First, check your /dev/ttyS0 or /dev/ttyS0

> stty -F /dev/ttyS0
speed 9600 baud; line = 0;
min = 0; time = 10;
-brkint -icrnl -imaxbel
-opost -onlcr
-isig -icanon -iexten -echo

if not

> stty -F /dev/ttyS0 -icrnl -opost -onlcr -isig -icanon -iexten -echo

> ./Linux_DBG_FLOAT/onoff 0