Proximity Monitoring Wearable Combines Bluetooth LE and Ultrasound to Track Social Distancing

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Nordic Semiconductor announces that M2MD Technologies, an Atlanta, GA-based IoT software solutions company, has selected Nordic’s nRF52840 Bluetooth 5.2/Bluetooth Low Energy (Bluetooth LE) advanced multiprotocol System-on-Chip (SoC) to power the ‘Coolpad Bubble’ proximity monitoring solution. The Coolpad Bubble has been co-developed with its hardware manufacturer, Coolpad, a global consumer electronics company, to help companies create a safer environment for their employees during the Covid-19 pandemic. 

The Coolpad Bubble is designed to assist with the enforcement of social distancing guidelines in indoor/outdoor workplaces and industrial environments including factories and warehouses. The compact (51 by 51 by 16mm form factor) and durable (IP54-rated) wearable, which attaches to the user’s shoulder via a strap, features four TDK ultrasonic transceivers which detect proximity to neighboring devices. Users receive visual, audio, and haptic vibration alerts when another device is within a 1.8m perimeter. 

Bluetooth LE and ultrasound precision

The Coolpad Bubble uses a combination of Nordic SoC-enabled Bluetooth LE and ultrasound to determine the distance between devices to a precision of 1 to 3cm—the highest accuracy on the market, according to the developers—with no additional infrastructure or beacons required. Each device autonomously periodically transmits its unique identifier for receiving devices to monitor and then measure the difference in ‘Time of Flight’ (ToF) between the Bluetooth LE packet and an ultrasonic audio packet. The time difference is proportional to the distance between transmitter and receiver.Nordic has the best availability, depth, and accuracy of technical documentation online for all developers
Chuck Link, M2MD Technologies

The sensor and algorithm data processing capability for the Coolpad Bubble is powered by the Nordic nRF52840 SoC’s 64MHz, 32-bit Arm Cortex M4 processor with floating point unit (FPU). The Arm Cortex M4 processor is combined with a 2.4GHz multiprotocol radio (supporting Bluetooth 5.2, ANT™, Thread, Zigbee, IEEE 802.15.4, and proprietary 2.4GHz RF protocol software) and a generous 1MB Flash and 256kB RAM memory allocation. 

Real-time proximity monitoring

In addition to ‘real-time’ proximity monitoring and alerts for wearers, the Bubble platform provides comprehensive data on contact interactions and contact tracing history for tracking adherence to social distancing guidelines through the Cloud-based ‘Coolpad Bubble Dashboard’. The advanced contact tracing is compliant with the most recent CDC guidelines (October 2020). Secure recording of non-personal data and intrusion alerts including device ID, distance, timestamp, and event duration enables detailed reporting and analytics. This data is currently relayed from the device to the Cloud via Wi-Fi connectivity. In future the solution could also be used to access more anonymous positioning data about workers for AI-enabled workflow optimization, hazardous situation monitoring, and various other uses cases. 

The Bubble device uses a 900mAh Li-Po battery to provide battery life of multiple days or at least eight hours of continuous proximity detection before recharge, using a multi-unit charging bank, thanks in part to the ultra-low power characteristics of the Nordic SoC. The nRF52840 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. 

The nRF52840 provides full Bluetooth 5 support including 2x on-air raw data bandwidth (2Mbps); 4x range; 8x broadcasting ability with advertising extensions that increase the advertising packet payload size to 251 bytes, and an improved channel coexistence algorithm.The nRF52840 SoC is supplied with Nordic’s S140 SoftDevice, a Bluetooth 5.2-certified software protocol stack for building long range and high data throughput Bluetooth LE applications. Nordic’s unique software architecture includes a clear separation between the RF protocol software and the developer’s application code, simplifying development and ensuring the SoftDevice doesn’t get corrupted when developing, compiling, testing, and verifying the application code. 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.

“The most important factors in our decision to select Nordic’s nRF52840 SoC for Bubble were the chip’s powerful Arm CPU capability, large memory capacity, and power consumption,” says Chuck Link, President and CTO of M2MD Technologies. “Our company’s familiatiry with the Nordic development environment, coupled with the availability of the Nordic SDK [Software Development Kit], were also key features.  

“Nordic has the best availability, depth, and accuracy of technical documentation online for all developers, large and small, without significant licensing fees. In addition, the technical support provided by Nordic is superb. The large user community and the massive Nordic DevZone forum aided the high speed of our development process.” 

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