I'm thinking to make a programmable 2-axis plotter. Arduino would contain basic pre-programmed instructions with simple names (like "drawLine" would be "DL" and similar) and followed by some instructions like coordinates or length. For example draw a line would be:
1 SC "x" "y"
2 DL "x2" "y2"
were SC is "set cursor" and DL is draw a line from x y to x2 y2.
But my problem is that I don't know how to read from an SD card like I would read from a serial communication.
If someone can help me with a basic example I would appreciate it so much
There's an example on the Arduino Project Hub that I found via a simple Google search. It shows how to read from a text file stored on an SD card 1 character at a time and display it on a LCD.
It should be fairly simple to modify the example to process the characters.
About 1000 years ago (or so it seams now!) when I used to muck about with large format plotters, the language used to speak to them was called HPGL (Hewlett-Packard Graphics Language). It's a really simple text based language. Have a read about it on Wikipedia as it would save you having to invent your own language (unless you want to. There's also some HPGL viewers out there so you can visualise the results on screen as well.