Sensor Watch

A hackable ARM Cortex M0+ upgrade for a classic Casio wristwatch

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Sensor Watch is, at its core, a hackable upgrade for the classic Casio F-91W digital wristwatch. It is a replacement for the standard quartz movement in the form of a custom circuit board powered by an ARM Cortex M0+ microcontroller (the Microchip SAM L22).

Among other features it has approximately one year of battery life, a USB port for programming code onto the watch, and a nine-pin flex connector that allows the user to add small "sensor boards" inside the watch case. We have also written a C-based SDK for building watch apps, which makes writing and running your own software easy.

Take Control of Time

Use the watch board as is for applications like timekeeping and alarms. You can also write your own algorithms for alternate calendars and time systems: a decimal-time app, for example, or the Mars Clock for which we’ve written a demo. Timekeeping customization also opens the door to more advanced informational displays like moon-phase indication, sunrise and sunset times, tide tracking, astronomical calculations, and even time-based authentication schemes like TOTP.

But the real power of Sensor Watch comes from its sensor-board connector. Our design reserves a small area inside the watch case for additional components mounted on a flex PCB. By adding components like temperature sensors, light sensors, or accelerometers, you can adapt Sensor Watch to any number of use cases, from step tracking to environmental sensing.

Features & Specifications

  • ARM Cortex M0+ microcontroller
  • 32 kHz crystal for real-time clock functionality with alarm support
  • Red & green PWM’able LED backlight (red & blue on early-bird boards)
  • On-board USB Micro B connector
  • Reset button with double-tap UF2 bootloader
  • Nine-pin flex PCB connector for sensor boards
  • Controller for ten digit segment LCD, plus five indicator segments
  • Edge-plated contacts for three interrupt-capable buttons
  • Connection pad for piezo buzzer (requires light soldering)

Open Source

For folks who just want to make use of the watch and not have to code for it, there is a community firmware project that implements some useful functionality, with more on the way. Flashing code onto the watch is as easy as plugging it in to USB: it shows up as a thumb drive, and you can drag a compiled firmware blob onto it.

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