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This describes the mods for the 2018 version (this particular board only) recognisable by the 'servo' headers on 3 edges. Here's where I bought mine:
https://www.ebay.co.uk/itm/Pro-Mini-ATm ... 2484056646
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There are a few nice additions to this version, for example it has a 16mhz crystal rather than a resonator, so it will be more accurate and more stable than the previous versions which used ceramic resonators. It has a nice 'power input' header, for which an optional connector shell is supplied. The servo headers are the 'sensible' way around (ground round the outside edges, signals on the inside) and it also has an icsp header (see below). Note that the ebay seller has the header pin colours wrong AGAIN! They should be black on the outside, red in the middle and yellow on the inside. The "neg/pos/signal" screen-print on the PCB is correct, G=ground, V=5v, S=signal. DONT copy the pictures!
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Click to enlarge:
The aim of these mods is to provide a simple 3-pin header for our RF module, carrying neg, battery and PPM, which in the sketch will need to be placed on D0 (also known as RXD). I've traced the layout and found that the 5v input (which we dont need) can easily be isolated by removing the series schottky diode. Here's the board as supplied, note the schottky position above the 5v regulator:
Here are the traces, in red, showing the 5v input going to the diode, and 12v input to a capacitor:
So first we remove the diode - its much easier to do this before adding the headers!
Having isolated the 5v input header, we can now use it to provide battery voltage to the RF module.
This is done with a short diagonal strap from the upper diode pad to the lower end of the SMT capacitor:
Heres a closer look:
Now we have battery voltage on what was the 5v input pin, we can add the RF module header - neg, battery and PPM (RX/D0):
Here's a video showing the modification, its very easy but dont overheat the SMD capacitor:
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Programming is via a proper ICSP header, you can either solder in the header pins, or do as I did and just temporarily plug in the usbasp whilst programming:
I've tested this before posting and until they inevitably change the boards again, this is gen.
With the mods suggested the new 2018 board is ideal for propo and reeds encoder projects.
Finally I can confirm that they have fixed the A4 & A5 transposition, those are now straight,
however, they have transposed D0 and D1 on the silkscreen annotation.
Counting along the header towards the reset button it actually goes D1, D0, D2, D3, D4, D5, D6, D7
The mod of course uses D0 for PPM (so the second pin along on this row is left unconnected),
This is because Rx is D0, they're the same pin, so we use Rx on the 'new' module header.
Cheers
Phil
Good to see that the boards are continuing to improve for our purposes/applications, and that there is now a proper ICSP header, all in a smaller form-factor.
Bugger! 
. However, I'm sure the budget can stretch for several of these, for "research purposes" of course! 
I found if you look and pick up the dingy dirty ones for $20 or less, they usually clean up pretty nice. Quite often the boards are overcome with corrosion but the boxes and gimbals are usually in good shape after some work. I'm going to start a 'square box' trend with a S/C button on them