32768 KHz oscillator 3v through hole?

Discussion in 'General Electronics Chat' started by PickyBiker, Feb 19, 2016.

  1. PickyBiker

    Thread Starter Member

    Aug 18, 2015
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    32768 KHz is a very common clock frequency for a number of applications so I thought I would be able to find an IC that would run at 3-3.6V in a through hole package. As it turns out, I couldn't find one at mouser or digikey.

    Anyone got a design for a xtal controlled 32768 KHz clock generator using only 3 - 3.6V parts and through hole only? The crystals I have are watch crystals with 20 ppm accuracy.
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    A CD4060 will take a watch crystal and has on-chip dividers to divide down to 2Hz. You add a flip-flop and you have 1 second pulses.
    Very wide supply voltage range. Note that the CD4040 (on the same datasheet) does not have the on-chip oscillator circuitry to support your watch crystal. Get the 4060.


    https://www.fairchildsemi.com/datasheets/CD/CD4060BC.pdf
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    ON ebay or Banggood, you can find real time clocks ("RTC") that put out an accurate 32768 Hz signal. You do not need an MCU to run them. The prices are about $1 to $2 each, and they include a battery. Here is just one of many examples:
    http://www.ebay.com/itm/1Pcs-DS3231...629474?hash=item51df0ea362:g:ccAAAOSw5dNWn8a7

    You don't have to use all of the pins. Just what you need. You can also take a watch crystal and 2 small capacitors and make a low power oscillator for an MCU. The RTC have a temperature correction algorithm built in and are more stable.
    John
     
  4. dannyf

    Well-Known Member

    Sep 13, 2015
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    Fairly easy: get an oscillator and you are done.

    I often use an oscillator / counter for that - HC4060 for example - to generate a series of frequencies, from 32Khz, or from higher frequencies and dividing it down to 0.5/1Hz output.

    Or you can get a maxim part with a crystal built-in.
     
  5. hp1729

    Well-Known Member

    Nov 23, 2015
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    That is 32.768 KHz, right? Not 32768 KHz.
     
    PickyBiker likes this.
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    don't be snarky. He said it was a watch crystal. Do you know of any 32MHz watch crystals?
     
  7. PickyBiker

    Thread Starter Member

    Aug 18, 2015
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    1
    First, yes, it is 32.768 KHz , not 32768KHz. Sorry about that.

    This clock generator will be the 32.768 KHz source for a radio IC so all I need is that frequency, I don't need to divide it down to anything else.

    jpanhalt pointed to some eBay parts that should work. I will just need to verify the 32k output pin is actually the precise 32.768 KHz I need for the radio. I like the fact that it is much more accurate than the xtals I have and temperature compensated too. It also works on the I2C bus that I use to control the radio and it will work on 3.3V.
     
  8. dannyf

    Well-Known Member

    Sep 13, 2015
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    Yes, if they used the real maxim part.

    I have a few and I can tell you with high degree of confidence that 1) they are very accurate; and 2) they are not genuine maxim parts.
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    Certain CMOS families will work down to that voltage (just about) a common watch crystal oscillator used on older PC motherboards is based on the 4069 hex inverter. The basic circuit turns up a lot on website blogs etc.
     
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