Question about rerouting calculator

Discussion in 'The Projects Forum' started by atikot, Jul 15, 2011.

  1. atikot

    Thread Starter New Member

    Jul 15, 2011
    3
    0
    hi, i'm working on some project and i need to reroute a calculator (i have casio fx-82ms and a chinese copy of it (which is really different from the inside)) i would like to connect the key's and display to my own micro-controller , the problem is the display , the connection has very small wiring so i can't connect it by hand and i can't develop a board with such small wiring for the screen, the screen size is 64x21 (couldn't find such screens on the net) is there a chance to find same screen but with more simple connection? is there any other way to bypass this problem?

    can any one suggest a solution?
    thanks.
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,392
    1,606
    Sorry, no real way to get around this. Typically there is a rubber membrane between the glass and the PCB to route the fine traces on the glass (thin gold you can't see) to the PCB.

    Even if you connect those, and figure out which pin drives which segment, you still have to drive the thing with exact square waves (in phase for off, out of phase for on). If you have any imbalance you generate a DC and the "L" stuff goes bad.

    Have I scared you off yet? If not I can think of a few more reasons not to do this, like if you actually come up with a product you will have to buy Chinese calculators and cut them apart.

    (Reminds me of the time I found several hundred RC controlled model Mini Coopers in the dumpster at work. Company next door found it cheaper to remove from existing model then buy a basic controller. But I digress...)

    There are many fantastic displays out there for cheap. If you just want a line or 4 of 8 or 16 or 20 characters that's there. If you want a blue & white 128x64 graphic display they exist too.

    I'm playing with a 320x240 color touch screen display here and they are cheap and fantastic.

    You may have better luck hacking out the keyboard, depends on how it is made.
     
  3. atikot

    Thread Starter New Member

    Jul 15, 2011
    3
    0
    thanks for the answer,

    i'm not planning to sell or produce a big amount so it doesn't really matters if i use the Chinese calculator or not, the idea is to reroute the calculator so that visually it will look the same. if i could find lcd screen that will look and fit to the calculator that should do, the trouble is i can't find one.
    maybe you know any standard scientific calculator i can buy exact lcd screen that doesn't have this complicated wiring?

    closest i could find, and yet the size is not exact so it won't fit perefectly
    http://il.rsdelivers.com/product/di.../16x2-reflective-cog-stn-yel-grn/5326559.aspx
     
  4. atikot

    Thread Starter New Member

    Jul 15, 2011
    3
    0
    what if i would connect the calculator wires going to the screen to a logic analyzer could i get the exact square waves i need to send to the screen and then send the same waves with my controller?
     
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