This is my DIY clone of the ControLeo Arduino Leonardo PID controller minus the transistor to allow the Arduino to control the backlight (I leave mine on all the time) and minus the "+5V Auto Selector" which I don't think I need (see schematic for details).
Note: Does anyone know why "+5V Auto Selector" is necessary? I just bind VUSB into my +5V bus and it seems to work just fine without this selection logic. When the USB is providing power, the 3.3V regulator works fine and though there is "back pressure" on the 5V regulator, but it doesn't seem to be a problem. When the power jack is powering the unit, everything is fine. And when both power supplies are present, everything seems to be fine then too.
I went with a Pro Micro (Chinese clone of - 2 for $12 including shipping. Note the bottom corner of the board where they even rip off the Sparkfun logo, and print Sparkfun on the back as well) because it was cheaper than a QTY 1 ATMega32U8 chip from Digikey, not even considering a dollar or two for the adapter. The discretes and the two regulators are close through-hole alternatives for the SMT discretes in the schematic and the rest of the ICs are the exact ICs called for, of course.http://www.kickstarter.com/projects/1471240030/controleo-an-arduino-compatible-controllerhttps://raw.github.com/engineertype/ControLeo/master/ControLeo-Schematic.pnghttps://raw.github.com/engineertype/ControLeo