I am building a circuit with 2 hybrid stepper motors each powered by a stepper motor driver A4988 and both drivers are connected to an Arduino UNO R3.
Before soldering the components together on a PCB, I would like to clear my doubts, confirm what I'm doing and prevent any disasters or improve it, if possible.
I have done some research about the importance of using capacitors, but I still have some unanswered questions.
Here are the specs for each hybrid stepper motor:
Rated current (Amps/Phase): 1.68
Recommended voltage: 12 - 24 V
Holding torque (kg.cm): 4.4
Resistance (Ohms/Phase): 1.65
Inductance (mH/Phase): 3.6
Here are two variants of the section of the circuit schematic relating to the stepper motors and drivers:
I have a few questions since during the circuit design, I've been puzzling over several aspects of the decoupling capacitor placements and their respective capacitance and voltage ratings.
I have made two versions of the schematic in the picture above but I can't figure out which one is better. And why? In design B, I have placed a 100nF ceramic capacitor between the 5V and GND of each stepper driver - is it better from a design perspective? Although design B uses one extra 100nF capacitor compared to design A, I am trying to make the best practical circuit possible and explain it coherently.
Why connect a 35 V electrolytic capacitor when only a 9V supply is used to power the motors? How is this 35 V calculated? I found this in a schematic during my search but I want to understand why that value was chosen before i build it.
I have read that as a good rule of thumb to always use a small 100nF ceramic capacitor and a bigger 100uF electrolytic capacitor in parallel to the supply and ground. But in this schematic, there is only a 100 uF between the MV and GND, so should I add a 100nF ceramic capacitor in parallel to improve this design??
Why is a 100nF ceramic capacitor used between the logic voltage 5V (supplied from the 5V output from the Arduino UNO R3) and GND? I read that it filters out high frequency signals. But shouldn't the voltage output from the 5 V pin on the Arduino already be stable??
The recommended voltage for the motor is 12 V, so if I were to use a 12 V DC power supply instead of 9 V, what capacitor voltage ratings should i use? How do I calculate this?
I have set the current limit to each stepper motor to about 500 mA (from my online search, I read that a limit of 500 mA is safe so as not to damage the wires,) so is that something to be considered when choosing the capacitor ratings?
At this point, I am just blindly using what I found in my search online going through several schematics without really understanding why. I would really appreciate some clarifications. Maybe someone with PCB design experience can enlighten me on these issues.