What is it?

A Pro Mini with an ATmega 1284p instead of a 328p.

So what, right?

Well, replacing the 328p for a 1284p expands your program memory.

From a measly 32KB to a whopping 128KB!

That's 4x as much!

Did I mention that the board is the same size as the original Pro Mini?

Or that it has a pin-compatible layout?

Effectively making it a drop-in replacement - just see the FAQ below for a few caveats!

Why did you make it?

You can read more about the journey over on my Hackaday project page, but in a nutshell...

As my Pro Mini based projects inevitably succumbed to feature creep, I began to push the limits of the 328p's 32KB of program memory.

Since, in many cases, I already had a project board into which the Pro Mini nicely plugged and/or a project box into which everything comfortably fit (or was stuffed!), I didn't want to have to redo it all just to try to fit one of the other 1284p or 2560 development boards.

But I still needed more program memory.

What was I going to do…?!

[Queue dramatic dilemma music!]

In the end, I taught myself SMD circuit design, layout and soldering, and…

BEHOLD!

The Pro Mini XL was born.

What makes it special?

Did I mention it has 4x the program memory of the 328p based Pro Mini you already have and are currently being confined and constrained by?!

So that's 128KB to play with instead of only 32KB - just in case you weren't paying attention.

Other notable special-ness over and above the original Pro Mini includes:

• 8x the SRAM (16KB vs. 2KB)
• 4x the EEPROM (4KB vs. 1KB)
• One extra UART
• One extra External Interrupt (v2 Only!)
• One extra 16-bit Timer
• JTAG interface

Really, what more could you ask for?!

Frequently Asked Questions (FAQs)

No Regulator

Yes. There is no built-in regulator on-board.

But the good news is that the chip itself accepts 1.8v to 5.5v on the VCC pin depending on the speed you’re clocking it at.

Wait, what? No regulator?!

Come on man!

Look at the size of that ATMega chip compared to the rest of the Pro Mini board!

I mean, something's gotta give, right?

And be honest, how often are you powering your projects from a Pro Mini regulator, seriously?!

But if you really want a regulator, let me know (which one?) and I'll try to fit it in there...just for you.

And you'll note that with the new v2 board layout, I've cleared just enough room (I think) above the reset switch for a small regulator and it's associated components.

So, what would you like?

3.3v/5v Selectable LDO?

Boost Converter?

Please, let me know!

Unrouted Pins

Try as I might, my place-and-route fengshui was insufficient to get chip pins 23 and 26 to 31 of the 1284p TQFP routed out of the rats nest of tracks and vias underneath it.

These are mostly just ADC inputs (pin 26 to 31) and TOSC2 (pin 23).

I am working on it though and currently have a layout revision that gets 3 or 4 more pins routed out.

Let me know if you want more pins (and which ones) and I'll try to take another shot at it.

Development Board Alert!

This is my third time designing a board like this and as such it is still very much a work-in-progress.

So I’d really appreciate any constructive feedback or advice to help improve it and/or make it more useful.

But it does work!

And will arrive to you with all the pins tested by me and ready-to-roll with an Optiboot bootloader and Blink sketch already loaded to show off that fabulous LED.

What's all this v2 business?

I had a few comments from customers of the original (v1) board saying that they didn't need so many ADC inputs and instead wanted the extra interrupt, the two analog comparator inputs and the timer/counter inputs.

So I wrestled with the layout for a while and produced this v2 board.

Other customers actually preferred having more ADC inputs and so I'm continuing to make the original (v1) board available in my Tindie Store:

Pro Mini XL - v1 - ATmega 1284p (With More ADC Inputs)