Should I use original board dimensions?

If I make my own arduino compatible board, should I use the dimensions as well as the pin placement as the original board or I can use whatever I want?
Personally, if you consider buying a clone or a compatible board, would you buy what is not looking the same as the original? I want a board that have more functions but it may produce a bigger board than the arduino one.
Also, can I just make my own design with own chose of the components legally?
So for example I make an arduino leonardo based board which is bigger than a leonardo because of some kind of component.

Yes you can. The Arduino is open source, you can make it identical or very different. The only thing you can’t do is call it an Arduino.

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You are in control of your own projects.


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If you are making this to sell then your board needs to be certified for the places you want to sell it in. That will be CE if in Europe or FCC in the U.S. other places like Canada, Australia and China also have their own regulatory bodies.

These mainly involve emissions testing but there is other stuff you have to satisfy.

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I'm asking the dimensions because I have seen some boards that can be plugged into the arduino board but if I change the sizes and the placement, it won't be compatible with those boards, and also with that plastic holder thing which comes with the original board

Yes that is your decision to make. Every decision has positives and negatives consequences.

If you make the board bigger to accommodate more options, you can still use the original pin spacing and put the extra stuff outside this footprint. And so have the best of bothe worlds.

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For instance, we designed the NKC "Freeduino" board to be slightly larger than the official Arduino (pushed the board to the left and had the connectors there hang less off the board, got rid of the "Italian Styling" on the right.) But it maintains the spacing of the important connectors, so it still works with most shields.

OTOH, other companies have built whole ecosystems around other board shapes. Like the Adafruit "Feather" and "Itsy Bitsy" boards, the "Lilypad" boards for wearable computing, and a slew of boards designed to use with 3d printers than have an Arduino-programmable core, plus room for a bunch of motor drivers and such.

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If you plan on plugging into an Arduino you must keep the connecters in the same location and have similar function. The board however can be bigger.

Consider if you want to plug it into one of the solderless boards for testing when you place the connections.

I recommend what ever you do, keep the connectors and pins on a 2.54mm grid. And when I make a board I:

  1. Never make a connection under an IC (if possible) If you find out you need to cut it for some reason you won't be able to.
  2. I bring all µP pins out, even if it is a short trace I could later scrape the solder mask off and solder a wire.
  3. If you don't have a space problem you should add capacitors on the analog inputs, and maybe a resistor divider. You can always leave parts out.
  4. An on board LED is good for testing.

That's all I can think of for now.

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Thanks for the answers! Appreciated!

"I recommend what ever you do, keep the connectors and pins on a 2.54mm grid."

Yes, I want to keep that, but what about the original spacing problem on the leonardo between pin 7 and pin 8? Should I keep that?

That goes all the way back to the original Arduino, not just the Leonardo.
It was originally a mistake but was kept to be compatible with the few shields made for the first batch. All Arduinos with this board size have this half gap.


The suggestion of 2.54mm grid is so the numerous connectors out there will fit your connections. The only reason to keep the P7 - P8 distance is if you plan on using existing shields.

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But of course, if you do not desire/ require compatibility with existing "shields", then nothing about the conventional header arrangement and pin allocation matters anyway, does it? :face_with_raised_eyebrow:

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While that is true, keeping the 2.54 mm spacing for the connectors is good design unless one wants to move to a whole different connector system.

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Some other thoughts:

  1. I often use the 2 or 3 screw terminal headers for power in.
  2. Micro USB connectors are terribly fragile. If you decide you need one try to get one with through tabs or at lease a lot of board area for the shield solder connections.
  3. I am liberal with the number of ground pins / terminals etc.
  4. Mounting holes. I try to get at least 3.

When I say 2.54mm connector spacing I'm talking about these (either SMD or through hole)


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Well, 1/10" = 2.54 mm is one standard. There are others and have been many. It is much a matter of what is readily available and reasonably compatible.

I certainly was not suggesting any other connector type, but saying the placement is somewhat arbitrary.

In which case there is an argument for using them for "power out" as well. :grin:

You can end up with a "screwshield" form.

Depends on just what you are designing.

The UNO form is intended to be used with a shield. It is not appropriate on its own for connecting more than one or two attachments. The Nano/ Pro Mini can work with a breadboard. If you need to actually construct a usable device, you either make a shield for the UNO, or mount your Nano on stripboard or a custom PCB. Or perhaps you use a Nano with an "expansion shield" which multiplies the ground and supply conenctions.

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Wow, thanks for these informations, appreciated!