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enif
I entirely agree with dc42 that the Arduino Pro Mini is not the best choice, but it actually does have the 5V regulator onboard. So that it's possible to run it from 12V - it's the pin labeled "RAW". Here a link to the schematics for those interested.
Thanks for the correction. I didn't spot a 5V regulator in the picture of the pro Mini, but on closer inspection I see there is an SOT23-5 chip so I guess that's it.