With Watch+Strap we propose to enrich smartwatches with interactive StrapDisplays in order to extend their input and output capabilities.

Watch+Strap in 4 Minutes

In a hurry? We also have a 30-second preview video.

Abstract

While smartwatches are widely adopted these days, their input and output space remains fairly limited by their screen size. We present StrapDisplays—interactive watchbands with embedded display and touch technologies—that enhance commodity watches and extend their input and output capabilities. After introducing the physical design space of these StrapDisplays, we explore how to combine a smartwatch and straps in a synergistic Watch+Strap system. Specifically, we propose multiple interface concepts that consider promising content distributions, interaction techniques, usage types, and display roles. For example, the straps can enrich watch apps, display visualizations, provide glanceable feedback, or help avoiding occlusion issues.

Further, we provide a modular research platform incorporating three StrapDisplay prototypes and a flexible web-based software architecture, demonstrating the feasibility of our approach. Early brainstorming sessions with 15 participants informed our design process, while later interviews with six experts supported our concepts and provided valuable feedback for future developments.

Presentation @ ACM CHI ’20

The paper is published in the Proceedings of the 2020 CHI Conference. It was planned to present our Watch+Strap paper at the conference in Honolulu, Hawaii, USA in April 2020, however, the conference had to be canceled. Instead, we are providing a recorded talk on YouTube:

You can also watch our shorter 3 minute presentation from the 2020 Virtual German CHI Week.

Publication

Source Code & Online Documentation

One main contribution of our Watch+Strap paper is its open research platform. For that, we provide all materials in the following. The source code of the Watch+Strap components as well as the used 3D models are made publicly available on Github. Specifically, our project consist of three repositories:


Application Server
The application server for the Watch+Strap prototype, which is running all application logic. Watch and StrapDisplays connect to this server. github.com/imldresden/WatchStrap-app-server
Tizen App
Simple Tizen application for connecting a Samsung Gear smartwatch to the Watch+Strap application server. github.com/imldresden/WatchStrap-tizen-app
E-Ink StrapDisplays
Firmware and 3D-Models for the Arduino-based E-Ink StrapDisplays that connect to the Watch+Strap application server can be found on this project website.

Building Instructions: E-Ink StrapDisplays

In the following, we will describe how our E-Ink StrapDisplays are constructed and present detailed building instructions.

1. Preparing the Membrane Potentiometer

Partlist for Membrane Potentiometer
Image Part Description
ThinPot Film Potentiometer
l=50mm;
TSP-L-0050-103-3%-ST
We used three ThinPot Film Potentiometer from Spectra Symbol to continuously measure pressure input in three lines. Available, for example, at Mouser, Digi-Key or Reichelt Elektronik.
Transparent Film
2mm
Highflex Cable
0.05mm²; PVC 0.8mm;
10×0.08mm
Available, for example, at Conrad Electronics.
Heat Shrink Tubing
d=1.20mm; ratio: 2:1
Machine Male Pin Headers

2. Adding the E-Ink Display

Partlist for the e-ink prototype
Image Part Description
Flexible e-Paper display
2.13inch e-Paper (D); SKU 14986
e-Paper Adapter
Flex Connector Cable
AWM 20624; 24 Pin
Double Faced Adhesive Tape

3. Finalizing the StrapDisplay

Partlist for the e-ink prototype
Image Part Description
Quick Release Spring Bar
l=22mm
Available, for example, at Amazon.
Sewing Kit
Velcro Ribbon
Double Faced Adhesive Tape

3D models for the e-ink prototype
3D Model Description
Strap Housings
strap_e_ink_housing.stl
strap_e_ink_housing_cover.stl

First, we glued a piece of velcro on the back of the StrapDisplay housing. To strengthen the connection, we also sewed the velcro since closing and opening the velcro continuously exert forces to the adhesive connection. As a next step the flexible E-Ink display and membrane potentiometers must be slid into the housing.

In order to cover and protect the breakout of the strap electronics, we designed a cover that could be seamlessly slide above the strap without the need of any glue. However, please take care that you did not damage any cables or connectors.

4. Building an Analog-Digital-Converter Shield

Partlist for the e-ink prototype
Image Part Description
e-Paper ESP8266
Driver Board
16Bit ADC
ADS1115; 4 Channel AD; SKU:18443
10k resistor
Prototyping PCB
Phenolic paper
0.1″/2.54mm,
80mm x 52mm, 35µm
We used these prototyping boards as a basis for our circuits. Available, for example, at Conrad Electronics.
Small Female Pin Headers
Male Pin Headers
Jumper wire
YV; white; cross section: 0.2mm² ; outer:1.1mm

5. Creating a Housing for the Electronics

Partlist for the e-ink prototype
Image Part Description
Sewing Kit
Velcro Ribbon
Elastic Ribbon

3D models for the e-ink prototype
3D Model Description
Electronics Housing
controller_housing_base.stl
controller_housing_cable_config.stl
controller_housing_cable_fixation.stl
controller_housing_cover.stl

6. Program the Microcontroller

The Arduino source code for the E-Ink prototype can be downloaded here:
strapdisplay-e-ink-prototype.zip

*Please note that we slightly modified the Adafruit_ADS1015 library for our prototype. The customized version is part of the zip download package.

7. Final Assembly

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