If you're working with Arduino, you may already have a UART cable handy. You can use that to interface with the Pi via the serial pins.
Any cheap UART interface will do for the purpose. I personally use a $1 CP2102 clone that I got from eBay, directly wired into the Pi's serial pins.
Once you're connected, simply use Putty in in Serial mode, enter the COM port number (e.g.
COM3), set baudrate to 115200, and you're good to go.
You can read more about the serial interface here: https://elinux.org/RPi_Serial_Connection
The serial port is a low-level way to send data between the Raspberry
Pi and another computer system. There are two main ways in which it
can be used:
- Connecting to a PC to allow access to the Linux console. This can help
to fix problems during boot, or to log in to the Raspberry Pi if the
video and network are not available.
- Connecting to a microcontroller
or other peripheral which has a serial interface. This can be useful
if you want the Raspberry Pi to control another device.
I have heard that the serial interface on the Pi 3 may have problems (something to do with Bluetooth), but I haven't encountered it in recent times. It may have already been fixed.