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[Reply #15 on:]

A single 12V supply is the way to go, if you are happy with the solenoid getting 12V and the stepper motor about 10V (because the L298N drops about 2V). You can feed the Arduino directly from that 12V supply into the barrel jack or the Vin pin, unless you are drawing a lot of extra current form the +5V line. No need for a separate regulator.

As has already been pointed out, the diode in the mosfet/solenoid circuit is in the wrong place and does not protect the mosfet.

You also need 8 diodes connected between the L298N outputs and the ground and +12V supplies. See the L298N datasheet for details.

If you need to reduce the solenoid voltage, the simplest way is just to put a power resistor in series with it.

[Reply #16 on:]

Great advice DC!

I will do just that.

I guess i will need schottky diodes since im working with ~1amp on the motors? i didn't know about the 2V drop! thanks for the help

[Reply #17 on:]

No, 1N400x diodes will be fine. The stepper motors take less than 400mA @ 12V and the diodes only conduct briefly when a phase is turned off. It's when you control DC motors using PWM that the diodes can end up conducting for a large part of the cycle.