The Xiaomi Mijia smart door lock employs eight AA batteries, and provides up to 18 months of battery life before replacement in standard operation, thanks in part to the ultra low power characteristics of the Nordic SoC. The nRF52840 SoC has been engineered to minimize power consumption with a fully-automatic power management system that reduces power consumption by up to 80 percent compared with the nRF51 Series.
Nordic’s nRF52840 multiprotocol SoC is Nordic’s most advanced ultra low power wireless solution. The SoC supports complex Bluetooth LE and other low-power wireless applications that were previously not possible with a single-chip solution. The SoC combines a 64MHz, 32-bit Arm® Cortex® M4F processor with a 2.4GHz multiprotocol radio (supporting Bluetooth 5, ANT™, Thread, Zigbee, IEEE 802.15.4, and proprietary 2.4GHz RF protocol software) with 1MB Flash memory and 256kB RAM. A new radio architecture with on-chip PA provides features -95dBm RX sensitivity (at 1Mbps Bluetooth LE), a maximum output power of 8dBm, and a total link budget of 103dBm. The chip supports all the features of Bluetooth 5 (including 4x the range or 2x the raw data bandwidth (2Mbps)) compared with Bluetooth 4.2.
The SoC is supplied with Nordic’s S140 SoftDevice, a Bluetooth 5-certified software protocol stack for building long range and high data Bluetooth LE applications. The S140 SoftDevice offers concurrent Central, Peripheral, Broadcaster, and Observer Bluetooth LE roles, and supports high throughput and long range modes as well as advertising extensions. OpenThread and Zigbee stacks are available through Nordic’s nRF5 SDK for Thread and Zigbee.
“Although other wireless protocols were an option, Bluetooth LE was more suitable as it is not only faster but also provides a better experience and satisfies our need for stability,” says Tao Liu, Lumi Product Manager. “We selected the nRF52840 SoC both for its range and ultra low energy consumption. The maximum output power of 8dBm provides much greater connection range, while the low power consumption extends the battery life of the door lock.
“From a software point of view, the performance of the Nordic SoftDevice, and a widely used API were the features we valued most. When we require it, Nordic can also quickly provide professional technical support.”