e-Ink Tattoo

Experimental Interface

Problem Statement

Athletes and fitness enthusiasts who are serious about improving often have complex workout routines and need to keep track of their progress. This means memorizing everything or carrying around a notebook and pencil, cellphone, tablet, or other device.

Pair this with a handheld stopwatch or wrist watch and an iPod with headphones and you’re left with distractions that impair the quality of a workout.


The technology to make this a reality could be invented within 50 years.


Nine weeks

Trend research

Today’s fitness trackers range from $50-250 in three main form factors: bracelets, clip-ons, and watches. Some track sleep, and some are sport specific. Because these devices are made to be convenient to wear when working out, they require a companion app on a cellphone or desktop to view advanced data metrics.

All of them are battery operated which means they need to be recharged every night or can run up to a few weeks, but need the battery changed after that.

Design research

1sp (skin pixel) = 0.25mm = 0.94px = 0.71pt
Smallest average forearm size: 220 x 70mm = 880 x 280sp
Thinnest tattoo needle: #6 needle at 0.20mm = 0.8sp
Minimum line weight: 0.25mm = 1sp
Minimum type size: 3.53mm = 10pt = 14sp
Touch target size: 7-10mm = 28-40sp
Information zones: Least important to most important
Responsive mode: Horizontal to vertical, inside to outside
Alternate display: Outside wrist, hand
Alternate interactions: Gesture based
Skin color: All supported

Technology research

Atmel® ATBTLC1000-MR110CA Bluetooth Low Energy module
    - $11 per unit (low volume)
    - 2 × 2mm
    - 1.8 – 4.3V

Quallion QL0003I Li-ion cell
    - 2.9 x 11.8mm
    - 3mAh at 3.6V
    - Implantable
    - Extended cycle life

E-ink two-pigment subdermal display


My sketches helped visualize where on the arm the tattoo would be best located for easy interaction and visibility. I also explored some gestured-based controls for hands-free interaction.

  • "Open" button
  • Opened state

    1) Close apps; 2) App icons

  • Vertical arm orientation
  • Vertical arm orientation
  • Adjust position of interface on arm

    Options: Power off, move up/down, lock position

  • Heart rate monitor

    1) See and move target heart range; 2) Current BPM

  • Exceeded BPM alert

    1) Responsive graph minimizes to the side; 2) Warning appears with explanation

  • Stopwatch mode

    1) Stopwatch currently selected; 2) Watch is paused

  • Stopwatch mode

    1) When the watch is active, the menu decreases in size to call less attention; 2) Split times scroll up the arm as added

  • Timer mode
  • Timer mode

    1) Drag up or down to change the time; 2) Start timer when ready

  • Timer mode

    1) Timer is active

  • Music player

    1) Controls in the middle; 2) Music visualization is cool to look at, but not distracting; 3) Current track information

Final design