A technical question on LCD operation
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Thread: A technical question on LCD operation

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  1. #1
    Member veracruz's Avatar
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    A technical question on LCD operation

    I've always read that LCDs work like electronic venetian blinds, letting light through or blocking it and thus producing various readouts on 7-segment or matrix displays. But I was just looking at my GLX-5500 from a very oblique angle, and I've noticed something I've never seen before: if you look from precisely the right angle, the two blinking dots (I've got a chronograph running) are not steadily blinking in a 1-second rhythm; instead, it looks as if there is a short energy peak (let's say 0.1s in duration) every time the dots light up AND when they disappear, i.e. twice per second. Furthermore, during the time when the dots are either on or off, you can't tell whether they're on or off from that particular angle, you just see those energy peaks when they change their state. The same goes for the segments that make up the seconds, the tenths are only noticeable when there is a change every ten seconds, and the hundredths display is very busy.

    I hope my explanation makes sense. And my question: is this consistent with a characteristic of LCD operation that is too technical to be included in those general explanations? What is actually going on?

  2. #2
    Member FROG's Avatar
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    Re: A technical question on LCD operation

    I'm assuming that what you're talking about is what appears to be bistable behavior of the blinking dots? That is, it appears to need a charge pump voltage to both polarize and depolarize?

    (This is causing an internal conflict because you know that LCDs are not bistable devices?)

  3. #3
    Moderator G-Shock Forum
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    Re: A technical question on LCD operation

    Since the peak is visible in both cases "power on" and "power off" i would assume an optical property of the liquid crystal itself is the reason.
    While "power on" could be done with a voltage peak, "power off" couldnt.

    Maybe someone in this forum has experience with LCD driver inner workings.


    Quote Originally Posted by FROG View Post
    I'm assuming that what you're talking about is what appears to be bistable behavior of the blinking dots? That is, it appears to need a charge pump voltage to both polarize and depolarize?

    (This is causing an internal conflict because you know that LCDs are not bistable devices?)
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  5. #4
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    Re: A technical question on LCD operation

    As others have mentioned, an LCD is not a bistable device, meaning that when the digits are turned on they don’t stay on. The TN/STN LCDs that are used in our watches typically use a refresh rate of 60Hz. Usually it’s difficult to see the refresh by the naked eye but I’ve noticed that it’s easier to see it in sunlight.

    The reason why you continually refresh a LCD at 60Hz is so that transitions from frame to frame or changing content will appear fast and clear. You wouldn’t want problems like crosstalk or slow transitions that you’d get with low refresh rates.

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    Re: A technical question on LCD operation

    In this video you see the side effects of multiplexing.


    Quote Originally Posted by zack20cb View Post
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  8. #7
    Member veracruz's Avatar
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    Re: A technical question on LCD operation

    Sincere thanks to everyone who has replied so far - I've certainly gained an insight that I didn't have before. As for the video, it seems to be showing quite an opposite effect, everything being very lively all of the time, while what I saw was very static, almost peaceful in comparison.

  9. #8
    Member FROG's Avatar
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    Re: A technical question on LCD operation

    Quite honestly, there's really no way to tell, but at the frequency you're talking about, my wild-a***-guessing is that it's a side effect of the LCD biasing charge pump.
    veracruz likes this.

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