A part for a DC 5V TO ± 12V Mini DC converter module available from Ebay (and probably others). Search for “DC 5V TO ± 12V Mini DC converter” and you will likely come up with them. Takes from 2.5V to 5.5V in and produces +/-12V at around 30ma enough to run op amps, da/ad converters, or rs232 drivers from either the power bus (5v or 3.3V) on your micro or a 3V battery. The part has all three views, breadboard, schematic and pcb but hasn’t been actually cut as a pcb at this point.
DC 5V TO ± 12V Mini DC converter.fzpz (7.4 KB)
edit: to help with selection here is a screen shot of the bb view. It should provide a sense of the size of the module and help in selecting the correct one on ebay: