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At exactly what signal point in the circuit do you need this duty-cycle?
One way to do that is to use the 1 sec pulse to trigger a one-shot (such as using a 555) with the desired pulse-width.actually I need either 99.97% or 0.03% duty cycle in 1sec clock pulse. I don't have to vary. I should have been tell it before. sorry for the mistake. this clock pulse I'll give to CD4026 to enable and disable the clock.....
One way to do that is to use the 1 sec pulse to trigger a one-shot (such as using a 555) with the desired pulse-width.
You missed Zapper's point: You use the output of the divider chain (1sec square wave) to trigger a one-shot (any will do) You set the RC time-constant in the one-shot to be ~3ms, ero it puts out a 3ms pulse once per every 1000ms, where the one second period is locked to the crystal.but 555 is not very good about to give 1 sec pulse. depend upon the resistor and capacitor which are also temperature depended. I need exact 1 sec pulse all the time with that duty cycle!!!! I have to think with crystal! what do you say????
but 555 is not very good about to give 1 sec pulse. depend upon the resistor and capacitor which are also temperature depended. I need exact 1 sec pulse all the time with that duty cycle!!!! I have to think with crystal! what do you say????
He wants to create the 3% duty cycle at the 1Hz output of his divider chain, not at the crystal.
You missed Zapper's point: You use the output of the divider chain (1sec square wave) to trigger a one-shot (any will do) You set the RC time-constant in the one-shot to be ~3ms, ero it puts out a 3ms pulse once per every 1000ms, where the one second period is locked to the crystal.
Or build a one-shot out of a cmos schmitt-trigger inverter:
oki'll try your circuit. if you don't mind can you please explain what does the diode 1N914 is doing here.You missed Zapper's point: You use the output of the divider chain (1sec square wave) to trigger a one-shot (any will do) You set the RC time-constant in the one-shot to be ~3ms, ero it puts out a 3ms pulse once per every 1000ms, where the one second period is locked to the crystal.
Or build a one-shot out of a cmos schmitt-trigger inverter:
He wants to create the 3% duty cycle at the 1Hz output of his divider chain, not at the crystal.
The 555 can be used with a crystal just like the CMOS inverter you are using now.
View attachment 68778
That does not change the fact that to get the variable duty cycle that you want, it would be better to go with what has been suggested instead of trying to pull the crystal there (even if that range is even possible).
John