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.