Simultaneously connecting devices through bluetooth smart

Modern data loggers record and store large amounts of data from many different types of sensors. This enables their use in various applications to capture different measurands. However wireless access to the recorded data opens countless possibilities for novel and innovative applications, for example in the health monitoring of humans or livestock. In many of these applications a central device connects simultaneously to several data loggers. This paper discusses the experiences made during the design, implementation and test of an energy efficient wireless interface to a data logger. The implemented system serves as an application example for Bluetooth Smart. It allows a user to monitor ongoing measurements of several data loggers through a smartphone. Additionally the recorded data of several loggers can be simultaneously uploaded to a central gateway. The available Bluetooth Smart chips and software stacks place limitations on usable bandwidth as well as on the number of simultaneous connections. Although most modern smartphones include hardware for Bluetooth Smart, implementations differ widely across platforms, thus creating additional effort for the app programmer. This paper presents measurement results and introduces the implemented approaches to optimize these parameters