555 Timer IC – How to Produce a 1Hz Clock Output


I've been messing up with timer ICs, looked up on how they work and now I want to design a simple digital clock using a 1Hz pulse generator. Is a 555 timer IC sufficient enough to make accurate 1Hz pulses or is there any other way to design a pulse gen? Is there a specific resistance/capacitance value for the IC or am I wrong and there's a better oscillator for such purpose?

Best Answer

It certainly would be possible to make a 1Hz signal with a 555. There are (at least) two problems though. a) Assuming that you could get the right cap values and a stable potentiometer, it would be very hard to measure an accurate 1Hz signal with a scope or a counter, since the signal is so slow, and b) The 555 would not generate a square signal. And of course, a RC timer will not be very stable.

If you still want to investigate using a 555, you can square up the wave with a JK flipflop, which will half your frequency in the process. I would also create a much higher frequency, such as 1.024KHz, then cut it with a counter/divider down to 1Hz. That way, you can use your scope to read and adjust your pot so that the 555 is as accurate as you can make it before cutting down to 1Hz.

For a more accurate timing source, you can create a crystal oscillator circuit instead, or use a RTC, which usually have a 1Hz output signal.