The Microcontroller Hobby blog has posted a handy new tutorial by Eric Wolf explaining how to control high current devices from a microcontroller. Eric explains how to use what he describes as "the cockroach of transistors", the NPN BPJ 2N3904 to drive up to a 170ma load. Robot builders may question the idea that a 170ma load should be described as "high current" but reader comments at the end of the article point out that a MOSFET could be used to controller devices in the 30A-50A range.