The device presented here can generate a complementary clock signal at frequencies of 10Hz to 10MHz in steps of factor 10. Thus, I chose to call it 10xHz clock generator (with x being a number between 1 and 7). It can also be used to manually create clock impulses using a press button.
http://www.triplespark.net/elec/oscillator/ClockGen10/
This circuit provides a digital square wave that can be viewed directly or used to drive other circuits. It used the CMOS 4047 Low-Power Monostable/Astable Multivibrator.
http://members.tripod.com/~baec/articles/clock.htm
optosolated circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit, provides 5000V isolation from line
http://www.imagineeringezine.com/PDF-FILES/60hzclk.pdf