can i read an existing lcd from arduino

is there a way to read from a arduino the signals going to a standard 20 x 4 lcd display from a seperate controller that cannot be modified ! on a arduino that i can see the data to work with... I have a controller on a machine that i cannot change code on but need the % completed number from the display so i can display it on a LED display seperate . is there a library to do that ? or where would i start ? i have the display pinout its the same as the lcd in our kits.

bst056981:
is there a library to do that ?

Doubtful

or where would i start ?

With the datasheet of said LCD.

i have the display pinout its the same as the lcd in our kits.

If it works with the HD44780 drivers (most Arduino compatible LCDs do), then you can look into the LiquidCrystal library to see how it sends the commands.

I have a controller on a machine that i cannot change code on but need the % completed number from the display so i can display it on a LED display seperate

That's a really strange condition. Care to elaborate?

bst056981:
i have the display pinout its the same as the lcd in our kits.

I wasn't aware you and I were sharing a kit. (What kit?)