Acquisition and elaboration of cardiac signal in android Smartphone devices

Today, the broad proliferation of Smartphones and Tablets has determined a wide availability of software applications for numerous purposes. Thanks to this, Smartphones are now essential devices for many aspects of everyday life and not just advanced mobile phone terminals. The presence of powerful processing units, embedded sensors as well as the availability of many standard communication interfaces has recently attracted the interest of the scientific community. Several projects based on Smartphone systems have been proposed in different fields and many more application scenarios are being explored. A critical aspect still unresolved is the possibility of acquiring external information, such as data from other sensors. Due to their nature of consumer devices, Smartphones provide digital and high level communication interfaces, such as USB and Bluetooth. Sensor interface is therefore possible if a suitable front-end able to digitize sensor data and to handle the communication with the Smartphone is employed. In order to lower the complexity and the cost of the front-end as well as to reduce its power consumption, an effective method for the acquisition of external sensor signals through the Smartphone audio input is proposed in this paper. As a proof of concept, a sensor system composed by a photoplethysmographic sensor for cardiac signal monitoring and a pair of electrodes for tissue impedance estimation has been used. Specific software routines for Android operating system have been developed to process the acquired sensor signals providing visualization, data storage and simple data analysis, and thus demonstrating the feasibility of the proposed approach.