Bench Talk

Image Source: Mouser Electronics

Healthcare providers around the world are facing a range of challenges as populations age and life expectancy rises. In some ways, it’s a good problem to have, highlighting that campaigns to encourage healthier lifestyles and advancements in healthcare have had an impact. According to the OECD Health at a Glance: Europe 2024 report,^[1] life expectancy at age 65 now exceeds 20 years. However, with more than half of these years being impaired by chronic illnesses and disabilities, healthcare providers are being placed under ever-greater pressure.

More Data Earlier Makes Diagnosis Simpler

The primary issue is workforce shortages. But addressing this issue alone isn’t enough to deal with the wave of healthcare challenges coming our way. In parallel, healthcare providers are looking to technology, such as the Internet of Medical Things (IoMT), to monitor heart rate, blood pressure, oxygen level, glucose level, and respiratory rate^[2] to improve early detection of illnesses and avoid more complex and expensive healthcare needs (Figure 1).

Figure 1: By offering continuous measurement of vital signs using IoMT devices, such as a blood pressure cuff, doctors develop a fuller picture of their patients’ condition. (Source: Oksana Klymenko/stock.adobe.com)

Consumer smartwatches have already demonstrated their ability to reliably detect certain heart conditions. One user in Nova Scotia, Canada, was informed by their device of a possible atrial fibrillation (AF), an irregular heartbeat, giving doctors a head start when he called for help.^[3] In a screening of over 400,000 Apple Watch users by the American College of Cardiology, a third of those who received a warning were confirmed to have AF.^[4]

Accessing the Data

The ubiquity of wireless connectivity and advanced battery technology clearly makes it easier than ever to collect health data from wearable devices for analysis. The next question, then, is: Which wireless tech is most appropriate?

Bluetooth^®, especially Bluetooth Low Energy, is an obvious choice if the patient has access to a suitable smartphone with an up-to-date operating system for the supporting app. LTE-M and NB-IoT provide good coverage and enough bandwidth, but require more complex management due to cellular contracts. Additionally, they, like smartphones, pose risks to critical care equipment.^[5]

This leaves Wi-Fi. Available in the majority of homes and already deployed for multiple purposes in clinics and hospitals,^[6] it is a technology that even non-technical users are familiar with. Furthermore, it already supports secure connections, simplifying the implementation of an end-to-end cybersecure IoMT product.

Calypso: Secure Wi-Fi in Module Form

Adding wireless support to applications has become incredibly simple thanks to modules that integrate a suitable PCB antenna. That solves part of the issue. However, challenges remain in implementing security and developing the application. One popular approach is to deploy the full Wi-Fi stack in a module, allowing developers to choose a microcontroller (MCU) best suited to the rest of the application. This is the approach open to users of Würth Elektronik’s Calypso Wi-Fi^® Radio Module.

With a fully featured TCP/IP stack and support for the IEEE 802.11b/g/n standards, configuration and operation require only a UART interface from the host MCU and the implementation of an AT-style command interface. The module features castellated edges, making it simple to add to a PCB and integrate into a pick-and-place manufacturing flow. An integrated smart antenna selection allows an external antenna to be attached via a 50 Ω feed line (Figure 2).

The module requires a nominal 3.3V supply and is specified for -40°C to +85°C. For battery-powered applications, it is worth noting the impact of the older Wi-Fi standard (802.11b) on power consumption. Using DSSS coding, the average current draw at maximum transmit power is around 260mA compared to around 120mA with the OFDM coding used in the more modern 802.11g/n standards. In low power mode, the module draws 10µA.

Figure 2: With its castellated edges and integrated antenna, the Würth Elektronik Calypso Wi-Fi module is simple to integrate into your PCB design and manufacturing flow. (Source: Mouser Electronics)

Several network applications are ready to use, including SNTP, DHCPv4, DHCPv6, mDNS, HTTP(S), and MQTT, supporting both IPv4 and IPv6. In terms of security, the module supports secure boot, secure certificate storage, secure over-the-air (OTA) updates, and up to six secure sockets.

Two pins are used to define functionality after power-up. Two combinations offer variants of the AT command interfaces, while a third puts the module in a mode ready for an OTA update. For embedded devices with limited or no suitable human-machine interface (HMI), the fourth mode enables provisioning. This brings the module up as an access point (AP), allowing users with the necessary credentials to access the on-module HTTPS webserver and configuration options (Figure 3).

Connection to a host MCU requires only the UART TX/RX pins, but RTS/CTS flow control can also be implemented if needed. The standard Baud rate is 921,600, but it can be set between 115,200 and 3,000,000.

Figure 3: Combinations of two input pins set the start-up mode of the Calypso module. The intelligent antenna switch supports the use of an external antenna. (Source: Würth Elektronik)

Simplified Wi-Fi Operation Modes

Not every application requires full cloud connectivity or the full features of a TCP/IP stack. Sometimes it’s enough to have a simple wireless control feature or a data link. For applications that simply need to transfer data wirelessly from A to B, Calypso offers a UART-to-Wi-Fi bridge capability. Once a connection has been established, the module provides a clean serial interface to another device or a PC terminal via a router. Depending on the configuration, throughputs of up to 82kBytes/s can be attained.

Another feature, Remote GPIO, allows a device on the Wi-Fi network to directly control up to four GPIOs (two input/output and two input/output/PWM) without intervention from the host MCU. When connected, this feature can also be controlled via a web browser and the dedicated GPIO GET/SET page.

Exploration of full cloud-based IoMT applications can be undertaken using development tools such as the Calypso IoT Design Kit, which targets evaluation of the module together with Microsoft’s Azure IoT Central (Figure 4).

Figure 4: Trialling a complete IoMT application linked to Microsoft’s Azure IoT Center is possible using the Calypso IoT Design Kit. (Source: Mouser Electronics)

Add Wi-Fi While Focusing on Your Application

Adding TCP/IP-based connectivity to embedded systems has become steadily more complex as standards have evolved and product cybersecurity has come under ever more scrutiny. In such cases, it makes sense for IoMT development teams to focus on their area of competence and product differentiation by implementing secure wireless connectivity using a dedicated module. Calypso provides a certified Wi-Fi interface and support for a broad range of Internet technologies, using up-to-date security methods. This approach also allows a microcontroller to be selected that matches the application’s needs and complexity, and avoids the need to develop software and select hardware suited to handle issues such as secure OTA updates and certificate storage.

Sources

[1] https://www.oecd.org/en/publications/health-at-a-glance-europe-2024_b3704e14-en.html
[2] https://www.sciencedirect.com/science/article/pii/S0925231223011402#ab0015
[3] https://globalnews.ca/news/10567186/apple-watch-notifys-man-having-heart-attack/
[4] https://www.reuters.com/article/world/apple-watch-detects-irregular-heart-beat-in-large-us-study-idUSKCN1QX0EJ/
[5] https://pmc.ncbi.nlm.nih.gov/articles/PMC2738319/
[6] https://gblogs.cisco.com/uki/the-importance-of-wifi-for-hospitals-and-patients