This circuit uses two hybrid stepper motors each connected to a stepper motor driver A4988 and powered by 9 V DC supply to the drivers' MV pins. Both motor drivers have their VDD (logic supply) pins connected to the 5 V output pin from an Arduino UNO R3.The hybrid stepper motor used has a rated current (Amps/Phase): 1.68 and a recommended voltage: 12 - 24 V.
This is the circuit schematic relating to the stepper motors and drivers:
Why is there a 35 V decoupling capacitor? I understand the reasons for using a decoupling capacitor but why this particular value of 35 V? The power supplied to each A4988 motor driver to drive the stepper motors is only 9 V DC. So, why not use a 10 V decoupling capacitor? Or a 50 V for that matter? I did some research and found on some posts that some people are saying that it is a good rule of thumb to use a decoupling capacitor twice the value of the input voltage, to protect the motor driver against voltage spikes. If that's true, then the correct decoupling capacitor would be 9 V x 2 = 18 V? Actually, i'm not sure but maybe there is a mistake on that schematic if it's using 35 V. Any suggestion or advice would be highly appreciated.