http://www.ecelab.com/circuit-ultrasonic-t.htm
http://electroschematics.com/wp-content/uploads/2008/04/dog-repellents-schematic.gif
http://code.google.com/p/sixthsense/wiki/Tutorial
http://www.falstad.com/
http://electroschematics.com/wp-content/uploads/2008/04/dog-repellents-schematic.gif
http://code.google.com/p/sixthsense/wiki/Tutorial
http://www.falstad.com/