Save Data from Arduino to .txt with Processing

Processing Electronics (Arduino, etc.)
4

again you try to save to file ?something?
in every draw loop ( 60 times per second )
without knowing that / what data have arrived.

only save to file if new data.

so move the

output.println(val);

out of draw and into serialEvent after

val = rx;

also that is the moment where you should print “val” content to console
so you see that/what data have arrived.

optional:
the concept to export to file with a header line
sounds more like you want/need to make a CSV file
so you should store the data into a
https://processing.org/reference/Table.html
and only on command ( keyboard?) do a onetime
https://processing.org/reference/saveTable_.html

and also this makes it possible to use the data ( from table ) inside the sketch
to draw something with it.

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