mini lcd thermometer issue

Discussion in 'General Electronics Chat' started by xchcui, Aug 7, 2014.

  1. xchcui

    Thread Starter Member

    May 12, 2014
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    Hi.

    I bought simple mini digital lcd thermometer as in the attached photo.
    I accidentally,dismantle the thermometer,while the circuit board separate from the display glass.
    I reassamble it,but i am not sure if i did it right.
    Inside the thermometer there is a 2xlr44 battery that feed a circuit board which conduct current to the lcd display.
    The electrical connection between the circuit board to the glass display is by several contacts on one edge of the circuit board which pressed(when you close the thermometer box,it is not glue to it)on some kind of long,narrow,thin and elastic rectangular conductor that glue to the display glass(the display glass has also several contacts).
    When i tried to press the several circuit board contacts to the rectangular conductor,i found out that the there is a free play of 1-2 mm right or left that i can press the circuit board contacts on the rectangular.So here are the questions:
    is it matter how the several contacts of the circuit board sit on the rectangular elastic conductor?
    (i mean:does each contact of the circuit board should only sit at specific place along the rectangular conductor or the several contacts of the circuit board can sit anywhere along the rectangular conductor?

    Thanks in advance.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Those types of connectors are simply straight through vertical flexible connections with "sandwiches" of conductive foam between non-conductive foam
    1 "section/slice" per contact"
    I'd suspect you shouldn't have any problems.. If you do simply slide it to the side a bit.
     
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  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    The LCD has contacts that match the PCB. If you hold it to the light and look at the reflection you should be able to make it out.

    The thing between the display and the PCB is an Elastomeric connector (AKA a zebra connector) which is a flexible assembly of conductive and non conductive strips. Sometimes you can make out which is which. Wikipedia has mantion of it.

    Start out by centering the zebra piece, unless you can see some indication of where it was. You may have to play with it some, and it will not connect without some force applied.

    This piece is the typical failure point of a display.
     
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  4. xchcui

    Thread Starter Member

    May 12, 2014
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    There is another problem that i don't know if it is because of a bad fitting of the zebra connector and this is the main reason that i asked a bout that.
    After i reassamble the thermometer i could see the number(segments) on the screen pretty good,but when i look close on the display from aside i could see a very fast blinking of the segments(only the ones which are part of the number at that moment).when you look straight on the display,even close,you don't see any blinking,also not at ordinary look.

    Could it be that i put the PCB contacts on the zebra contacts in a wrong way,that current go from one PCB contact through the zebra connector to two display contacts(or similar situation) and caused the very fast blinking?
    My common sense say,that if i wouldn't put the zebra as it should:eek:r i would not see anything on the display or i would see on the display strange marks.
    What it could be?what could happens in wrong fitting?
     
    Last edited: Aug 11, 2014
  5. xchcui

    Thread Starter Member

    May 12, 2014
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    Anyone can help with that:(
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Could just be the refresh/sample rate of the display..
    Each blink is each time the display is clearing the screen and refreshing the reading.
     
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  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The blinking is more noticeable in some displays than others, but is common. If the display looks normal when viewed from the front then you have the zebra connector positioned correctly.
     
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  8. xchcui

    Thread Starter Member

    May 12, 2014
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    Why does a simple lcd display need refreshing?
    I know there is refreshing in in lcd tv screens but why in a simple thermometer?
    Is it to prevent,maybe,"image persistence"on the display?i mean to prevent the liquid crystals to stay"on" when the segment should be invisible?
    I was searching in the net and wikipedia with no success.
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    The display elements are constantly refreshes in every LCD display as the liquid crystal material itself cannot be subject to a DC voltage (why I don’t remember, it causes some sort of chemical reaction). So square waves are applied to the segments, either in phase or out of phase.
     
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  10. xchcui

    Thread Starter Member

    May 12, 2014
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    So,i see,that all the liquid crystal materials,with no exceptional,need to be refreshed.Now it is more clear.
    Thanks for your explanations.:)
     
  11. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I wouldn't call it "refresh" but "excited." These displays need an electric field to rotate the molecules to produce the polarization shift.

    Also, this field needs to be constantly reversed such that the DC content is zero.

    One could run a display on pure DC, though not for the long term.

    It's similar to a LED display in this way: you need to actively drive the LED to make a pixel or segment. I would not call that current a "refresh."


    I do admit I am being pedantic.
     
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