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LCD drivers

Discussion in 'Electronic Design' started by Howard Delman, Sep 30, 2005.

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  1. I am considering using an MCU that has built in LCD drivers, but it only
    implements 1:8 multiplexing. In other words, it has eight "common"
    lines that are sequentially asserted. I need to connect it to an eight
    character seven segment display. None of the displays that I have found
    are designed for 1:8 multiplexing. Is it possible, and reasonable, to
    use this MCU with a display that only has four commons (1:4
    multiplexing)? If so, would I use four consecutive commons, or every
    other one? Would the appearance suffer in any way? And what if the
    display is 1:3?

    Thanks for any help.
    Howard Delman
  2. Donald

    Donald Guest

    Of the CPUs that I've seen, they can be programmed for 1:1, 1:2, 1:4,
    and 1:8.

    It would really help us help you if you would just tell us what you are
    using, instead of letting us guess.
  3. I am considering the Elan EM78869. It only allows 1:8 or 1:9. It has
    more than enough segment drivers.

    I've designed a handful of products with LCDs, and I know well how to
    use them. What I have no experience with is using an LCD with a
    mis-matched driver. I am hoping that someone on this list does.

  4. Donald

    Donald Guest

    I found this:

    I would guess that this chip was designed for a specific customer
    before it was released to the public. Which means the specific customer
    had a specific LCD display they were using.

    As you seem to well know, LCD glass is brain dead simple. All the
    work is done in the LCD controller. So, I think you need to find a 8 or
    9 common LCD display.

    I wonder if this would make the display fab cheaper than say a 4:1.
  5. Thanks for the link, but I already have all of the information on the
    processor. In fact, I have been in contact with an FAE at Elan in
    China. What I don't have is a good answer to my question. The Elan FAE
    recommends that I buy their emulator, build it, and try it, but I don't
    have the time. I am bidding on a contract, and I really need to nail
    down my processor before I can submit the bid. This is a high volume,
    low cost, consumer product, in which a few pennies is a significant
    amount. Otherwise, I would just go with a custom display to match the
    processor. Low price is what makes the Elan processor so attractive.

  6. I don't think it will work acceptably unless you can source a matching
    LCD display.

    Do some calculations of the RMS segment voltage in each case and
    compare for yourself.

    Best regards,
    Spehro Pefhany
  7. Donald

    Donald Guest

    I whole heartly agree here.

    If the volume is really that high, the limiting cost would be the long
    lead items. And I bet its the LCD.

    Time is also money, We all know the curve, the later the delivery the
    later the tapping of the market share and lost revenue.

    Something I keep lossing track of " KIS " ; keep it simple.

  8. Thanks for the help, guys. I suspect you are both right.

    In this case, time is more than just money. It could be the entire
    contract. If I don't submit this within a week, it won't happen at all.
    That's why I can't get the emulator from China and try it out.

  9. I read in that Howard Delman
    How much to get it air-couriered from China? Quite a bit, no doubt, but
    as a percentage of the contract?
  10. It not just shipping time. This is not like dealing with I
    can't just pick up the phone and have one sent the next day. It would
    take a couple of weeks to get the order through the system, get the
    funds wired to Hong Kong, clear customs, etc. And then I have to get
    the system installed here, learn how to use it, etc.

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