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 :-)

  • 3
    \$\begingroup\$ You miss a few crucial parameters 1) a clock at what frequency 1 Hz, 32.768 kHz or 50 MHz ??? 2) "Good accuracy or precision" means nothing. 1% or 0.001% or 10 ppm (that's what a standard crystal does) or 1 second per month (that's about 2.6 ppm) ?? \$\endgroup\$ – Bimpelrekkie Apr 18 '17 at 11:50
  • \$\begingroup\$ Crystals take a lot less power than RC oscillators, usually, and most of the power of a clock goes in the display. You can buy cheap wall clocks that last at least a year on an AA battery. \$\endgroup\$ – pjc50 Apr 18 '17 at 12:20
  • \$\begingroup\$ @FakeMoustache The main frequency is not a problem as i'm using a binary counter.An about the precision i wants it to be as accurate as possible (10 seconds a month max). \$\endgroup\$ – Mohamed Rushdy Apr 18 '17 at 12:32
  • \$\begingroup\$ The main frequency is not a problem Not a problem but still an important part of the design. Almost all clocks use a 32.768 kHz crystal (explain why !). Dividing 50 MHz down to 1 Hz for a clock takes some power. Starting at a low frequency saves power. \$\endgroup\$ – Bimpelrekkie Apr 18 '17 at 12:39
  • \$\begingroup\$ You will need to "square up" the sinusoidal signal out of any crystal oscillator. That "Schmidt trigger" will be the power consumer. \$\endgroup\$ – analogsystemsrf Apr 18 '17 at 13:36

1) Don't use an RC oscillator if you want an accurate clock.

2) Yes, buy a crystal oscillator module.

3) Yes, buy a crystal oscillator module.


Be careful with phrases like "Precise Clock Signal", I assumed a subject like that would be about when you could use a TCXO, OCXO, or GPS disciplined clock in place of an atomic clock source. Anything over 20 ppm is a cheap and dirty low accuracy clock.

However is it possible to generate a crystal quartz oscillator without the use of a microcontroller?

Yes. A basic implementation only needs a transistor and some capacitors and resistors. There is no point in going into the implementation details here, a Google for crystal oscillator circuit will give you lots of examples of varying complexity.

As others have said, an RC is horribly inaccurate and not temperature stable. Don't even think about it for a reliable clock source.

A watch can run a 32.768 kHz quartz crystal from a tiny battery for years, so yes running for a month from an AA is possible, just make sure you use low power versions of parts and be careful not to waste power.


It's easy to make a crystal oscillator using just an inverting device. A cmos inverter in parallel with the crystal and a 1-10M resistor would work fine.

  • \$\begingroup\$ Ahem, plus capacitors and possibly output resistor. \$\endgroup\$ – Andy aka Apr 18 '17 at 12:09

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