Serial connection garbled characters

Issue: When connected via serial to my device, I can see only garbled output and strange characters in putty.

Example:

my▒--!#▒▒▒▒▒▒▒▒▒▒▒▒R▒▒럣▒▒▒▒▒▒E▒#7!%▒▒9▒-#-▒7!#5▒▒H▒▒▒▒▒▒▒E▒#7!%▒▒▒▒#7!%▒=▒▒▒%-57▒75▒!▒5'-%--#1▒▒R
▒▒띣▒▒▒▒▒▒E▒%▒▒A%=9▒▒▒▒▒▒▒▒▒▒%=9▒▒s-▒S5▒▒▒▒▒▒▒▒▒▒▒ ▒▒▒띣▒▒▒▒▒▒E▒%▒▒A%=9▒▒▒▒▒▒▒▒▒▒%=9▒▒{-'7▒W-%5▒▒▒▒▒
▒▒▒▒▒▒▒▒▒▒▒▒▒R▒▒띣▒▒▒▒▒▒E▒%▒▒A%=9▒▒▒▒▒▒▒▒▒▒▒R▒▒뛣▒▒▒▒▒▒E▒)%!7'!=75▒7!#5▒'!=7-#1▒)5'▒%!7'5▒3▒59▒%!7'5
▒7▒▒▒▒R▒▒۟▒▒▒▒▒▒▒E▒;'=#▒▒!▒▒5/▒▒▒▒▒5#57▒;'!9)-#1▒=5▒▒R▒▒۟▒▒▒▒▒▒▒E▒;'=#▒▒!▒▒5/▒▒▒▒▒5#57▒7-=;'57▒=5▒▒R▒▒۟
▒▒▒▒▒▒▒E▒75-95▒5/▒▒▒▒5#57▒!▒%!75▒▒▒▒▒▒▒▒▒E▒75-95▒5▒▒5#57▒!▒%!75▒▒R▒▒۝▒▒▒▒▒▒▒▒▒R▒▒۝▒▒▒▒▒▒▒E▒m_▒▒▒}ww[
yacs▒cuWwuSAyo}cqu▒▒▒;'=#▒▒'-#)▒;59!%5▒=7▒5#57▒3!-#1▒=5▒▒R▒▒۝▒▒▒▒▒▒▒E▒m_▒▒▒}ww[yacs▒cuWwuSAU_▒▒▒;'=#

Root causes:

1. Faulty GND connection
2. Faulty other connection
3. Wrong serial connection settings (e.g. wrong speed)
4. Wrong voltage level (e.g. 5V i/o 3.3V)

Solutions:

1. Make sure your connections are right, e.g. properly soldered.
2. Try different settings, e.g. all speeds from 9600 up to 115200
3. Use serial adapter with correct voltage level for your device

Links:

• Serial port troubleshooting