ATmega32U4 Development board design

[spencerlommel1]

This is my first time doing PCB/schematic design with a microcontroller. I am making a development board based on the ATmega32U4.

I think my schematic is all correct and ready to start PCB design but I had a few questions if anyone could help out.

• Is my oscillator (Y1) capacitor placement correct? and do these need to run to UGND like I have here?
• I have a sort of separated 5v line. Before and after the ferrite bead. for any MCU related stuff I try and pull from the 5v after the ferrite bead is this correct?
• Should I have a separated GND for my MCU similar to how I have a separated 5v?
• Is my 3.3v test pad (TP1) in the correct place?

If anyone notices any other issues with my schematic please let me know!

I greatly appreciate any help.
Spencer

[jim-p]

Your schematic would look a lot less chaotic if you use the GND and power symbols

[spencerlommel1]

Do you mean I should have multiple of these GND symbols throughout my schematic? Like should I put one to the left of that capacitor at C11?

[BitSeeker]

Don't think that 0.1uF should be connected to xtal?

[spencerlommel1]

@BitSeeker I think you're right!

I did some research and it looks like you would usually connect AREF to an external 3.3v for analog reference. I don't think I'll use analog so should I just leave it like this?

Or is there a better solution where I can easily connect this? Would it be fine to route the 3.3v from UCAP up to this AREF or is that not stable enough?

Option 1

Option 2

I think Option 2 would be better I just don't know if this is supported or if I should connect somewhere else. The main goal of this board is just a simple board to teach myself schematic design so I don't really need analog features

[spencerlommel1]

Thank you everyone for the suggestions so far!

I took some advice from here and other places and made the following changes

• Started using nets more and made colored nets (I could probably still use more nets for those long traces)
• Fixed some issues with my oscillator caps
• Removed connection to AREF and left it floating (https://electronics.stackexchange.com/questions/195233/aref-on-atmega328-if-analog-is-not-used)
• I'm not sure if I'll ever use it but I decided to break out AREF and another GND pin for development.

If anyone sees any other changes I should make before I start PCB design please let me know!!

[belmont1591]

Hi,

Please consider making the connections this way. Remember that you can change the pin position of any symbol (the schematic is not complete.)

[GolamMostafa]

@spencerlommel1

If anyone sees any other changes I should make before I start PCB design please let me know!!

Before you make the PCB, prototype the system in veroboard and check that the system works to meet your requirements. See below my approach to build an ATmega328P Based (a colone of Arduino UNO) system:

You may also study the schematic of the following ATmega32U4 System to judge/vaildate your design.

[Deva_Rishi]

@spencerlommel1

Is my oscillator (Y1) capacitor placement correct?

Within the schematic yes, but their physical placement on the PCB is also relevant.

@GolamMostafa

Before you make the PCB, prototype the system in veroboard and check that the system works to meet your requirements

Now there's a good plan !

[jim-p]

@spencerlommel1

Do you mean I should have multiple of these GND symbols throughout my schematic?

Yes.
I circled C11 for a reason. Do you see your mistake?

[jim-p]

@spencerlommel1

If anyone sees any other changes I should make before I start PCB design please let me know!!

What happened to the cap on Aref (C11)?
Use the GND symbol as I already recommended.

[Deva_Rishi]

@jim-p

What happened to the cap on Aref (C11)?

Completely gone in #6 isn't it.

@BitSeeker

Don't think that 0.1uF should be connected to xtal?

Was mentioned here already and

@spencerlommel1

@BitSeeker I think you're right!

And seen, resulting in

@spencerlommel1

Removed connection to AREF and left it floating

[jim-p]

Where does RST go?