An open NFC-based platform for vital signs monitoring

This paper presents an open, low-power, wireless and wearable platform for continuous monitoring of clinical signs in health-care scenarios, both indoor and outdoor. The platform has been designed in order to overcome the limitations of well-known technologies for wearable architectures as detailed in [1] (e.g. battery lifetime, lack of open source codes, ...). Since several devices on the market use Bluetooth for data communication (the operational lifetime is limited to few hours and the user intervention is often required to recharge or change the battery), the platform integrates reliable, safe and low-power Near Field Communication protocol (NFC) for data transmission in proximity, addressing the new Internet of Things (IoT) paradigm. The first prototype of the platform (35mm?30mm?15mm, 13g weight) has been customized for human body temperature measurement (NTC thermistor [2] for biomedical applications) and control (up to 16 MIPS), although a real "ecosystem" of wearable devices could be prototyped with low-effort for the acquisition/transmission of other kind of clinical signs (e.g. heart-rate, breath-rate, ecg, ...), by using both micro-sensors and textile sensors and tunabled read-out circuit. The platform uses a SonyFelica NFC Dynamic Tag module [3] as best trade-off between operation range communication (up to 10 cm) and power consumption in healthcare scenarios. It is preferred to the widely used Bluetooth protocol due to the extremely limited power consumption, avoiding pairing steps since NFC tags establish a peer-to-peer connection with mobile devices in automatic way in less than 0.1s. The software platform uses the Arduino programming language and the GNU Arduino libraries [4], so it could be possible to add new functionalities in open way. The relative block diagram and the discrete prototype circuit are shown in Figure 1 and Figure 2, respectively. Low-power electronic components are used during the design; a good trade-off between computational workload and power consumption for the acquisition, real-time computing and data transmission is for 4MHz operating frequency of Atmega328p microcontroller. As shown in Table1, the maximum total current consumption of the system is about 16mA at 4 MIPS: the power consumption is dominated by the local alerting part that is only activated when a critical situation is detected (in normal mode the maximum total current consumption is less than 5mA). The system is supplied by micro-power Low-DropOut (LDO) CMOS voltage regulators with a low temperature dependence and the shutdown pin for reducing supply current close to zero. Through a proper management of each electronic components, a long battery life is provided (more than 2 months, with a 10 minutes time sample and a 600mAh lithium battery). The first prototype of a customized package (a watchstrap made in Polylactic Acid by a BQ Witbox 3D printer) and the relative mobile App are shown in Figure 3; approaching the smartphone to the wearable device, the values of body temperature can be read instantly and automatically by the users/caregivers.