USB port to Serial pins

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1

I'm trying to get serial communication between a Pi and Arduino Mega but want to leave the Arduino USB port open for debugging. I'm about to go pick up a logic level converter to connect the Rx/Tx pins, but was wondering what would happen if I took a USB cable, plugged one end into the Pi (or PC or whatever), and stripped the wires on the other end and connected those straight to the Rx, Tx, and ground pins of the Arduino. Would the Pi and Arduino recognize each other?

2

No, USB and Arduino serial are different in both electrical characteristics and protocol. An intermediate device is required to convert from one to the other.

One workable approach would be to use a purpose-designed USB to TTL Serial Cable with the USB side plugged into a RPi USB port and the Tx/Rx/Gnd pins plugged into the appropriate Arduino headers. These cables have an active USB to Serial converter built into the cable.

3

Bapstack:
I'm trying to get serial communication between a Pi and Arduino Mega but want to leave the Arduino USB port open for debugging.

Perhaps use the SPI interface on the Mega and the PI:

MEGA: SPI - Arduino Reference
PI: Raspberry Pi Documentation - Raspberry Pi hardware

4

ReverseEMF:
Perhaps use the SPI interface on the Mega and the PI:

That would probably work, perhaps not as simply as Serial, but I would have the same issues with differing voltage levels. I ended up grabbing a usb to ttl cable, hoping that will do the trick.

5

Bapstack:
That would probably work, perhaps not as simply as Serial, but I would have the same issues with differing voltage levels. I ended up grabbing a usb to ttl cable, hoping that will do the trick.

Whoops, forgot the PI is 3.3V But, simple level shifters will take care of that:
[Search Results for 'level shifter' on Adafruit Industries](http://"Search Results for 'level' on Adafruit Industries shifter")
And, actually [me, wrong again] there are numerous USART ports on the MEGA, so your USB-to-TTL solution will likely work. Just avoid using Pins 0 & 1 as those are "used for communication with the computer" [Serial - Arduino Reference]

And, have you seen this discussion?: https://forum.arduino.cc/index.php?topic=435350.0