Silicon Labs' MCU scores design win in fitness energy tracker

October 29, 2013 // By Graham Prophet
Misfit Wearables selects the EFM32 Leopard Gecko to maximise battery life in its personal physical activity monitor design

Silicon Labs has announced that Misfit Wearables, a designer and manufacturer of wearable computing products, has chosen its EFM32 Leopard Gecko 32-bit microcontroller (MCU) as the energy-friendly controller for the Misfit Shine physical activity monitor. The Gecko MCU communicates with the Shine’s 3-axis accelerometer, drives user interface LEDs and hosts a Wicentric Bluetooth Low Energy software stack, enabling connectivity with the Shine App running on Apple iOS devices such as iPhones and iPads, with highest energy efficiency.

Like all portable, battery-powered devices, the Shine wearable activity monitor requires extreme energy efficiency to maximise battery life. Instead of using a rechargeable battery, the Shine runs on a single, user-replaceable CR2032 lithium-ion watch battery for four months. Instead of having to recharge the device every few days, the end user simply wears the Shine and monitors his or her fitness activity daily without interruption until it is time to replace the battery.

The Misfit design team chose the MCU for energy efficiency across all energy modes, enabling long battery life coupled with optimal processing performance and a high level of integration in a small-footprint package. The Leopard Gecko MCU’s low-energy sensor interface (LESENSE) and peripheral reflex system (PRS) were attractive features for Misfit’s ultra-low-energy budget. The LESENSE interface autonomously collects and processes sensor data even when the MCU is in deep-sleep mode, enabling the MCU to remain in a low-energy mode for a long time while tracking sensor status and events. The PRS monitors complex system-level events and allows different MCU peripherals to communicate autonomously while keeping the CPU in an energy-saving sleep mode as long as possible to reduce overall system power consumption.

According to Sonny Vu, CEO and co-founder of Misfit Wearables. “We needed a 32-bit embedded controller that could handle sophisticated algorithms, process and transmit lots of data, interact seamlessly with a motion-sensing accelerometer and fit within an insanely small form factor... Silicon Labs’ Simplicity Studio development tools accelerated