Travel activity wearable tag


I developed a wearable system using a sensor tag, that operates similar to Fitbit, but for travel activities instead of fitness activities. The user wears/carries the tag during the day, and can later sync it with the phone via Bluetooth to view the travel timeline and statistics.

Tag on wrist
Tag Sync
Travel Timeline

I make novel use of the low-power barometer (air pressure) and step counter sensors, and lightweight algorithms that can run on the extremely resource-constrained tag, which has only about 7 kB of free RAM, 512 kB of external flash storage, and a 220 mAh coin cell battery. The tag can last upto 7 days (21 days for a 600 mAh coin cell).

Experience gained

Android app development

Contemporary app design (single activity with multiple fragments), recycler views, rich notifications, action bar, Firebase login and storage, image caching, using animations, calendar views, card views, floating action buttons, dialog fragments, fragment-fragment and fragment-service communication, responsive GUI layouts, shared preferences, showcase views

Embedded system programming

TI RTOS, Contiki, tasks, message handling, optimizing display power, SPI programming, resolving pin clashes between screen/flash/debugger, power measurement using Monsoon power meter


Ported the step counter driver from Invensense to the sensor tag (including loading the DMP firmware), use of environmental and motion sensors for context detection, sensor batching using hardware FIFO buffers, interfacing 3 lead ECG (heart rate) sensors

Bluetooth Low Energy

Slave side (sensor tag): implementing custom services and attributes, use of rapid notifications for faster data sync, beacon scanning (additional observer role); Master side (Android): scanning, connecting, and receiving notifications

Tag with screen

Applications and Features

  1. View the step count breakdown based on activity

    Step count breakdown
    Timeline edit menu
  2. Personalize place names and add custom activities:
    • At the end of the day, by modifying the timeline
    • In real time, via a rich notification
    Activity Personalization
    Rich notification
  3. View photos taken during the day in the travel timeline
  4. Login and backup data using Firebase

    Photo Timeline
    App side menu login
  5. Check previous day timelines from a drop-down calendar

    App Calendar
    Timeline Example2