Reroute D3 to D0, add pullup on D0, swap polarity on one of the 12V harnesses (mostly just a label issue), add small cap between com and ground on driver chip (7-10nF).
Also consider adding a place for a rectifier diode on the master board 5V in, since the little buck converter lets current pass through to the in side of the board when powering from USB, which tries to power the motors.
Reroute D3 to D0, add pullup on D0, swap polarity on one of the 12V harnesses (mostly just a label issue), add small cap between com and ground on driver chip (7-10nF).
Also consider adding a place for a rectifier diode on the master board 5V in, since the little buck converter lets current pass through to the in side of the board when powering from USB, which tries to power the motors.