Feedback on PCB Design

Projects General Guidance
1

Hello, I am looking to get some feedback on a PCB I have designed. I am currently designing a moving light that can be controlled through DMX. Essentially, I am using a Max485 chip to receive the DMX signal and send it to a Atmega328. I have two A4988 stepper motor drives to control two stepper motors and the LED will be made using NeoPixels. I am using a 15V power supply to power the motor drivers and a 5V power supply for everything else. I also have a relay to make sure the 5V is turned on before the 15V. Below is a picture of the schematic I have created.

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I have tested this circuit and created a PCB using the schematic.

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I have never designed a PCB before, so if anyone could give me some feedback, such as trace width and spacing, or if anything looks obviously wrong, it would be much appreciated.

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Schematic is very low resolution :woozy_face:

  • Try to move blue traces to the red side.

  • You have not connected anything to the controller Reset pin ?

  • How will you be programming the controller ?

  • Add ground pour

  • Where is Vcc connected to 5v ? :thinking:

  • Your + - silkscreen on the 5v terminal looks reversed

3

I have no real experience of this and have yet to receive my PCBs, so the following may be mostly rambling rubbish.

It looks like your PCB has been prepared in KiCAD. If you have done it all exactly according to the book, there is guidance about adding pours "zones". If you have done the real work by other means and merely used KiCAD for the actual tracks and pads, I don't think you can simply add the pours, you have to make them up yourself. I didn't bother.

There is/was a tradition of component side (front) and solder side (back). I don't know if it applies so much these days, but I stick to it. If it's KiCad, blue is on the back and red on the front and so, contrary to what Larry said, I would move red traces to blue wherever I can, the logic being that the solder side is where the tracks go.

Now I don't know if the pads can be used as vias and it doesn't actually matter which side you apply solder but, since they provide vias, I assume it is a good idea to use them and I took this to mean that red tracks never go to a pad, they change to a via nearby so that all soldering is strictly on the solder side. This ensures that there is no such thing as a hidden pad.

I guess your controller is in a socket and can be re-programmed back in the Uno. I am using a ProMini soldered-in and have provided a pinrow for on-board programming. This may not be practical in your case - or warranted.

I don't know if it is still bad practice to have acute angles where track meets pad etc., but it is still a bad look, and you have some between the switchbank and the controller.

As far as track width is concerned, if you look at the tables, i think it is clear that the default 0.25mm covers pretty well everything and is the default for good reason, and then you do the bleeding obvious and fatten up power and ground to 0.5 and 1.0mm and keep them short - just like plumbing. I found that KiCAD is not above changing some track to 0.2mm when I wasn't looking. There was some other flakey things going on as well, but I will put some of that down to me.

I found the KiCAD forum pretty good. It comes off the same drawing board as this one.

I post this because i am asking as much as telling!

4

Sorry about the low resolution, hopefully, this is better.
Schematic.pdf (93.4 KB)

To address some of your questions and some of my own questions:

  • Just curious, is there a reason all the traces should be on one side because it's going to be a bit difficult to do?
  • I may connect a button to the controller reset pin, but probably not.
  • The controller will be programmed outside of the PCB, I'm going to use a DIP socket so it can be easily removed and put back in
  • Is it good practice to use a ground pour, or is it not always needed.
  • The VCC is the 15V, so that's why they're not connected
  • The + and - for the 5V terminal was reversed, thank you!
5

Yes I did use KiCAD, what's the benefit of using pour zones? I know it's often used for ground planes, but is it just to make it easier to route?

Is there a downside that you know of to have traces on both sides?

I will definitely check it out, thank you!

6

  • Just curious, is there a reason all the traces should be on one side because it's going to be a bit difficult to do?
    That way you can have the bottom free for a GND pour.
    Do your best, avoid long traces in ground pour, use strapping over cross unders.
    image

  • I may connect a button to the controller reset pin, but probably not.
    Connect Reset to 5v through a 10k resistor.

  • Is it good practice to use a ground pour, or is it not always needed.
    Placing a ground pour on the bottom reduce switching noise on traces.

  • The VCC is the 15V, so that's why they're not connected
    Don’t see the Vcc to 15v connection in the schematic.

7

I believe that, when boards were etched, it meant less heavy metal compounds going down the drain. I don't think that applies so much these days.

It also means that the tracks for ground (and power) have the current density minimised as much as possible.

It has no bearing on routing, indeed quite the opposite.

Definitely not. Double sided is the norm and keeping tracks to one side only could easily cost you more, and would certainly suggest you don't know what you are doing. Indeed, about the only reason I can actually think of for having the traces on one side only is where you need the other side as a copper RF shield - still double sided... I don't know what your project actually does, and there could be more need for pours.

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@LarryD @Nick_Pyner Thank you both for the feedback, I really appreciate it!

9

I would suggest using a different stepper driver like a TMC2209. The A4988 is VERY noisy. I don't know what your planned application is but if it's not for a night club you're going to be annoyed by the A4988.

1 Like
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I did notice it is quite noisy. I don't really have any planned application for it, but I will look into it, thanks.

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Not sure if I did it correct, but that was actually quite easy.

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:+1:

I have not checked everything.

13

Further to my first, my boards arrived this afternoon. Now that I have one in my hand, it seems pretty clear that the pads can be used as vias in the manner that you have done it.

I can't get over how well-made these boards are, and they arrived a day earlier than the minimum time quoted.

JLCPCB

1 Like
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That's who I plan to use. Glad to hear your boards came out good

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