Is it possible to have two arduino pro micro's and only have them ran by a single usb cable, like is it possible to do a master and slave connection but not plug the slave into the computer or the master? I don't mind having a power supply but I need two of these boards and only have room for one USB connection to come out (aviator cable).
Any help would be appreciated, thanks
Hi, @adamt2022
Welcome to the forum.
What is the application?
Why do you need two Pro Micros?
Thanks.. Tom.... 
You can put this in between:
Buy a usb break out and feed to 5v to the 5v pins on the two boards and 0v to both …
But as implied why two boards ?
I don't have enough pins on one board - I'm using 10 buttons and 6 rotary encoders for this project.
The application is for a steering wheel rim that only has space for one aviator connector to exit the base and I need two Pro Micros as there are not enough pins on the board as I'm using 10 buttons and 6 rotary encoders
As far as i understand connecting two USB devices directly to a single cable does not work, you need a USB-hub in between to handle the traffic.
For 10 buttons and 6 rotary encoders you should be able to use port expanders & shift registers etc to wire everything to a single micro-board.
If in the end you want to use two micros for the project with only one USB-cable going out to the computer, you can connect the two boards using the UART (Serial1) and handle board-to-board communication with that while the USB-connected board pipes all the data from the other board to the computer.
Despite its name a Universal Serial Bus, is not actually a bus. It can only deal with one device per connection.
Why do you expect them to make master-slave interchange if you don't want to plug slave anywhere?
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