Scots Guide to Electronics
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Analog Techniques…and Audio
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/Analog.html
Information and Measurement
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/iandm/intro.html
University of St Andrews_School of Physics & Astronomy