Open Activity Tracker Framework

We are developing an open-​source framework for continuous and reliable physical activity tracking at low cost. The framework delivers researchers and clinicians a transparent and easy-​to-configure tool for tracking activity in large cohorts. Researchers have full control over signal processing and data streams, making the proprietary cloud based services hosted in unknown locations obsolete.

MHSL Activity Tracker

The MHSL Activity tracker was originally developed at the Mobile Health Systems Lab at ETH Zürich and is a wearable electronics module that builds the core of the open-​source physical activity tracking framework.

Key features:

  • High-​end, low power 3-​axis accelerometer operating at up to 400 Hz, with a selectable acceleration range of ±2g, ±4g, and ±8g (ADXL363)
  • 16 MB on-​device Flash memory IS25LP128 (enables approx. 48 hours of raw data recording from 3 axis, at 12-​bit resolution and 12.5Hz sampling rate)
  • Up to 6 months of stand-​alone use, storing one 16-​bit-word/minute
  • Bluetooth connectivity for real-​time or offline data acquisition
  • Powered by an exchangeable coin-​cell battery (CR3032) providing up to 6 months life-​time
  • Button and 2 LEDs for simple user interaction
  • Small, circular PCB with all electronics integrated (2.5cm in diameter)
  • 3D-​printed housing for modular packaging solution (current version supports attachment of Swatch armbands and enclosing into velcro elastic bands for comfortable wearing at the wrist and ankle)
  • Open-​source mobile app (Android) for actimeter configuration and data collection, analysis, and visualization
  • Open-​hardware for easy adaptation of housing or changing electronic components according to projects-​specific requirements
  • Large selection of open-​source algorithms tested for various applications (activity measure, sleep tracking) and wearing positions (ankle, hip, and wrist)

Research projects where the framework was in use:

ETH Scientifica (2017): Twenty actimeters have been successfully used at the 2017 ETH Scientifica citizen-​science project “Was sagen Aktivitätsarmbänder und SmartWatches wirklich über unsere Aktivität aus?» demonstrating a MIDATA integration with different health applications.

SNF NFP75 Big-Data (2019-2020):  The actimeters have been used to monitor low-back pain patients during the intervention period in a clinical trial investigating exergaming interventions. 

Meinke, A., Peters, R., Knols, R., Karlen, W., & Swanenburg, J. (2021). Exergaming Using Postural Feedback From Wearable Sensors and Exercise Therapy to Improve Postural Balance in People With Unspecific Low Back Pain: Protocol for a Factorial Pilot Randomized Controlled Trial. (Preprint). JMIR Research Protocols.

Developers and Collaborators:

Prof. Walter Karlen, Dr. Jelena Dragas, 

We are collaborating with a Swiss-​based startup Leitwert GmbH who have designed the hardware and real time embedded software.

Prof. Dr. Christina Spengler, Exercise Physiology Lab, ETH Zürich




J. Dragas and W. Karlen, "Open-Source Low-Cost Wearable Physical Activity Tracker" in 3rd WHO Global Forum on Medical Devices, Geneva: World Health Organisation, 2017.


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