Design of flexible, low-power and wireless sensor nodes for human posture tracking aiding epileptic seizure detection

We present the design of sensor nodes for human posture tracking purposes. Each sensor node is equipped with a microcontroller, an RF transceiver chip and two sensors: a 3D accelerometer and a 3D magnetometer. Based on the signals of these sensors, the orientation of a sensor node can be estimated. Combining several of these nodes into a sensor network, allows for complete human posture tracking, as the human body can be approximated as a rigid body consisting of 15 links. The sensor nodes are designed on a single conductive layer and are assembled on a thin, flexible poly-imide substrate. The microcontroller code has been optimized for low power consumption, while keeping in mind the desired performance. Data is read from the sensors and transmitted wirelessly to a receiver at a rate of 100 samples per second, while only consuming an average current of less than 3 mA. The wireless communication protocol is based upon TDMA and allows for simultaneous use of 10 nodes per receiver.