Simple Hack Creates An Inverted Watch Display

Before and after of a negative display watch conversion

Sometimes you have to bust out the wayback machine to find a good hack. Back in 2008, [Brian] performed this awesome negative display hack on his classic Casio G-Shock watch. The G-Shock, like most digital watches, uses a twisted nematic LCD. All Liquid Crystal Displays are made up of a layer cake of polarizers, glass, and liquid crystal. In non touchscreen displays, the top layer is a sheet of polarizing film glued down with an optical quality adhesive.

[Brian] disassembled his watch to reveal the LCD panel. Removing the glued down polarizing film can be a difficult task. Pull too hard and the thin glass layers will crack, rendering the display useless. After some patient work with an X-acto knife [Brian] was able to remove the film.

Much like the privacy monitor hack, the naked watch appeared to be off. Holding a sheet of linear polarizing film between the watch and the viewer reveals the time. If the film is rotated 90 degrees, the entire screen is color inverted. [Brian] liked the aesthetics of the inverted screen, so he glued down his polarizing film in the offset position. After reassembly, [Brian’s] “customized” watch was ready to wear.

[Via Hacker News]

42 thoughts on “Simple Hack Creates An Inverted Watch Display

      1. I remember doing just that in middle school to impress the girls. I also made and brought a few LED flashlights (they were a big deal back then) and most proudly of all, I stumped the science teacher with a small flyback converter lighting a neon bulb with only one wire.

      2. Where did you get the polarizing film from? I mean, even if the film wasn’t glued to the display itself like they usually are nowadays, you have to turn it 90 degrees so you can’t use the existing film.

  1. I remember doing this when I was in elementary school; I took apart the class calculator and the polarizers were loose sheets floating around. So as they fell out and I went to put them back in I discovered this. A couple years later when I was taping a display down with packing tape I noticed it created colours! And layering the tape created yet more different colours. So I ended up stair-stepping the display with tape so each segment was its own colour.

    1. Hey, I used to do this to calculators in elementary school, too! Odd that there seem to be so many of us. Maybe tinkering with things at that impressionable young age is what led us here all these years later.

        1. I have seen leds in calculators before too, now that I think about it. Not intended to be visible. Little white bodied ones with a drop of red resin on the top. I wonder what they were for? Did they need a larger voltage drop diode than standard? Maybe use it as some sort of regulator with the solar cell?

    2. I couldn’t do the polarizing trick with my favourite calculator I used at school, because it had a VFD display, a Casio M1. Still got a couple of those and a few other ‘vintage’ calculators I bought from car boot sales including a couple of Sinclair ones.

    3. Talking of (something like) this, what’s the name for those multi-coloured LCDs? The ones some calculators and old personal organisers use, they do blue, green, and orange. There’s no RGB splitter thingy, the LCD itself produces the colours, no backlight.

      I spent ages looking it up, found out, then forgot again. I also wonder if they still make or sell them?

    1. Spy watch, cool. Or take the polarizer out of your calculator and use it during a math test! Quick, somebody get me a time machine, I gotta send a message to my past self.

  2. Or, you can salvage the pieces of polarizing material (from a pair of cheap sunglasses works better) and place any transparent material between them: quartz, plastic, small rocks…place a light source underneath and see the structure and stresses in your sample as you rotate the top polariser.

    I learned about this when I built a polarizing microscope from a Bell Labs science kit inhigh school.

    1. You can buy the polarising sheets from educational suppliers online, they’re not too expensive. Depends how “educational” the site is, places that do the full hand-holding for ignorant teachers charge more. Same thing applies in computing actually. Hobby / geek suppliers are cheaper.

  3. Funny, did the same to the digital displays in my late 80’s volkswagen.
    Black letters with backlighted background is a royal PITA at night.
    Flipped the inverting film, and now only the letters are backlighted while the background is pitch black

  4. I did that to my brother’s calculator back when we were in school back in the 80s, he wasn’t happy!

    In my collection of over 40 wristwatch games I have no-brand one called Frog which you have to jump between lilypads, it still has the protective film on the front so hasn’t been used and I can understand why – when they made it they glued the polarizing layer on backwards, inverting the display and making it unplayable.

    1. Oooh, 40 wristwatch games! You dunno how jealous I am! I’ve collected and lost a few over the years, and got a few for xmas way back when. Tiger’s Batman kept me sane through a series of insane detentions at school. And after years I managed to buy, from Ebay, a second Tetris watch, which is the king of game watches and the only one you really need. Til they bring out one with Freecell.

  5. There’s a process on the original gameboy that some people have taken to calling “biverting” that uses this to increase the contrast.

    First step is do what’s here, rotate the polarizer to invert the display. For reasons having to do with the optics of liquid crystal, that increases the contrast (default dark segments are darker than ones that are dark due to electric field)

    Other step is to add a 74hc04 to invert the logical sense of the signals used to drive the LCD, re-inverting the appearance. Twice inverted = “biverted”, apparently. End result: higher contrast, and screen that’s black when off. More useful if you also add a backlight.

    1. Strange thing is that every LCD monitor I have taken apart has a LCD that would be full white if you powered up the backlight by itself. Is there a reason they don’t have it default to black and power the pixels to make them go white if that improves the contrast ratio?

  6. These G-Shocks are great watches and more hackable than most. Not mentioned in the HAD summary is that this watch has been further “stealthed” by removing the white paint on the outer bezel. The bezel can be dyed as well, the whole watch can be torn down and repaired, etc. All of this is documented in this wiki.

    I recently picked up the newer version, pre-stealthed version of this watch off an EBay seller in the UK: the 5610BC-1ER. This watch has a properly adjustable stainless steel, resin-coated band rather than the all resin band that comes with those watches with black-on-white displays (a must for my skinny wrist). This watch is pretty much perfect for me: no battery to worry about, syncs nightly to an atomic clock, is not made overly large with other features that only half work, etc. And it looks very, very cool.

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