What is the smallest microcontroller + SemTech SX1231H combo to date?

[WhiteHare]

Assume it's externally powered, so it could, in principle, be even smaller than the coincell versions that some here have developed.  I'd like to wirelessly monitor battery voltage levels in some pre-built devices, and so for cramming it in whatever crannies there might be, the smaller the better.  Because it's special purpose, I don't need all the pins exposed either (beyond what's needed for the initial setup--after that, it might be encased in epoxy and programmed only wirelessly).

Edit: I originally titled this post "What is the smallest atmega328p + RFM69 combo to date?", but since that got no replies, I decided to expand the question to include the possibility of other very small combo's in the question.

[WhiteHare]

Possibly answering my own question, it looks as though the FreeScale MKW01Z128, which combines a ARM Cortex M0 with the Semtech radio into one compact package, is just 8mm x 8mm (see Figure 8 mechanical drawing on page 28 of http://cache.freescale.com/files/microcontrollers/doc/data_sheet/MKW01Z128.pdf?pspll=1).

As I don't know how much support circuitry would be needed to make it function standalone, for now I'll take 8mmx8mm as a lower bound on the minimum size.  From that perspective, a standalone coincell sized "Moteino", such as Tom's or Joe's, actually comes pretty close in size!

[Felix]

As I don't know how much support circuitry would be needed to make it function standalone, for now I'll take 8mmx8mm as a lower bound on the minimum size.  From that perspective, a standalone coincell sized "Moteino", such as Tom's or Joe's, actually comes pretty close in size!

I can tell you it's quite a bunch.

[TomWS]

As I don't know how much support circuitry would be needed to make it function standalone, for now I'll take 8mmx8mm as a lower bound on the minimum size.  From that perspective, a standalone coincell sized "Moteino", such as Tom's or Joe's, actually comes pretty close in size!

I can tell you it's quite a bunch.

Looking at the RFM69 module, the PA/Antenna matching components take up half the board area so ISTM that a complete solution with this device could be done in a 16x16 footprint (similar to the RFM69CW).  However, pin outs then become an issue...  If you went the RFduino route, with their massively anemic I/O set, then no problem.  If you want to bring out 32 pins of I/O, now you have to get clever with BIG tooling!

Tom

[WhiteHare]

Femtaduino managed to cram an ARM Cortex M0 onto a dime sized board.  A dime is 17.9mm in diameter, so pretty close to Tom's estimate.

I'm guessing something similar could be done with the atmega328p-MU, but I haven't yet seen one.