how to get exact 1 second square pulse without tuning is any ic available in 555 we have to tune i need without tuning resistance. if using 555 how to calibrate it to exact one second pulse in cro it is difficult to se one second square pulse pls help
I think you can try with any wall clock circuit. They have a small microcontroller programmed to produce exactly 1 sec pulse. They are quite cheap and easily available.
It should be noted that the accuracy of the pulse of the clock circuit (or any digital circuit producing this pulse) is dependent upon the accuracy of the crystal generating the clock frequency. So how "exact" a 1-second pulse do you need?