Didn't Get Sent an Arduino UNO Mini LE? Make Your Own Feather M0-Inspired Variant!

If you were very lucky. you might have found a parcel in your mail stop a few months ago, sent from Arduino themselves...

On opening it up, lucky recipients would find a special little board — an Arduino UNO, but almost ant-sized!

This dinky little development board is a testament to the progress of technology — showing what 10 years can do to the size of the silicon that sits on this board.

Featuring the same two chips — an ATmega328p at heart, and an ATmega16U2 to handle the USB communications, the UNO Mini LE is simply a scaled down sibling of its former self.

Marking a bit more than a decade since the launch of Arduino, and additionally, celebrating the sale of the 10 millionth(!) Arduino UNO board, the UNO Mini LE is more of a collectors item than a practical prototyping board, what with the half-pitch, 1.27mm headers quite obviously breaking any compatibility with previous shields...

Packaged up in a pretty little presentation box, you'll be keeping an eye peeled for these to pop up in the background of videos from some of the more prolific content creators in our circles.

No Mini today — the stock has gone away.

That LE doesn't stand for Low Energy though... Nor does it hint at any Bluetooth LE capability, boo. No, the LE stands for Limited Edition, which loosely translated, means "you can't' have one." Sorry.

Well. It's a good thing that this is a community of makers, right?

@tinyledmatrix is a dab hand when it comes to recreating difficult to source designs.

We know them for their diminutive DIL-format LED matrices, a range of refixes of the these-days rare-as-rocking-horse-poop digital display indicators of yesteryear!

With a plan in mind to reimagine the recent UNO Mini LE, with a parts list that doesn't require ridiculous MOQ, @tinyledmatrix has really delivered on his derivative of... the derivative... of the UNO. It's t̶u̶r̶t̶l̶e̶s̶ derivatives all the way down...

KiCAD keeps on getting more capable!

Starting with the sources for the UNO Mini LE, many of us would have been stuck only some years ago.

Why so? Well, because the Arduino team use Altium as their EDA package. It's fair enough, they can no doubt afford it, and the enhanced functionality that it offers — perfect for projects such as the packed-out Portena PCB.

Most of us are more comfortable with EAGLE, or more recently, KiCAD as our EDA toolset.

While EAGLE has been seen less and less since Autodesk started driving people away, KiCAD has been gaining users, and functionality, at a pretty impressive rate.

Recent builds boast the ability to import data from Altium files directly, something which opens up a world of potential inspiration, allowing the importation of previously incompatible source files.

Mixing in a bit of the ol' Metro M0...

Thing is, the Mini LE is a true homage to the original UNO, in that is uses two separate — and fair to say, old — chips to do what we can nowadays do with just one. And do it much more capably, we might also add.

While the ATmega chips have a long standing legacy, and won't be looking at EOL for quite some time yet, it's fair to say that the last decade has been pretty good to us.

We now have access to vastly more powerful chips that can easily provide all of the functionality - and far much more — as the iconic duo found in the original UNO design.

Originally released as Atmel parts, now branded as Microchip, the SAM D21 range of 32-bit Arm Cortex-M0 MCU made their way onto many maker boards, notably including the Adafruit Metro family.

Comparing the two schematics, we can see that the single chip solution is definitely more succinct.

With a much more powerful MCU that can also handle its own native USB communication, it makes a good deal of sense to see @tinyledmatrix mixing the old up with a bit of the new!

Upgrade that UNO!

Taking the best of both worlds — the form factor of the UNO Mini LE, and the beefy brains of the Metro M0 boards results in a refix that actually makes a lot of sense.

Fusing both together results in the feature-packed, femto-sized fabrication we see below — the miniMetroM0! All the brains of the modern Metro boards, in a dinky development board form factor!

While making provision for more modern parts, @tinyledmatrix also took the time to throw in a few extra titbits on top of the original UNO Mini LE design. Most notable are;

• A Qwiic / Stemma QT-compatible (JST 4-pos 1.25mm) I2C expansion header
• A chunk of external SPI Flash (a handy tip from the Metro design)
• A physical, ON/OFF SPST power switch(!)
• A WS2812-compatible sk6805 EC15 Digital RGB LED. (1.5mm²!)
• The TAG-Connect programming header that is often found on smaller,

Tag Connect is a bit of a love-it-or-hate-it solution. It's great for it's intended application — space-constrained boards, where there simply isn't room enough for the standard programming headers, but a pain if you are without the requisite pogo-pin adaptor.

There are a few open source alternatives in development however, including @tinyledmatrix's own homebrew, seen above, along with this neat OSHConnect variant from @timonsku.

Shockingly smol shields!

I mentioned earlier that the UNO Mini LE formfactor isn't exactly compatible with your slew of R3 form-factor shields...

Well, beyond bespoke boards such as this Mini LE variant, @tinyledmatrix is well versed in designing... yup, tiny LED matrices!

As if this miniMetroM0 wasn't cool enough, @tinyledmatrix has gone the extra mile here, showing off a smattering of super small RGB LEDs, 141 to be precise, in a stunning, stacking shield, compatible with the footprint of the UNO Mini LE!

Feel like making your own miniMetroM0?

This is a super-small special edition that anyone can get their hands on! Now that @tinyledmatrix has gotten the bootloader blinking, the rest of the pin testing shouldn't take long at all!

While the GitHub repo for this project is currently little more than boilerplate, we're sure we'll be seeing some source files soon enough.

There's a HaD page for a bit more insight on this dinky little development board, but for the enthusiasts, we'd suggest giving @tinyledmatrix a follow on the ol' bird site — @tinyledmatrix.