I have learned about many circuits which use a timed clock pulse. How is the clock pulse generated?

That depends whether original circuit is DC or AC. In DC there could be used e.g. Multivibrator

https://en.wikipedia.org/wiki/Multivibrator

If it's AC there can be used e.g. transformed to increase/decrease number of cycles from original 50 Hz/60 Hz.

You can use e.g. Zener diode for clipping sinus wave like here:

 

 

 

Edited August 11, 20187 yr by Sensei

For a lot of equipment- where the clock rate is of the order of KHz  or MHz and Ghz they use crystal oscillators.

https://en.wikipedia.org/wiki/Crystal_oscillator

 

 

 

Are 555 timer chips still used?   555 timer IC - Wikipedia:  https://en.wikipedia.org/wiki/555_timer_IC

 

 

41 minutes ago, Frank said:

Are 555 timer chips still used?   555 timer IC - Wikipedia:  https://en.wikipedia.org/wiki/555_timer_IC

 

Probably only by old  crocs like me.
:-)

14 hours ago, John Cuthber said:

Probably only by old  crocs like me.

...or not... "As of 2003, it was estimated that 1 billion units were manufactured every year. (...) The 555 is the most popular integrated circuit ever manufactured"..

I have few as well. Using/reusing them on breadboards.

 

On 8/11/2018 at 9:55 PM, John Cuthber said:

For a lot of equipment- where the clock rate is of the order of KHz  or MHz and Ghz they use crystal oscillators.

https://en.wikipedia.org/wiki/Crystal_oscillator

That's right. Most watches used to have "quartz" written on the face as reference to the quartz crystal used. Now a lot of clocks are kept accurate by radio signal, but I think this just provides a periodic correction, and the oscillators are still crystal based.

14 minutes ago, mistermack said:

That's right. Most watches used to have "quartz" written on the face as reference to the quartz crystal used. Now a lot of clocks are kept accurate by radio signal, but I think this just provides a periodic correction, and the oscillators are still crystal based.

Right - a stand-alone system needs its own oscillator (because you won't always have access to the signal), and would do periodic synchronizations

A lot of plug-in clocks use the mains frequency as their oscillator

Yeah I have seen 555-timers etc used before I was just was wondering at the processes they use to ensure that a pulse only fires every minute for example.

3 hours ago, fiveworlds said:

Yeah I have seen 555-timers etc used before I was just was wondering at the processes they use to ensure that a pulse only fires every minute for example.

One option is to use a 555 and a divider but dedicated chips for that sort of role are available.

Her's an example which shows how old fashioned I am
http://www.ti.com/lit/ds/symlink/cd4060b.pdf