Backstory

crowdsupply

I saw the crowdsupply in april 2025 and thought that its absolutely crazy idea, a hackable watch, while still very limited, no bluetooth, no internet, just static data and accelerometer and temperature sensors. Thats so nerdy that i had little hope it would get funding. Few months later, my mum and brother asked me what i want for birthday and i said i don’t know (as always) but then days later i asked for the sensor watch pro with custom lcd, accelerometer and new casio f-91w to go with it. I looked forward to program my own watch faces. I thought of the metronome, pomodoro timer and watch face that will show me countdown to the nearest train departure on my way to work.

I hope to explore more whole ecosystem, software stack, how to develop new watch face and so on but first, i wanna install it and wear it for a while.

Installation

unboxing

Everything was so neatly packaged, and the F-91W is very comfortable - compared to my g-shock 5522. At first i thought: ok i have a pcb but how do i flash it? Do i have to order some 3D printed parts to connect to the debug pins? Oh boy no, the small cutout is designed to plug directly into a USB Micro B cable

unboxing

This set my expectations very high. The person/s who designed this are very smart.

I opted to install the new refactored firmware from github. The compilation was fast and easy, i event tested the emulator (!!!!!!!). I was not very smart tho - the usb cable i used was power only so i spent 10 minutes debugging why is the watch not mounting on my mac.

emulator i could not believe it, just wau

After flash i disassembled my new watch i received that day and wore for just few hours. Felt weird, i was worried i’ll break something. Following the amazing guide i had it done in less than 20 minutes even replaced the lcd in the process.

last-photo last photo before dissasably

whats-left the original movement - the green pcb, original lcd and new assembled sensor watch pro movement.

Features

OG F-91W

First lets review all the features the casios from the 80” have.

  1. Time with 12/24h switch
  2. Stopwatch
  3. Alarm
  4. Hour announcement

Sensor watch Pro

Not bad but now let me list features build in the second-movement.

  1. Time
  2. World time
  3. Sunrise/Sunset
  4. Moon phase
  5. Stopwatch
  6. Countdown
  7. Alarm
  8. Temperature - Celsius or Fahrenheit
  9. Battery Voltage
  10. Settings
    1. 12/24h switch
    2. Volume of buttons
    3. Timeout - the time until screens snap back to the first screen
    4. Low energy mode
    5. LED backlight
      1. Instant/1 sec/3 sec/5 sec/No LED
      2. RGB set from 0-15 for every color

Finished assembly

It really took me 30 minutes from cloning the github repo to reassembled watch.

time Custom lcd!

batt Battery voltage screen

temp Temperature screen

nyc-time World time screen

Another cool things:

The timer (Countdown) watch face has a quick “touch” input thanks to the accelerometer.

Config is stored on device!

Second Movement now stores your configuration on the little file system on Sensor Watch! This means after you change the battery — or simply crack open the watch to swap out the firmware — your preferences, time zone and location will be right where you left them. source

Game using accelerometer as an imput Endless runner port

tbd: Significantly improve off axis viewing for custom LCD by faldor20 …