I will do battery powered ultrasonic parking sensor

I found a lot of similar parking aid projects, but they all, for the most part, call for tying up a full sized Arduino and providing DC power through a wall wart. I wanted something stand alone that could run for months off AA batteries. A low-cost embeddable board like the Pro Mini might have worked, but most use LDOs and have power LEDs, so waste power.

This is a useful example project, I think, to intermediate Arduino users who want to put their project onto a PCB. The routing is much simpler than a full Arduino-compatible board because no unused pins have been brought out to headers. It provides ICSP and serial headers for programming and debugging. You could easily take this layout, delete the parking related stuff, and route in your own project components. It uses an LTC3525 boost chip to provide 5V or 3.3V from one or two AA batteries.