I am trying to make a delay using a 555 timer. The delay should be 20second off and 1us on!!i tried all the calculation but i couldn't get the output from the multisim oscilloscope!!can some one please help me with this??
thank you!!

 

Try this site, it might help
http://www.kpsec.freeuk.com/555timer.htm#astable

 

Not brillian, or tried, but maybe simple: A 555 one shot can give a positive 20 sec. pulse, but maybe you could differentiate trailing edge with .001 cap & 1k resistor, cleaning up neg spike with an inverting schmitt trigger or a comparator.??

 

How square and accurate does the 1μs pulse need to be?

 

A 20 million to one ratio with resistors and capacitors? I expect to learn something from this one!

 

As I said : .001 & 1k into a 40106 and out came a flat topped 1.2μs + pulse. It was sure a skinney little thing tacked onto end of 21 m + pulse.