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@Gordon
Hi,
To connect NFC you just need to add an NFC antenna to the pins D9/D10 labelled with 'NFC' here: http://www.espruino.com/MDBT42Q#pinout
Now getting NFC tuned perfectly is more or less magic - there are so many different things that affect it (including measuring probes!) that you basically need to put the aerial on, see where it resonates (using a grid dip meter or similar) and try different capacitance values. It's why I don't put capacitors on there.
The good news is that actually unless you're going for super high range, none of that actually matters. I've had a lot of success just wrapping a bit of wire around a 4cm diameter circle 8 times, and then connecting it to those 2 pins with no capacitors at all - in fact that's what I use for checking NFC on the MDBT42Q breakout.
I'd definitely give that a go first, before buying a specialist antenna.
If you really wanted to try capacitors then I'd suggest using 2x 100pF capacitors, but from my experience the actual value you need to get it perfect could be anywhere from 50-200. If you bought an antenna you'd hope that the antenna manufacturer would give you a rough idea on the capacitor value to use though.