In the study of electronics, the concept of duty-cycle pops up in various places such as digital circuits, one-shots, switching regulators, and DA converters to mention a few. Lab experiments to examine duty-cycle usually require two parts- a square-wave oscillator driving a monostable multivibrator (one shot).
http://www.elexp.com/t_oscill.htm
handful of components configures a current-feedback op amp as a large-amplitude sine-wave oscillator with independent adjustment of amplitude and frequency
http://www.edn.com/archives/1995/060895/12di5.htm
this circuit draws a mere 500nA from a 6v battery. It uses a very inexpensive C-MOS IC to produce a frequency of 2Hz. However, by changing the component values you can push it to 300Hz.
http://www.imagineeringezine.com/PDF-FILES/500na0.pdf
works much like the classic 555 timer, but draws only about 1.5 microamps from a 3 volt battery, highly stable under varying temperature and supply voltages
http://www.imagineeringezine.com/PDF-FILES/10secosc.pdf
This Design Idea describes an oscillator in which setting the resistance of two digital potentiometers independently programs the oscillation amplitude and frequency. This design idea uses diode-stabilized Wien-bridge oscillator that generates accurate si
http://www.edn.com/article/CA198897.html