Simplifying Bluetooth Low Energy medical device design


A new Nordic Proof-of-Concept PCB makes it less complicated for developers to bring the benefits of wireless connectivity to medical devices.

Pioneering medical product companies are already improving the lives of diabetes-, allergy-, and asthma-sufferers by equipping their products with Bluetooth Low Energy (Bluetooth LE) technology. For example, Canadian company, Aterica Health, has developed Veta Smart Case, a Bluetooth LE-connected carrier for Epipen auto-injectors. San Diego, CA-based Dexcom meanwhile, recently received U.S. Food and Drug Administration (FDA) approval for its G5 Mobile Continuous Glucose Monitoring (CGM) System which includes a Bluetooth LE component to transmit glucose levels from a monitor mounted on the patient’s skin to a companion app on a smartphone or smartwatch.

These wirelessly-connected medical products assist patients by reminding them when to take medication, warning when medicine approaches its expiry date, and notifying if vital medicine is left behind when leaving home. In addition, wirelessly connecting the product to the IoT (via a smartphone gateway) establishes a bidirectional link along which not only can data be transmitted to remote family and healthcare professionals but also information returned in the form of guidance for the patient, or software enhancements and security patches for the product.

Wireless connectivity also brings medical economic benefits. By helping patients adhere to a medication regime, money is saved due to a reduction in the complications that could otherwise occur without proper treatment of the primary illness. Another significant benefit is in the value of data that becomes available from the Cloud to help medical equipment manufacturers understand how, when, and where devices and medication are used – leading to better products.

However, RF engineering is a challenging discipline requiring skilled practitioners who are in short supply, making it difficult for many medical product makers to enter the market.

Simplifying design
But now, Nordic Semiconductor has introduced a proof-of- concept (PoC) printed circuit board (PCB) that simplifies the design process. The PoC PCB employs the company’s nRF52810 Bluetooth LE solution and S112 SoftDevice (Bluetooth LE RF protocol software ‘stack’). The product is an extremely flexible, mature, and reliable Bluetooth 5-certified solution optimized for low power and high performance in a tiny footprint.

Nordic’s nRF52810 Bluetooth LE SoC—the baseline device in its nRF52 Series which offers an excellent cost/performance ratio and Bluetooth 5 capability— features a 100-dBm link budget 2.4-GHz multiprotocol radio, 64-MHz, 32-bit ARM Cortex M4 MCU, 196-kB Flash, and 24-kB RAM. Notably, the memory allocation is ample to run the application code typical of high-volume, low-cost applications such as those required for medical devices. Like all Nordic’s nRF51 and nRF52 Series SoCs, the nRF52810 supports Over-the-Air Device Firmware Updates (OTA- DFUs), allowing the software of devices in the field to be upgraded using just the radio link. The nRF52810 SoC is supplied with the latest version of Nordic’s S112 SoftDevice, a lightweight Bluetooth 5-certified stack.

The nRF52 series also brings other features crucial to medical product development, notably “out-of-band” (OOB) pairing via Near Field Communication (NFC), which enables Bluetooth LE pairing to be established by simply touching an NFC-equipped smartphone to the medical device with no other interaction required from the user. Second, once the medical device is paired with the smartphone, sensitive medical data is secured by protecting the Bluetooth LE link with 128-bit AES encryption.

While the S112 SoftDevice supervises the communication link, some application code is typically required to optimize the software for the target product. For example, if the target application is an asthma inhaler, some coding will be required to, for instance, monitor how often and when the device is used.

Among Bluetooth LE vendors, Nordic has a unique advantage during application code development. The company’s software architecture separates the Bluetooth LE stack (the SoftDevice) from the application code thereby removing the complexity of integrating the application software with the stack. Without this separation, it can be all too easy for the RF stack to be corrupted during software compilation – extending the development and debugging process. Nordic’s SoftDevices are delivered as tested and verified binary files and the company’s development tools look after interfacing the application code to the SoftDevice during compilation.

Nordic also supplies a Development Kit (DK) and Software Development Kit (SDK) which eases the design process. The DK includes the target nRF51 or nRF52 Series SoC and the SDK makes it simple to interface the SoC to the developer’s preferred ARM integrated development environment (IDE). Notably, the SDK also includes simple application code examples which the developer can use to accelerate the coding of their own application.

Combining advantages
Nordic has brought together the key advantages of its nRF52 Series SoCs, Bluetooth LE SoftDevices, unique software architecture, reference designs, and application code development environment in the new PoC PCB – a product that’s specifically designed to simplify the process of adding wireless connectivity to medical products.

The PoC PCB is based on the nRF52810 SoC and S112 SoftDevice (enabling Bluetooth 5-certified Peripheral device operation), is assembled on a 13.5-mm diameter circuit board and includes matching circuits, antenna, and coin-cell battery. The PoC and the necessary design files are available from Nordic on demand. The file includes a short description and ‘walk through’, circuit board schematics, and bill of materials (BOM). This is everything a designer needs to develop their own design based on the PoC.

The product comes preloaded with the SoftDevice and an Eddystone Bluetooth LE beacon application example. The nRF52810 SoC can be programmed with the developer’s own application through OTA- DFU. Because the nRF52810 with S112 SoftDevice form a cost-effective Bluetooth 5/Bluetooth LE solution, the Nordic medical PoC PCB is particularly suitable for inexpensive, disposable drug delivery products such as asthma inhalers. According to a report from analyst Market Research Future, the market for ‘smart’ (wireless) asthma inhalers will be worth $1.6 billion alone by 2022.

An inhaler equipped with Nordic’s Bluetooth LE technology would enable medication management (for example, providing an automatic medication diary), notifications to remote family members and healthcare staff, and usage statistics. With permission, the data could also be automatically sent to the manufacturer via the Internet to allow it to improve the performance of future products.

The quiet revolution
A quiet revolution is underway in connected medical products. Because of the tough regulatory environment, it has taken time for these products to reach the market but there are many innovations nearing commercialization. Bluetooth LE is ideally suited for transmitting small amounts of data from power-constrained devices and is appearing in applications ranging from connecting a stethoscope to a smartphone app to simultaneously monitoring the blood pressure of dozens of seniors in a care home and forwarding the data to the Cloud to determine when to administer hypertension medication. And Bluetooth LE wireless’ ubiquity in smartphones and tablets cements its position as the pre-eminent wireless connectivity technology for medical products.

Designing wireless products can be daunting and many medical product companies may not have the in-house RF skills to take advantage of the technology. However, by partnering with a Bluetooth LE vendor like Nordic, developers with little RF design experience gain access to proven hardware, protocol firmware, reference designs, development tools, and technical expertise that ease the path to prototypes and then volume production of commercial devices.

A leading choice

Bluetooth LE technology’s interoperability with smartphones makes it a leading choice for wireless medical products