with ADC0820 connected to the printer parallel port
http://www.geocities.com/lptscope/
By Finn Haugen, Telemark College and TechTeach.
http://www.techteach.no/publications/control_toolbox_matlab/cst4.htm
Switch you TV lamp while comfortably seated on you armchair, using your TV remote control
http://www.nutchip.com/progetti/tv_light_en.htm
http://koumes.misto.cz/_MAIL_/navody/tvmodulator/tv.html
http://home.att.net/~theremin1/Circuit_Library/twin_t_oscillator.html
http://www.mrs.bt.co.uk/dubus/8604-4.pdf
in a three-phase system
http://www.edn.com/archives/1995/090195/18di1.htm
http://ourworld.compuserve.com/homepages/Bill_Bowden/page5.htm#flash2.gif
The first transistor acts as a reflex stage. A 10 millihenry choke sends the RF to the diode detector and the audio to the output stage.
http://www.techlib.com/electronics/crystal.html#Twotransistorreflex
Discusses the various ways that a voltage regulator can be made using two transistors.
http://www.4qdtec.com/theory/2TrRegs.html