I have an LN298 I'm using to drive a NEMA 17 stepper motor which is powered by a 12V/29A supply. I'm planning to use the LN298 5V output to power a NANO that will also provide the control input to the LN298. The stepper motor is being used for a syringe pump and will be used in occasional short movements, so there will be very little power consumption. I also have a protoboard with a 5V power rail and a ground rail between the LN298 and the NANO. The protoboard will have input for two buttons to manually move the syringe pump backwards and forward, and will have two reed sensors acting as limit switches. I'm using 1Kohm pull-down resistors for the switches. Finally, I'll be triggering the syringe pump with a high signal coming from a MEGA that probably won't have a common ground and be powered by a USB. Here's an schematic of my planned set-up:
Beyond a general check from anyone who'd like to share input on my design, I have a few questions:
Will a 1Kohm resistors be fine here or should I use a larger resistance? Also, what's the smallest wattage resistor I can use in this situation? How do you figure these things?
Do I need diodes on my ground between the protoboard and the 12V supply and LN298?
I will have four of these (schematic) setup as individual modules with their own 12V power supplies. My question here is will the MEGA need to share a ground with all of the modules or be fine not sharing a ground.
Bonus question: I left this out because I thought it would make the above too complicated but each individual module circuit will also have three BTS7960 motor drivers controlled by three respective NANOs. The NANOs will be powered by a 12V to 5V DC buck converter in this case. My question here is will my ground be ok between all these devises? Do I need diodes anywhere there's a motor driver and a shared ground? If so how do I figure out what kind of diodes to use? Finally the MEGA that isn't sharing a ground and powered by a USB will be signalling all of these guys with a HIGH signal. Will the MEGA not sharing a ground be ok?