Precise 100Hz or 1kHz Pulse without IC or Crystal?

wayneh

Joined Sep 9, 2010
17,152
Precise enough to use for a digital clock... I sorta want to build an all transistor clock but do not want to tap into main AC or using crystal
I think an LC tank will give more precision than, for instance, a 555 timer is capable of. Take care in selecting the components to minimize temperature effects and drift. I’m not sure what precision is achievable.
 

be80be

Joined Jul 5, 2008
2,051
I'm looking a a 60 Hz oscillator it very close till i touch it I was just wondering the same how to make it stable

But Mine is using 2 resistors and cap and 2 nand gates It's nice 60 Hz till i touch it. lol
 

MrChips

Joined Oct 2, 2009
23,240
Precise enough to use for a digital clock... I sorta want to build an all transistor clock but do not want to tap into main AC or using crystal
Precision is normally quoted in terms of percent error or drift.
For "precise" timing applications, a quartz crystal oscillator is commonly used.
Accuracy is of the order of 10ppm for a typical crystal oscillator.
1000ppm = 0.1%
100ppm = 0.01%
10ppm = 0.001%
1ppm = 0.0001%

There are 1,036,800 seconds in 12 days.
Therefore a crystal oscillator with 10ppm drift will drift by about 10 seconds in 12 days.

If you want long term accuracy for a time-of-day clock, use the 50Hz or 60Hz line frequency.
The short term stability of line frequency is about ±0.03%. However, the total number of cycles is corrected daily so that long term error is practically zero.

You will discover that any RC oscillator will result in very unsatisfactory time-keeping.
 

Ohmlandia

Joined Mar 2, 2020
32
Get a time signal broadcast receiver on 60kHz, and decode its output. That way you only have to design and build the display, and your clock will be accurate to seconds for thousands of years.
 

DickCappels

Joined Aug 21, 2008
7,272
The guy who would come over and tune my father's piano used a set of tuning forks. Ancient battery powered watches used a transistorized "electric" tuning forks. You could hold the watch up your ear and hear the tuning fork.



What's wrong with using quartz?
 

MrAl

Joined Jun 17, 2014
8,149
Precise enough to use for a digital clock... I sorta want to build an all transistor clock but do not want to tap into main AC or using crystal
Yeah forget it. Wall clocks require very long term accuracy unless you dont mind resetting it every week or so.
Even regular crystals are not really good enough for wall clocks. You need a temperature compensated crystal oscillator. You can get real time clock boards and chips that do this.

If you use an LC tank you have to temperature compensate it with thermistor(s). It is a royal pain in the neck and it's only as good as you can get it. Probably have to reset the clock once per month.
Might be better off with a pendulum clock (ha ha).

Sync up to WWV.
 

MrChips

Joined Oct 2, 2009
23,240
How are you going to power the clock?
Is the clock going to be located permanently indoors?
There is so much 60Hz AC signal being radiated that you can pickup the signal without a direct connection.

You can build a solar powered clock. I never completed mine. I had laid out the PCB but never got around to having it fabricated.
It would keep track of solar time and was designed to run for 1000 years without requiring adjustment.
 

atferrari

Joined Jan 6, 2004
4,279
I think an LC tank will give more precision than, for instance, a 555 timer is capable of. Take care in selecting the components to minimize temperature effects and drift. I’m not sure what precision is achievable.
I agree. The very first working circuit I built was a CW xmtr modified to emit AM in the 40 and 80 m bands. The VCO had an LC tank with a classic 365 pF variable capacitor. Made it heavy, mechanically (extremely) stable and was furiously shielded. Worked like a gem.
 
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