Using a standalone atmega32u4 instead of Arduino nano to shrink project size


I'm working on a project for quite a while now and its working pretty good but I want it to get on another level. Right now I use a 2 layer pcb with only through hole components and so the size of it is pretty big. Here is a picture of it:

I want it to become way more compact and get rid of all through hole components and use smd ones instead. It would be perfect to get rid of all components underneath the 7 seg displays.
To accomplish this I need to switch from the Nano to a standalone Arduino, at first I thought to copy the nano but the atmega328 needs a second chip in order to ensure usb communication and after a bit of research I came up with the atmega32u4 which has a usb interface built-in.

As I'm not really good in electrical engineering I'm a bit lost at this point. I found a few topics (like this) which seem to adress the same problem but I have issues understanding which parts I really need to get it to work as a standalone and how to arrange them in the schematic (best in fritzing, because I use it for my pcb design aswell).

Could someone of you give me a little starting help on what parts I need and how to arrange them or does someone even have a better idea on how to shrink my project? Maybe another chip or something else?

Some key facts that may be needed:

  • I need the USB connection, because the Arduino communicates over the serial port with my desktop app and the user should be able to update the Arduino sketch via USB
  • I dont really need the ICSP headers if I get an atmega with a preloaded bootloader, maybe I can save space there? (or should I keep these just in case?)

Thanks in advance and happy new year!


You can look at the schematic of a Sparkfun Pro Micro.

I would keep the ICSP (just in case); looking at your board, there is still space at the left and right of the 7-segment display for 6 pins.

You can also look at the schematics for the ItsyBitsy 32u4 or the Teensy 2.0. They’re all pretty similar and pretty minimalistic. If you want to pass compliance testing you’ll need additional components. I think the ICSP is a good idea in case you need to alter the bootloader, but you could use a smaller form factor for it and just solder wires ln in a pinch.

I also had similar requirements and ended up designing my own 32U4 based PCB.

I would definitely advice to keep the ICSP connector in order to burn the bootloader.

I also burn the bootloader before soldering the MPU using a ZIF TQFP44 socket, however there have been occasions that I needed to burn it again.