The sensor is part of the equipment positioned in the joint under consideration. Each sensor is constituted by a microcontroller, a three-axis accelerometer and a processor network . The microcontroller communicates with the accelerometer chip through a Serial Peripheral Interface ( SPI ) . When prompted , the accelerometer chip microcontroller sends the values of X , Y and Z corresponding to the force vector ( Gaino , 2010) . From these values the microcontroller assembles a data packet to be sent via wireless communication . The processor sensor network is restricted to connecting to the network , and is therefore called end device .