1Hz timebase

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catcat said:
I want no adjustments/variable capacitors because:
1: I dont have good variable caps and cant get to them
2: I want it to precosely divide the crystals oscillation so tha it will just work precisely.
Click to expand...

A crystal needs trimming to be precisely on frequency, one obvious variable is the exact method of construction used - the differences in capacitance will alter the crystal frequency.

The only way to do it without adjustment would be to buy a pre-built and pre-aligned module.

If you're trying to do it with a 555, I'm not suprised you can't adjust it?, it's no where near stable enough - a crystal version without being trimmed at all would be many times closer to being right!.
 
The gentleman at AADE.com offers a small 1-ppm 10-MHz TCXO board for about $15, though I don't believe it's pictured anywhere on his web site, and he calibrates it to his Rubidium frequency standard before shipping.

You could also use a tiny 8-pin PIC microprocessor and 20-MHz crystal to provide a 1-Hz clock output accurate to within plus or minus 200-nsecs per second (6.3 seconds per year) not including temperature drift or crystal aging by utilizing "software trimmer capacitor" program code.

Mike
 
If you want a really accurate clock hook up a cheap GPS. You'll need a micro and a serial port, but should keep really accurate time anywhere in the world.
 
The accuracy depends on the grade of the crystal, often higher frequency crystals are manufcatured to a higher standard but this in't always the case. I have a cheap and nasty LCD clock built into a shaving mirror, it must loose 10 or so seconds a day so after a few months its nearly an hour out! I think the crystal is faulty so when I get round to it I'll replace it.
 
I have a picture of the clock and an idea of a crystal oscilator that worked wiht a capacitor instead of a crystal (Idont have crystals yet). And how do I divide a Khz clock crystal to 1Hz With room for only 2 or 3 more ic's?
 

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May I just say, that's probably the worst build circuit I've EVER seen!.

There are plenty of crystal oscillator circuits about, for this type of use they generally use a CMOS or TTL gate - your opamp 'circuit' wouldn't work, and doesn't appear to be complete either?.
 
How did you manage to get that wire bunch to work !!

Must be very hard to trace for faults and reading the actual segments for the clock.

But good effort, although now it needs tidying up.
 
Nigel Goodwin said:
There are plenty of crystal oscillator circuits about, for this type of use they generally use a CMOS or TTL gate - your opamp 'circuit' wouldn't work, and doesn't appear to be complete either?.
Click to expand...


I dont exactly understand.
 
How do you make it work?

(And yes, that clock isnt extrmely pretty, but it works great (exept the timinng).)
 
catcat said:
How do you make it work?
Click to expand...

You wouldn't really, an opamp isn't something you would use for a crystal oscillator. However, have a look here **broken link removed** which as well as logic crystal oscillators shows exactly what you're looking for.

(And yes, that clock isnt extrmely pretty, but it works great (exept the timinng).)
Click to expand...

Do you buy all your wire pre-cut?, and don't own a pair of cutters?
 
there are some things I dont understand there.


I got a big spool of wire and a good cutting/stripping tool.
 
catcat said:
there are some things I dont understand there.


I got a big spool of wire and a good cutting/stripping tool.
Click to expand...

Just wondering why all your wires are so long?
 
Nigel Goodwin said:
May I just say, that's probably the worst build circuit I've EVER seen!.
Click to expand...
Me, too. What a mess! I didn't see it before.
It has about 1 dozen old TTL ICs. It looks like a circuit from 1975 and I expected it to have Nixie tubes instead of LEDs.
 
I has all CMOS ic's and they are brand new.

Lets not change the subject.
 
Last edited:
Hey guys, it's hard to keep things neat on those wireless breadboards. Here's what one of my early clock projects looked like. Pretty sad, huh?

Mike
 

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Hi
There is another method io get more accurate 1Hz by using OEM GPS receiver most of OEM GPS receiver provide one pulse per second output and it is TTL you can use it directly
 
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