Sensor Watch: a board swap for the classic Casio F-91W wristwatch

www.sensorwatch.net · 2026-08-20 · by Long Nguyen ·generic

Sensor Watch: a board swap for the classic Casio F-91W wristwatch

Sensor Watch: a board swap for the classic Casio F-91W wristwatch

Get Started Order at Crowd Supply

Sensor Watch is a board replacement for the classic Casio F‑91W wristwatch. It is powered by a Microchip SAM L22 microcontroller with built-in segment LCD controller. You can write your own programs for the watch using the provided watch library, program the watch over USB using the built-in UF2 bootloader, and then install the board in your existing watch case to run your own software on your wrist.

Photo: a close-up of the Sensor Watch circuit board, and a wristwatch displaying the word “Hello”

#### Smart ARM power

Sensor Watch is powered by the Microchip SAM L22, an ARM Cortex M0+ microcontroller with tons of powerful peripherals.

#### Long-lived battery

Sensor Watch sips single-digit microamperes of power, making this a watch you can wear all year on a single coin cell.

#### Timeless Timekeeping

A highly accurate 32.768 KHz crystal keeps accurate time — and displays it on the original F-91W LCD for a classic look and feel.

#### Light and sound

The LED backlight supports shades of red, green and yellow. With light soldering, you can also use the F-91W’s piezo buzzer.

#### Sensor Extensible

A 9-pin connector breaks out an I²C bus and five GPIO for SPI, UART or analog input, letting you add sensors to Sensor Watch.

#### Open Source

Fully open source hardware and software allow you to buy one or build your own — and remix the firmware to suit your taste.

Preorder at Crowd Supply!

#### Join the Sensor Watch Discord!

Chat with other Sensor Watch users and get help with your own Sensor Watch build.

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#### Contributions welcome!

We do a Pull Request contributions workflow on GitHub. New users are always welcome!

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#### Follow along on Twitter!

Get the absolute latest from the developer of Sensor Watch, plus other posts.

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