How to activate /dev/ttyS0 on Raspberry Pi
1. Disable tty console (ask google, or use raspi-config)
2. Add pi to dialout group
sudo usermod -a -G dialout pi
3. Make link to ttyACM0
cd /dev sudo ln ttyAMA0 ttyS0
4. Optional: Install terminals
sudo apt-get install minicom cutecom