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I was hoping someone would be able to have a look at a schematic for a split keyboard I've been working on. I know there are quite a few designs online but most of them are using a processor on a breakout board and I would like to have the chip directly on the PCB. I wanted to be sure I have the bypass capacitors done correctly. Any advice would be appreciated. Thank you

Hi-Res Schematic

******************SOLVED FOR NOW******************

I appreciate the help, thank you. That should give me plenty of homework. I will re-post the schematic when I take care of those issues.

******************CAPACITOR SIZING & PLACEMENT******************

I've been looking through the 32u4 datasheet for clarification and they suggested a 10uF capacitor on the VBUS. I believe having extra capacitors would be fine but wanted to check. So far I was planning on the following:

  • VBUS [PIN 7 ]: 10uF, 1uF
  • VCC [PIN 14]: 10uF(bulk?), 1uF
  • VCC [PIN 34]: 100nF
  • UVCC [PIN 2 ]: 100nF
  • AVCC [PIN 24]: 100nF
  • AVCC [PIN 44]: 100nF
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    \$\begingroup\$ It's not public. \$\endgroup\$
    – Janka
    May 20, 2020 at 16:02
  • \$\begingroup\$ It should be now. \$\endgroup\$
    – K. Solowoniuk
    May 20, 2020 at 16:11

2 Answers 2

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Any advice would be appreciated

  • I don't see any pull down resistors on the rows - maybe they are internal and set-up in your code.
  • I don't see pin numbers on devices - this makes it hard to check things.
  • You don't have notes on the circuit that tells prospective layout guys (if used) how to position the decoupler capacitors.
  • I'd consider putting power reverse protection on the incoming power supply on J1. It looks like it may be a USB connector so I'd also be concerned about adding TVS diodes to protect from ESD event surges.
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  • \$\begingroup\$ It's a ATmega32u4-au from what I understand it has internal resistors, but I will definitely check into it. (sorry for the lack of details. It's my first attempt at electronics) Thank you \$\endgroup\$
    – K. Solowoniuk
    May 20, 2020 at 16:23
  • \$\begingroup\$ When it comes to the decoupler capacitors; for each voltage input there is a corresponding ground pin on the chip. If I understand correctly the capacitors should be connected between these pins (VCC -> GND, UVCC -> GND...) as close to the chip as possible. Is this correct? \$\endgroup\$
    – K. Solowoniuk
    May 20, 2020 at 16:33
  • \$\begingroup\$ You should use a capacitor for each power pin and connect that capacitor to ground via the ground/earth/0 volts plane - they should be sited close to voltage supply pins and not close to grounding pins. As close to the chip as possible, yes. \$\endgroup\$
    – Andy aka
    May 20, 2020 at 16:35
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  • What value is R1/R2?
  • You should be including TVS diodes on the USB lines
  • Are all the caps after the USB connector for decoupling? Which line do they belong to?
  • You should probably include some bulk capacitance
  • I believe you need resistors for the LED's to limit current there
  • Is J1 a USB port? Why is it labeled an ICSP part? Check that you have the right part there. If it is an ICSP, it should not have D+/D-...
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  • \$\begingroup\$ R1/R2 are 22.6ohm (I was trying to clean up the schematic and removed useful information.) \$\endgroup\$
    – K. Solowoniuk
    May 20, 2020 at 16:38
  • \$\begingroup\$ J1 would be where the USB cable connects, I just want to have the cable soldered to the board using pads or thru-holes but wasn't sure what to add for a component. I used the same component on the I2C connection as placeholders until I find the correct component. \$\endgroup\$
    – K. Solowoniuk
    May 20, 2020 at 16:46

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