The Casio F-91W is easily one of the most iconic and popular watches worldwide. But what’s cool about having the same exact thing as millions of other people? Not much, unless of course you modify it to make it your own. That’s exactly what [Gautchh] did to their beloved watch. Between permanent dark mode, stereo blue LED backlights, and a new strap, this timepiece really stands out from the crowd.
Once [Gautchh] got the watch open, the first order of business was to re-polarize the LCD with a different film so the digits are light and the background is dark. This watch ships with a single green backlight LED that’s fairly faint, so [Gautchh] upgraded it to bright blue and added a second 1206 LED in parallel on the other side of the readout. Finally, they replaced the rubber strap with something less likely to chafe.
We think dark mode looks great, though [Gautchh] says it requires a little bit of training to hold your wrist just right to make it readable. They make these mods look easy, but they likely aren’t for the faint of heart. If you want to give it a shot, there are good step-by-step instructions and several pictures to help out.
We’ve seen a lot of Casio F-91W projects over the years, including a method for waterproofing the internals. If you have a lot of love for this watch, why not make a giant version?
19 thoughts on “Casio F-91W, Going Dark”
Isn’t this this watch that all the terrorists use?
That’s soo 2000-and-late.
*covers wrist with hand*
I am sure that we did this with our watches way back in the 80s by simply flipping the polariser.
(But I accept that I might be both sure, and wrong)
Vague memory of that too :)
I used to charge other kids at school to do that to their calculators.
I remember doing that as well, way back then
Yes, did this with calculators, too. There is also a certain clear packing tape that will actually make it colours, and even more colours if you put more layers
Do you have more info on this?
https://www.youtube.com/watch?v=eQudpY43hUc this video mentions “polarizing cellophane” tape, but I remember it working with a particularly-stinky clear packing tape
yeah, what’s old is new again apparently. first thing all us geeky kids did to them.
Yup, I remember that as well.
Isn’t there a whole Reddit dedicated to kids that do this?
Heh, indeed when I first saw the title I was thinking the same. How is this novel. Worse ‘a new polarizer, just flip it!!’. But the led. Hack is actually coiol. But why blue?! .. Red would be a better fit for dark mode.
Rotating the polarizer 90 degrees doesn’t work very well when the display is not square. Do some displays have 45° polarization direction originally, in which case flipping would work?
I assume it must be 45 degrees. I remember thinking at the time that it shouldn’t work, but did. (I was doing physics O level at the time, and understood polarisation as well at any time in my life.
You don’t need to change the placement angle, just flip it over
I did that when I was 14,: / that was on 1984. may be before, I Used to disassemble my watches to see what was inside.
Here is why inverted LCDs are harder to read: http://www.stefanv.com/watches/why-negative-lcds-are-so-hard-to-read.html
(TL;DR: You’re changing it from most of the screen passing light to most of the screen blocking light, so there’s less light available to come back through the active segments.)
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