Precise Clock Signal

Thread Starter

Mohamed_Rushdyy

Joined Nov 4, 2016
18
Hi Guys
I'm working on a project where i try to make a normal clock.Everything is finished and ready except for the main signal coming from the oscillator.
I'm making a relaxation oscillator of course but i'v so many questions...
FIRST : About the RC oscillator in general:
i want the clock to be very precise and accurate so is the RC circuit will give me that precision...?
And how about the temperature stability,Will the RC be good in this condition as i know that the resistors are very bad at temp. stability...???
Finally what components should i use in the design,Should i use Op-Amps or MOSFETs or BJTs...? i'm asking here from the power consumption point of view...
SECOND : About the Crystal Oscillators
I know that the crystals are very accurate and maintain a very good temp. stability,However is it possible to generate a crystal quartz oscillator without the use of a microcontroller.And if so what is the best configuration that i should use in that design...
And how about the power consumption does the crystal takes more power than the normal RC circuit if they produce the same frequency...
THIRD :
Is it possible to make a clock with a good precision with the use of ONE AA battery and last for about 3 months min or i'm dreaming about this...?

I hope i didn't annoy you with that much questions and Thanks in Advance :):)
 

GopherT

Joined Nov 23, 2012
8,009
Hi Guys
I'm working on a project where i try to make a normal clock.Everything is finished and ready except for the main signal coming from the oscillator.
I'm making a relaxation oscillator of course but i'v so many questions...
FIRST : About the RC oscillator in general:
i want the clock to be very precise and accurate so is the RC circuit will give me that precision...?
And how about the temperature stability,Will the RC be good in this condition as i know that the resistors are very bad at temp. stability...???
Finally what components should i use in the design,Should i use Op-Amps or MOSFETs or BJTs...? i'm asking here from the power consumption point of view...
SECOND : About the Crystal Oscillators
I know that the crystals are very accurate and maintain a very good temp. stability,However is it possible to generate a crystal quartz oscillator without the use of a microcontroller.And if so what is the best configuration that i should use in that design...
And how about the power consumption does the crystal takes more power than the normal RC circuit if they produce the same frequency...
THIRD :
Is it possible to make a clock with a good precision with the use of ONE AA battery and last for about 3 months min or i'm dreaming about this...?

I hope i didn't annoy you with that much questions and Thanks in Advance :):)

RC relaxation oscillators are not accurate enough for a clock.

A crystal oscillator can be made with a CD4060 chip, 2 capacitors and a 32.768 kHz crystal.

Add a flip flop chip to the CD4060 chip's output and you have nice square wave with 1Hz output.
 

AnalogKid

Joined Aug 1, 2013
10,987
Resistors can be *very* accurate and stable. The main problem with R-C oscillator precision is the capacitor. Compared to that, a crystal oscillator as a purchased component is cheap. A 32.768 kHz "crystal" (actually, a tuning fork) is very low cost and the central part of many clock circuits. For better accuracy, use a real quartz crystal such as 2.097 MHz and divide it down with binary counters.

For a good compromise between accuracy and power consumption, get a battery-powered clock and remove the small circuit board inside. There are several threads on this and other fora that describe this. Those circuits are designed to run for many months on one AA or AAA cell.

Where are you located?

ak
 

Thread Starter

Mohamed_Rushdyy

Joined Nov 4, 2016
18
Resistors can be *very* accurate and stable. The main problem with R-C oscillator precision is the capacitor. Compared to that, a crystal oscillator as a purchased component is cheap. A 32.768 kHz "crystal" (actually, a tuning fork) is very low cost and the central part of many clock circuits. For better accuracy, use a real quartz crystal such as 2.097 MHz and divide it down with binary counters.

For a good compromise between accuracy and power consumption, get a battery-powered clock and remove the small circuit board inside. There are several threads on this and other fora that describe this. Those circuits are designed to run for many months on one AA or AAA cell.

Where are you located?

ak
Thanks for your help you really made things clear to me...
About the battery thing i don't know about this yet as i'm having a problem converting the 1.2~ volts to 5 volts to be used in the digital components my question here was theoretical if i can use the oscillator on that small voltage...And about the designs of the "Battery-Powered" clocks i'v seen many of them but it contains many components that i can't get for many reasons so i try to do it with the simplest components that i can reach...
 

AnalogKid

Joined Aug 1, 2013
10,987
Many commercial products use ASICs (Application-Specific Integrated Circuit), chips custom designed for one specific task. Impossible to get unless you want 10,000 or so. Also, products use small microcontrollers like the PIC or AVR programmed to do the task. You can buy the same part, but without the firmware it won't do anything. Some PIC parts are designed with very low operating current for battery-powered tasks.

Very few commercially available ICs will operate at 1.2 V. The analog clock I mentioned has an ASIC .

ak
 

crutschow

Joined Mar 14, 2008
34,285
Standard CD4000 CMOS circuits can operate down to 3V.
I suggest you use those and one 3V lithium battery for power.

What are you using for the clock display?
 

ian field

Joined Oct 27, 2012
6,536
Hi Guys
I'm working on a project where i try to make a normal clock.Everything is finished and ready except for the main signal coming from the oscillator.
I'm making a relaxation oscillator of course but i'v so many questions...
FIRST : About the RC oscillator in general:
i want the clock to be very precise and accurate so is the RC circuit will give me that precision...?
And how about the temperature stability,Will the RC be good in this condition as i know that the resistors are very bad at temp. stability...???
Finally what components should i use in the design,Should i use Op-Amps or MOSFETs or BJTs...? i'm asking here from the power consumption point of view...
SECOND : About the Crystal Oscillators
I know that the crystals are very accurate and maintain a very good temp. stability,However is it possible to generate a crystal quartz oscillator without the use of a microcontroller.And if so what is the best configuration that i should use in that design...
And how about the power consumption does the crystal takes more power than the normal RC circuit if they produce the same frequency...
THIRD :
Is it possible to make a clock with a good precision with the use of ONE AA battery and last for about 3 months min or i'm dreaming about this...?

I hope i didn't annoy you with that much questions and Thanks in Advance :):)
Take a look at catalogues from crystal manufacturers - many have a collection of example circuits in the back pages.

Murata are well known for their ceramic resonators and sample circuits - but I'm not sure about crystals.
 

Thread Starter

Mohamed_Rushdyy

Joined Nov 4, 2016
18
Standard CD4000 CMOS circuits can operate down to 3V.
I suggest you use those and one 3V lithium battery for power.

What are you using for the clock display?
I didn't finally decide yet but i think i will use the normal 7-Segment display...If you know something less power consuming i'll be happy to hear about it...
 

ian field

Joined Oct 27, 2012
6,536
I didn't finally decide yet but i think i will use the normal 7-Segment display...If you know something less power consuming i'll be happy to hear about it...
Manufacturers like Holtek make MCUs entirely dedicated to driving class only LCDs for minimum possible power consumption.

HD44780 style LCD modules aren't too bad as long as you don't use the backlight LED.
 

GopherT

Joined Nov 23, 2012
8,009
I didn't finally decide yet but i think i will use the normal 7-Segment display...If you know something less power consuming i'll be happy to hear about it...
LED displays are power hogs. Avoid them unless you only want them to display for a few seconds every time you push a button and allow the non-display circuitry to run in the background.
 

GopherT

Joined Nov 23, 2012
8,009
Remember LED wristwatches.

Mine has a light-weight Spring with a weight on it that allowed it to turn on for 3-seconds when you hold your arm in font if your face. It was the first thing I ever inherited. Mine is less scratched than this stock image but it still works.
image.jpeg
 

ian field

Joined Oct 27, 2012
6,536
Mine has a light-weight Spring with a weight on it that allowed it to turn on for 3-seconds when you hold your arm in font if your face. It was the first thing I ever inherited. Mine is less scratched than this stock image but it still works.
View attachment 125080
Recently found a Radio Shack LED calculator dropped on the ground near some recycling bins.

It uses a PP3 9V battery (not good!) But it has a proper mechanical on/off switch.

Most LCD calculators have push button on/off that get knocked in my jacket pocket - the battery is *ALWAYS* flat when I go to use it.

Had a solar only LCD calculator without any on/off control - for some reason it just irritated me..............
 
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