Nordic’s Bluetooth SoC Shines in OxiWear Ear-worn Pulse Oximeter

March 21, 2023 by Jake Hertz

OxiWear’s new pulse-oximeter solution highlights the potential use cases for Nordic’s nRF52840.

While wearables offer unprecedented health monitoring capabilities, developers face significant design challenge with these small devices. Designers must integrate advanced functionality, including sensing, data processing, and wireless communication, into a small, low-power, and lightweight wearable device.

To do this, wearable makers rely on highly-integrated SoCs that incorporate disparate functionality onto a single piece of silicon. One such SoC is Nordic’s nRF52840, which was recently used in OxiWear’s new, ear-worn pulse oximeter device.


Nordic’s nRF52840

Nordic’s nRF52840. Image courtesy of Nordic Semiconductor


In this article, we’ll look at the nRF52840 as well as OxiWear’s new product to see how a highly integrated SoC can help enable lightweight and low-power wearables.


The nRF52840: A Multiprotocol Bluetooth SoC

Nordic Semiconductor's nRF52840 is a multiprotocol Bluetooth SoC designed specifically to enable low-power, connected devices. The nRF52840 supports a number of wireless protocols, including Bluetooth 5.3, Thread, and Zigbee. For Bluetooth, the SoC comes equipped with a multiprotocol radio, which supports long-range +8dBm transmit power, a -95 dBm sensitivity, and data rates up to 2 Mbps.


Product comparison of the nRF52840's protocol support

Product comparison of the nRF52840's protocol support. Image courtesy of Nordic Semiconductor


From a compute perspective, the SoC is built around a 32-bit, Arm Cortex-M4 processor that is supported by 1 MB of flash and 256 kB of RAM. This is complemented by a 64 MHz floating point unit, a 12-bit ADC, and other features such as an on-chip DC-DC buck converter as well as NFC-A and USB 2.0 support.

Overall, the device is meant to balance low-power operation and performance, allowing for operation down to 1.7 V supply voltages and sleep modes as low as 0.4 µA at 3.3 V.


Ear-worn Pulse Oximeter

As a testament to the nRF52840’s viability, this week Nordic announced that the SoC is being used to power a new, ear-worn pulse oximeter device from OxiWear.

The device, which is designed to continuously monitor oxygen levels in real-time, aims to support the more than 10% of the global population at risk of hypoxia, a potentially life-threatening disease that can cause tissues in the human body to not receive enough oxygen. Hypoxia is caused by environmental factors, high altitude living, chronic medical conditions, and other factors.


OxiWear’s pulse oximeter device

OxiWear’s pulse oximeter device. Image courtesy of OxiWear


The device is worn on the ear and features an integrated optical sensor for photoplethysmography, a non-invasive technology that uses a light source and a photodetector to measure the volumetric variations of blood circulation, and an accelerometer for motion detection and cancellation. The device is powered by Nordic’s nRF52840 SoC, which serves as the primary processor for running OxiWear's complex DSP algorithms and performing housekeeping duties like firmware updates, power management, and storing historical data to Flash.

The Bluetooth LE connectivity enabled by the nRF52840 SoC allows real-time health data to be relayed wirelessly from the device to the user’s smartphone, where an accompanying app displays the blood oxygen and heart rate information. The app also collects environmental data that may affect oxygen intake and contact emergy contacts in the event of a hypoxic event.

Thanks to the low-power nature of the nRF52840, the OxiWear device can be powered by a rechargeable Li-ion coin cell battery and can operate for up to 18 hours even when worn continuously.