William Butterton didn't set out chasing some flashy idea of easy money. In fact, he was skeptical of the whole concept of passive income. But after his first child was born, the full-time electrical engineer told Business Insider he started looking for ways to bring in extra income without sacrificing time with his family. That search eventually led him to something surprisingly simple: placing ATMs in local businesses. Today, Butterton and a business partner run a small operation with five ATMs and thre ...