Hello, I have recently designed my first ever PCB, which looks like this (on the back layer there is a copper pour which joins all the GND pins):
The circuit is a very simple stepper motor controller that features an arduino Nano, a A4988 stepper motor driver, 3 buttons to perform various actions, 2 LEDs for signaling the different operation modes of the motor, a fan attachment and two connectors for an external buck converter to switch from 12V (power in) to 9V (which I use to power the arduino via the "Vin" pin).
As you can see, I have included two slots where I can add two capacitors (C1 and C2), one in parallel to the "Vmot" and "GND" pins of the A4988 (which will receive 12 V in), and one in parallel to the "Vin" and "GND" pins of the Nano (which will receive 9V in).
Now... What type and value of capacitors should I use for each? And more importantly, could you please explain to me why you would choose a particular capacitor over another, so that I can figure it out for myself in the future?
Finally, if you feel like, could you tell me if you think the PCB seems okay, or if it has some obvious problems?
Thank you so much!