Ohm's Law and Kirchhoff's Laws with equations, description and examples
http://www.twysted-pair.com/ohms.htm
Digital Electronics, Boolean Algebra, Transistor Level Schematics, and Stick Diagrams
http://www.geocities.com/cmoslayoutdesign/
explained
http://www.microconsultants.com/tips/pwrfact/pfarticl.htm
All inductive devices, operating in d.c. circuitry, which are switched on and off should have a diode connected across their coils to catch the inductive fly back. This page explains why.
http://www.4qdtec.com/catch.html
http://www.musicfromouterspace.com/analogsynth/troubleshoot.html
Construction Idea.
http://www.techlib.com/electronics/construction.html
http://web.wt.net/~geotek/nars/boxes/boxes.htm
Covers theory, materials, tips on winding inductors and eleltromagnets hints and kinks.
http://www.ee.surrey.ac.uk/Workshop/advice/coils/mu/index.html