how to generate pulse 1 second with 555

Thread Starter


Joined May 17, 2008
i want to make a digital clock....
how to generate 1 second pulse with 555 ??
how to calculate the time constant ( R &C) which help 555 to generate pulse? please reply


Joined Apr 27, 2007
I have my reserves when using a 555 as a timing generator for a clock. With a 555 you can't generate a enough precise signal, even if you use low tolerance resistors and capacitors (below 1%) for your time base.


Joined Apr 26, 2005
How precise do you need to be?

Solutions include:

Divide your line frequency.
Divide a crystal frequency.
Buy a GPS receiver with 1 PPS out.
Buy a Cesium Oscillator.


Joined Jul 17, 2007
cumesoftware is absolutely right. You will be very unhappy with the accuracy of your clock if you try to use a 555 timer.

There are a couple of 4000 series CMOS ICs that will help you out, depending on what you want to do; run from the power company's 60Hz signal, or do your own crystal-controlled clock.
The 4040 can be used to get a 1Hz signal from the power company's 60Hz AC.
The 4060 can be used to generate a 1Hz clock using a crystal. This is what you need for a battery-powered clock, or if you want a backup clock for a line-powered clock.

You can get datasheets from ON Semiconductor's site; these applications are shown in the datasheets:
Part numbers: