A Light-Bulb Moment for Smartwatch Developers

Many electronics hobbyists spend their free time working on DIY projects because they can't find commercial products that perfectly match their specific requirements or interests. Designing a device from scratch gives them the freedom to build in every single feature they want. However, there is a trade-off as well. In general, these homemade solutions lack the polish of a commercial product. As a result, these creations often find themselves relegated to the spare parts bin before long.

A pair of engineers at the University of Calgary came up with a different approach to this problem. They think that if we can find a commercial device that already does most of what we want it to do, then the ideal solution may be to add a few things to it, rather than start from scratch. Manufacturers do not exactly make this easy, however, so the team had to get creative in their approach.

The researchers focused on smartwatches, and came up with a universal solution called LightLink that allows hobbyists to add sensors, actuators, and more to commercial hardware. These components would typically be hardwired into the system, or would at least communicate with the watch via Wi-Fi or Bluetooth. But without support from the manufacturer, that may not be possible. So the team came up with a communication protocol for add-ons that sounds more like something out of the 1990s than the 2020s.

LightLink relies on visible light as its data channel. Most modern smartwatches already include two key components that make this possible: a screen that can rapidly change brightness and an ambient light sensor that measures surrounding illumination. By treating the screen as a transmitter and the light sensor as a receiver, the researchers created a low-cost way to pass information back and forth. To complete the link, external add-on devices use simple components like LEDs and photodiodes to exchange data with the watch.

To make this possible, an external sensor, such as a thermometer, can modulate the brightness of a small LED based on its readings. The watch’s ambient light sensor detects those subtle flickers and translates them into temperature data that can be displayed in real time. For communication in the opposite direction, the smartwatch dedicates a small region of its display to rapidly flashing patterns that encode commands. A photodiode connected to the add-on device detects these changes and sends them to a microcontroller, which may then drive an actuator such as a motor or light. This setup enables true bidirectional communication without the need for custom firmware or manufacturer support.

The team demonstrated eight different add-ons ranging from simple buttons and temperature probes to more advanced modules like infrared transmitters and haptic feedback wristbands. All of these functioned as expected with existing smartwatches, showing that the system could expand both sensing and output capabilities without complex modifications.

LightLink reimagines the smartwatch not as a fixed product, but as a flexible platform ready to be customized. For DIY enthusiasts, it might just keep those projects out of the spare parts bin for good.