Issues realted to Communication Ports
/dev/ttyAMA0 -> Bluetooth
/dev/ttyS0 -> GPIO serial port.
Pi3 UART stopped working? Read this.
https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=141195
Overlay to remap Pi 3 UART
https://www.raspberrypi.org/forums/viewtopic.php?f=107&t=138223
Raspberry Pi 3 compatibility (BT disable & serial port remap fix)
https://openenergymonitor.org/emon/node/12311
ttyS0 belong to 'dialout' group
Find what groups the user belongs to
groups ${USER}
**Add user to 'dialout' group
sudo gpasswd --add ${USER} dialout
