Bash comm. with arduino uno over ttyACMx

i found a screen package for dreambox
when i enter screen -e '1' > /dev/ttyACM0

i get exactly the same result. The led flicker a few times and thats it.

and found a picocom package for the box.
with picocom -b 9600 /dev/ttyACM0 i can set the led correctly! -great!!!!

how can i kill the terminal ?Once i have open picocom i cant stop?

Any idea because it dosnt work the usual way with echo?
thanks