Calculator LCD Display

[djlorenz]

hi guys, i have i nice topic to talk about....

i wanna work with a calculator display, no matter if casio or sharp.. but i wanna use a "standard" scientific calculator with dot display line... not segment and i wanna control it.
i know that lcds have not controller on it, my casio (fx-350MS) has only one big chip, probably fpga with everything inside it...
and i know this displays have a special "ac" modulation...

is possible to use pic with built in LCD control, the microchip AY0438 or a standard HD44780 with them?
does somebody know how this display works and wich pinout? my casio doesn't have any model or brand on the display

i think this should be a nice topic to talk...
ciao
Lorenzo

[mariush]

There are ready made dot matrix lcd screens you can buy, which have a controller (similar to hd44780) on the back side, so you can control them using i2c or spi or just bit banging them through several wires.

See

* http://www.newhavendisplay.com/lcd-graphic-c-21.html

* http://www.digikey.com/product-search/en/optoelectronics/display-modules-lcd-oled-graphic/524918

* http://uk.farnell.com/graphic
* http://uk.farnell.com/displays-oled

* http://uk.rs-online.com/web/c/displays-optoelectronics/displays-industrial-monitors/lcd-monochrome-displays/  (choose display type : graphic)



There's also mouser.com and ebay also has cheap graphical lcds (but quality on cheap chinese displays can vary, they're ok for home projects but not recommended for production)

[djlorenz]

yes maurish, i know that, but the project we wanna do needs the calculator and it's own display!

this is why i need to  myself

[mariush]

Then get yourself a signal analyzer (bus pirate, whatever) and sniff the communication between the chip and the lcd.

If it's dot matrix, it's most likely there's a chip-on-glass type controller that converts whatever comes from the calculator cpu to the display.

Otherwise, if it's raw screen, then you have several common pins and lots of segments that are multiplexed, so you have an ac voltage of various levels going through the segments

Search for application notes about lcd displays, you'll find info about it.

[djlorenz]

yeah, i just found this:

http://www.ti.com/lit/an/slaa516a/slaa516a.pdf

the inside part of the calculator is shown in attachment, i think there is no chip on glass but all directly to the main chip 

[glatocha]

The Chip will be kind of ASIC made in 100000 pieces.
The LCD most probably will be custom made with special symbols, menu or whatever the calc is using.
LCD will be segmented (a segment can be part of a digit, text, symbol etc.). We don't know how many segments are there, maybe you can count it.
Then if you count number of lines you will know how many common lines are there.

Then you will need to find which pins are common. Then chose the correct uC with LCD for appropriate number of segments and common lines (Dave bloged about this).

I think, all of this is possible. But the effort and time? It would be kind of just prove that you can do it.