1Hz timebase

[catcat]

How do I get a precice 1hz timebase for a digital clock. Even if its a sine wave generator, I can probably use a comparator or schmitt trigger to turn it to a square wave. I was wondering if you use an amplifier with the feedback component a quartz crystal, will it oscilate the resonant frequency of the crystal? (the problem is how to turn it to 1hz)

 

[Nigel Goodwin]

Just use digital dividers, if it's mains operated just divide down from the mains frequency, or use a 32KHz clock crystal and divide down from that - it's a well known (VERY old) technique.

 

[catcat]

Its Battery powered, the digital divider might work. But how to make the crystal resonate?

 

[Rolf]

How do I get a precice 1hz timebase for a digital clock. Even if its a sine wave generator, I can probably use a comparator or schmitt trigger to turn it to a square wave. I was wondering if you use an amplifier with the feedback component a quartz crystal, will it oscilate the resonant frequency of the crystal? (the problem is how to turn it to 1hz)

This is a good read on the subject:
**broken link removed**

Here is another one:
https://www.rentron.com/at89c205.htm

 

[Nigel Goodwin]

Its Battery powered, the digital divider might work. But how to make the crystal resonate?

In a crystal oscillator circuit!.

 

[catcat]

How to make one? (And it should oscilate the resonant frequency of the crystal.)

 

[audioguru]

How to make one?

Haven't you heard about looking for circuits in Google??

 

[William At MyBlueRoom]

A 32768Hz crystal and a CD4060 will give you 2Hz. A simple flip / flop will give you the 1Hz you're after.

**broken link removed**

 

[Hero999]

Except that circuit uses a 4.194304MHz crystal.

You could try this circuit

**broken link removed**

http://www.mcamafia.de/nixie/ncp_en/ncp.htm

Other examples are:
**broken link removed**
http://www.kpsec.freeuk.com/components/cmos.htm#4060

 

[audioguru]

Improooooooooved.
Sounds like an ad on TV.

 

[Roff]

Wanna see something funny? Do a Google search for "1 Hz time base 32768".
Caveat: I'm in the US. I'm not sure if the results are the same worldwide. Does Google know what country you're in, and tailor the results accordingly?

 

[RODALCO]

I can draw one up for the 4.194304 MHz one.

Not sure if you can get the ic anymore or cascade two 4060's.
You need to divide by 22 to get one Herz from that one.

But they are very accurate.

scl 1444 used to be built in the German Maxirex BQT and QTT timers from the late 80's.
I salvaged quite a few of those for the accurate timing module in them which drives the seconds stepper motor for the clock.
Luckily i work for the powerboard so a good supply was always there when the back up nicads failed these clocks were just dumped in the bin.

By removing the motor wires and putting a 470Ω to 1 kΩ resistor across the terminals, then taking the defect nicad out and replacing it with a 100 µF capacitor and across it a red LED. and converting it from 230 Volts AC to 12 or 5 volts dc it can drive a 4 N 35 opto and provide direct 1 second clock pulses or via a schmitt trigger if required.

I can draw up a schema if anyone is interested.

 

[Hero999]

You could always buy a cheap analogue clock module and use the circuit to generate the pulse.

 

[Rolf]

Wanna see something funny? Do a Google search for "1 Hz time base 32768".
Caveat: I'm in the US. I'm not sure if the results are the same worldwide. Does Google know what country you're in, and tailor the results accordingly?

Google only searches in the languages you specify. Since I am multy lingual I have it search in five. Of cause I am not fluent in five.

 

[on1aag]

1 Hz timebase.

1 Hz timebase.

 

[RODALCO]

Thanks for that circuit on1aag.

I had a similar schema somewhere and couldn't find it with the 4521 IC in it.

 

[Klaus]

1 Hz timebase.

I built that one years ago for a LED clock. The circuit works fine but I found home built crystal oscillators lack long term accuracy if one is finicky about keeping time.

No matter how accurately I trimmed the capacitor to get the oscillator running on the precise frequency, a few weeks later it would be out again.

These crystals are temperature sensitive, keep that in mind. I guess they could be housed in a crystal oven but that needs power to run which is not an option for a battery powered clock.

A much better idea is the mains frequency derived 1Hz pulse, they take great care at the power station (in large cities) to have the frequency average out precisely over 24 hours.

What really bugs me is a $5.- digital LCD wrist watch that I have keeps a much better time than the fancy LED clock with crystal oscillator I built.
Perhaps it is because the wrist watch is always at body temperature as I only take it off while having a shower.

 

[Nigel Goodwin]

A much better idea is the mains frequency derived 1Hz pulse, they take great care at the power station (in large cities) to have the frequency average out precisely over 24 hours.

Doesn't Australia have a 'National Grid' like the UK?, perhaps due to the size of the country it's not practicable? - but in the UK all power stations are syncronised together, so all mains supplies are accurate.

What really bugs me is a $5.- digital LCD wrist watch that I have keeps a much better time than the fancy LED clock with crystal oscillator I built.
Perhaps it is because the wrist watch is always at body temperature as I only take it off while having a shower.

As you say, the constant temperature probably helps?, but did you use a 32KHz crystal for your clock?, those are the most accurate ones for such use.

 

[catcat]

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.

I now have a 555 timer with trompot adjustment but I cant get it right!

 

[catcat]

A much better idea is the mains frequency derived 1Hz pulse, they take great care at the power station (in large cities) to have the frequency average out precisely over 24 hours.

Its battery powered.