Built a 1284(p) into a 328p Pro Mini footprint. Not sure what to call it, a Pro Mini XL maybe?
I now have x4 the program memory (128K vs. 32K), x4 the EEPROM (4K vs. 1K) and x8 the SRAM (16K vs. 2K) all in a 328p Pro Mini pin-compatible (I think!) footprint of about same size.
I can also run at 20MHz vs. the usual 8MHz provided I’m prepared to run it at 4.5v and above.
Had to sacrifice a few pins and components, but might be able to put various selections back in future revisions. Nothing major (in my opinion) just components associated with the regulator really. I also went for a crystal (not installed yet, on order, LEDs too..) over a resonator - just a personal preference for when timing is critical.
And yes, those are 0402 SMDs. I actually did them by hand (!) with a microscope and a judicious amount of coffee; a fine-point iron, solder wick and flux became my best friends.
So far, I’ve had it working with nRF24s and RFM69s radios, ATSHA for personalization and external flash for FOTA. The DualOptiboot bootloader code and makefile needed a bit of tweaking, but nothing major.
I broke out the JTAG I/F but haven’t played with that yet and also added power pins next to the I2C to make some of the sensor modules (like SI7021) pluggable - see below.
I also want to play with the QTouch library support for built-in capacitive touch buttons, sliders, etc.
Why not just go with an ARM (STM32, SAMD, nRF52)?
I’m working on it! ;o)
Am not wanting to start a(nother) 8-bit vs. 32-bit discussion. I’ve got an AliExpress package of 32-bit MCUs coming (very) slowly to me. When it arrives, I’ll start experimenting and exploring - probably with the nRF52s, since those seem to be the flavor-of-the-month and very capable-looking chips...
But until then, I need more program memory!
(Among other things…)