ETHOS

Contact: Holger Harms

Project start: Spring 2010

Contributors: Rene Winkler, Martin Kusserow, Thomas Fahrni, Florian Deragisch, Jonas Huber, Fredy Mettler, Johannes Schumm, Oliver Amft

The ETH Onbody Sensor (ETHOS) implements a wearable sensor platform that is optimized for long-term monitoring of human body-segment orientation. The core component is an inertial measurement system (tri-axial accelerometer, earth magnetic field-, and gyroscope sensors). An internal temperature sensor, used for compensation of sensor drifts, can be interfaced, too. Gathered data can be stored in a raw format, or fused by an on-board DSP to an orientation in an Euler-angle representation. In both cases, data can be transmitted via wired (USB) or wireless interface (ANT+) for real-time display, and stored on internal non-volatile memory for offline analysis after the recording.

Comfort and wearability

Advances in MEMS technology allowed a miniaturization of the PCB dimensions to 16x6x42mm³ (WxHxL). In a stacked housing version, ETHOS meets a dimension of 18x14x45mm³ (WxHxL). An alternative housing option was designed for an unobtrusive attachment of the system to body limbs. The sensor PCB and battery are aligned side by side and form a half-shell that is worn like a bracelet with an overall height of less than 10mm.

Long-term operation

ETHOS was pushed on hardware- and algorithmic levels to achieve a maximum system runtime. The system achieves an operation of more than 15 hours, if orientation is computed with a frequency of 128Hz and a miniature 300mAh battery pack is used. However, sampling- and transmission frequency are configurable to meet a practicable compromise between battery runtime and required information density.

Scalability

An integrated ANT+ connectivity allows for the formation of scalable body-area-network (BAN). The BAN can include other ETHOS units and/or every ANT+ compatible hardware. Synchronization is guaranteed by real-time-clock (RTC) information.

Publication

ETHOS: Miniature Orientation Sensor for Wearable Human Motion Analysis
Holger Harms, Oliver Amft, Rene Winkler, Johannes Schumm, Martin Kusserow and Gerhard Tröster In: Proceedings of IEEE Sensors conference, IEEE, 2010

Projects working with ETHOS