http://www.web-ee.com/Schematics/Digital_Sine/DigitalSine.htm
60 seconds only.
http://www.qsl.net/vu2upx/Projects/APR9600.htm
http://www.geocities.com/TimesSquare/1965/se_sv811.html
Trying to find a single IC noise source can be frustrating. You could use a single-chip microcontroller, such as Microchip 12C508 for this application. This article gives you idea and software how to do that.
http://www.edn.com/article/CA200385.html
a very inexpensive C-MOS IC that is connected to a small photodiode provides high sensitivity under high ambient light conditions
http://www.imagineeringezine.com/PDF-FILES/4069rvr.pdf
EDN-Design Ideas.
http://www.edn.com/archives/1994/070794/14di4.htm
http://www.mip.berkeley.edu/images/physics/E+10+0.gif
theory, circuits, tips and projects, EEPROM programmer and LCD interfacing
http://users.swing.be/gonzague.colpaert/
A calendar of events of upcoming aurora, meteor showers, eclipses, planets, and more.
http://www.ufowisconsin.com/skywatch/
A circuit that limits the rate of change of a signal; a feature of this design is that the positive and negative rates can be different.
http://freespace.virgin.net/ljmayes.mal/pubs/slew.htm