Some of you migh have seen the posts on "Digital clock" I've been wondering what's teh easiest way of generating a precise 1 Hz frequency for the clock.

An idea I heard of is dividing by 60 the AC frequency and using that instead. (or some adaptation, but the idea remains to get the pulses from it).

Any ideas?

Also, ca anyone tell me an easy way to make one with a crystal, hopefully, very much power-efficient. (I'm planning to run another one on batteries... )

Thanks a lot!

__________________
"I have not failed. I've just found 10,000 ways that won't work."
Thomas A. Edison

 

build a 32.768kHz oscillator circuit that can output CMOS or TTL levels. You can buy the complete unit or build one using a 32k crystal. Once you have that, run it into a digital divider circuit that will divide it by (2^15) then output that result and you will have a clean, precise 1Hz clock.

The 60Hz method can work (using zero crossing detectors) but since you didnt mention how "precise" you need it, the crystal is the way to go. BTW, you dont need 32k, you could use any value that is divisible by a power of 2.

I think the power company regulates the 60Hz to something like 60Hz +/- 0.001 Hz.. maybe that is good enough for you - I dont know.

 

I did a search on power line frequency variations recently and came across the following:

http://www.ornl.gov/ORNL/BTC/Restruc...NLTM200341.pdf

The article indicates the power line frequency in the U.S. is normally kept to within +/- 0.05Hz of 60Hz.

A 32Khz crystal along with a CD4060B or CD4020B 14-stage divider will give you a 0.5 second output. The 4060 includes an on-chip oscillator. 32Khz is a good choice for a portable timebase, very low power consumption, cheap & good accuracy.

 

Hi L'Apprenti Sorcier,

what's teh easiest way of generating a precise 1 Hz
frequency for the clock.

The easiest way is to get the movement from a discarded
quartz clock.
They can be found easily.
The 1 Hz signal is precise.

If you care to pick away the plastic case and cogs,
the actual unit is quite small.

Don't forget its 1.5v and uses very little current.
I doubt if you will find an easier way,
or a more economical way.

John

 

Thank you very much.

I've chosen to discard the AC input, for the reasons you told me and besides, if i'm already going for a portable one, there will be no disadvantage in using the same with the stationary.

Does anyone know where can I find more information on the 4060? schematic/example circuit/power specs.? I've never worked with it before...

About the quartz movement... How do i know what am I looking for inside the clock? Will any clock do?

Thanks again!

__________________
"I have not failed. I've just found 10,000 ways that won't work."
Thomas A. Edison

 

Here is the circuit to get a 2Hz clock signal, using the 4060. You will need to add a divide-by-2 on the end to get 1Hz (eg, flip-flop).

Attached Images

2Hzclock.jpg (10.9 KB, 1247 views)

 

Any idea of where can I get a complete specification sheet on the 4060?

__________________
"I have not failed. I've just found 10,000 ways that won't work."
Thomas A. Edison

 

I've been wondering for how long would a common battery supply a circuit like the one drawn above... any idea?

What would be the most efficient means of getting those 5V?
How much current can a 7805 give me???

Thanks!

__________________
"I have not failed. I've just found 10,000 ways that won't work."
Thomas A. Edison

 

what's a common, energy efficient flip flop to divide the pulses by two?

Thanks

__________________
"I have not failed. I've just found 10,000 ways that won't work."
Thomas A. Edison

 

half of a CD4013 or 74HC74. Connect the Q/ output back to the D input to make a toggle flip-flop.

for the CD4060 datasheet:
http://www.ee.washington.edu/stores/...000/cd4060.pdf

 

Thanks!

I'll try that..

__________________
"I have not failed. I've just found 10,000 ways that won't work."
Thomas A. Edison

 

Does anyone have a diagram for the 4013 divider? what's the difference between that one and the 4017?

I'm wondering how should i use it to divide by two?

__________________
"I have not failed. I've just found 10,000 ways that won't work."
Thomas A. Edison

 

You mention a 4017. If you have one you can use that as a divide-by-2.
Connect the '2' output to Reset. When it counts, it will go 0 > 1 >2 which will rest it back to 0, So effectively it will count 0 > 1 > 0 > 1 etc. Take your output from either the 0 or the 1 to get the divide-by-2.