings, soon add up to an overall larger one. Sleep Mode Sleep mode is a natural first step for any designer looking for a low power usage design. This will be especially important for wearable designs as they usually won’t be powered totally down. Most wearables will take periodic sensor readings and either store the reading till it can be sent, or send the reading immediately. It makes sense to put the design into sleep mode between active periods. The device can be brought out of sleep mode by an interrupt, or by a physical input, such as a button push. How often the device is awake will depend on the application. Even within the application, sleep times can vary

quite considerably. Dynamic sleep intervals are often used to allow the device to judge how often it needs to make measurements. In the case of a fitness device, it can wake and check for movement. If there is movement, it will intelligently narrow the time between measurements. In contrast, if there is a lack of movement, it can extend the time till the next measurement, prolonging battery life. Communications between ICs The communications protocol between devices can be important for energy saving. I2C uses pull-up resistors, which dissipate energy. SPI doesn’t have pull-up resistors, so may prove a better choice. Another way that energy can be lost in communications is pin capacitance. To minimize this figure, reduce the

There are not many people who doubt that one of the next big growth areas in the electronics industry will be wearables. Some predictions claim that the market for wearables could increase to $10bn by 2020. Reaching that target will depend on the user experience of the wearable, and one of the main attributes that users use to judge portable products is battery life. Squeezing every last drop of available life from the batteries is vital for designers of wearable devices. Users are looking for batter life measured in months, rather than hours. To meet these exacting targets requires the designer to look into every aspect of the design, from the start up time of clocks, to the MOSFET switching times. This article will look at some of the methods that designers can use to save every joule of energy possible. Some

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