Ladyada's guide (http://www.ladyada.net/learn/arduino/ http://www.ladyada.net/learn/arduino/) has all of the basics to get you started with the physical parts o

Ladyada's guide (http://www.ladyada.net/learn/arduino/ http://www.ladyada.net/learn/arduino/) has all of the basics to get you started with the physical parts of hooking up your Arduino. I've glanced at "Lessons in Electric Circuits" (http://www.ibiblio.org/kuphaldt/electricCircuits/ http://www.ibiblio.org/kuphaldt/electricCircuits/) by Tony Kuphaldt, and it seems to cover all of the physics that you would need to get started with hardware hacking. Volume I appears to be the most relevant to you, covering the basics of voltage and currents. Once you understand that, you'll most likely be looking at specific parts that perform all of the complicated electronic functions (A/D Converters, H-Bridges, Omp Amps, etc), and don't need to fully understand the physics behind them, although it helps. I'm currently going through "Making Things Talk" by Tom Igoe, whose audience appears to be non-technical, or at least non-hardware, people. It does not cover the physics and math behind the projects though.