-
http://www.atmicroprog.com
-
http://www.pmillett.com/tecnical_books_online.htm
-
http://elm-chan.org/works/akilcd/report_e.html
-
http://www.flickr.com/photos/guero/100626389/in/set-72057594065563994
-
http://mcnally.cc/amps.htm
-
http://wiredworld.tripod.com/tronics/audio_level.html
-
http://www.sample.co.kr/clock/index.html
-
http://www.jogis-roehrenbude.de/Roehren-Geschichtliches/Nixie/IV-4.htm