Groups > sci.electronics.design > #452098

Re: Low Frequency 3rd Overtone Crystal Osc

From	rickman <gnuarm@gmail.com>
Newsgroups	sci.electronics.design
Subject	Re: Low Frequency 3rd Overtone Crystal Osc
Date	2017-03-16 04:40 -0400
Organization	A noiseless patient Spider
Message-ID	<oaditf$esk$1@dont-email.me> (permalink)
References	(10 earlier) <oaaugg$2rv$1@dont-email.me> <oabqrl$32p$1@dont-email.me> <65bkccttgadbrtf4j9ojv7s5lbjp19oecv@4ax.com> <oadcgn$sqo$2@dont-email.me> <fuekcct0911kumd3v1hmlek5kuvttvp6qa@4ax.com>

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On 3/16/2017 3:28 AM, upsidedown@downunder.com wrote:
> On Thu, 16 Mar 2017 02:51:41 -0400, rickman <gnuarm@gmail.com> wrote:
>
>> On 3/16/2017 2:20 AM, upsidedown@downunder.com wrote:
>>> On Wed, 15 Mar 2017 12:44:10 -0400, rickman <gnuarm@gmail.com> wrote:
>>>
>>>>>
>>>>>
>>>>> This may be a heresy:
>>>>>
>>>>> There are plenty of small ARM Cortex-M chips with built-in
>>>>> counter-timers. Get one of them with a decent crystal (say in the range of
>>>>> 5 to 20 MHz) and divide from it with the built-in timer. The cost
>>>>> will be just some dollars for the components.
>>>>>
>>>>> A small Cortex evaluation unit can be had for some tens of dollars,
>>>>> and there are the crystal and board built-in, together with some
>>>>> means of getting the code in.
>>>>
>>>> Thanks for the suggestion, but that does not fit the problem space.  The
>>>> FPGA board I am prototyping with has an oscillator on board, just not a
>>>> multiple of 240 kHz.  This is a very low power design and every ARM type
>>>> CPU I have seen will consume mAs of current with the high speed crystal
>>>> controlled clock.
>>>
>>> How about a free running CPU clock running at a few MHz and a crystal
>>> in 0.5 to 1.5 MHz range generating an interrupt about every
>>> microsecond. The interrupt updates the NCO (numerical controlled
>>> oscillator) 16 to 32 bit phase accumulator and some bits are written
>>> to the output pins. The rest of the time, the processor is kept in  a
>>> low power sleep mode. If sin/cos output is needed, insert a sine
>>> lookup table between the phase accumulator and output pins.
>>> These should not require many instructions, so the power consumption
>>> should be low.
>>
>> I appreciate the suggestion, but why all the complexity?  If I have a
>> crystal creating a clock, I don't need the CPU.  What you described is
>> way more power and complexity than needed.
>
> I understood that you originally had problems ordering a crystal for
> the exact integer multiple of 120 kHz. The NCO principle allows you to
> generate any frequency from an other frequency, which doesn't have to
> be harmonically related, as long as the Nyquist criterion is followed.

That's not entirely correct.  To get an exact value the reference 
frequency and the target frequency must be related by the ratio of two 
integers.  Fclk = Fref * NCOstep / NCOmodulus where NCOstep is the phase 
increment and NCOmodulus is the modulus of the phase accumulator.


> Regarding timepiece crystals, NT cut crystals have been made for 32
> and 131 kHz, while DT cut has been used for 272 and 327 kHz. So if you
> want 240 or 480 kHz, look for DT cut crystals. How many do you need ?
> Some small crystal house might even make single crystals, but the cost
> can be high.

I'd be happy with a handful, 5 to 10.  I've contacted crystal 
manufacturers and they don't want to make anything for me that isn't a 
standard item.


> I do not know about DT cut, but I have ordered AT cut crystals in
> units of one for each frequency.

I can do without the crystal I think.  I can use 32.768 kHz as my 
reference.  I can buy real time clock chips with temperature 
compensation and a programmable output intended for a processor 
interrupt.  That output can be set for 1 second or other rates and used 
to time an LC oscillator.  The LC oscillator can be trimmed with a 
varactor from the frequency measurement.  I may start testing this 
tomorrow.

-- 

Rick C

Thread

Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-08 17:51 -0500
  Re: Low Frequency 3rd Overtone Crystal Osc Jon Elson <jmelson@wustl.edu> - 2017-03-08 17:04 -0600
    Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-08 19:57 -0500
    Re: Low Frequency 3rd Overtone Crystal Osc Robert Baer <robertbaer@localnet.com> - 2017-03-10 00:01 -0800
  Re: Low Frequency 3rd Overtone Crystal Osc dagmargoodboat@yahoo.com - 2017-03-08 18:02 -0800
    Re: Low Frequency 3rd Overtone Crystal Osc John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-03-08 18:13 -0800
      Re: Low Frequency 3rd Overtone Crystal Osc Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-09 09:11 -0500
        Re: Low Frequency 3rd Overtone Crystal Osc John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-09 08:14 -0800
          Re: Low Frequency 3rd Overtone Crystal Osc Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-09 11:24 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-11 11:20 -0500
      Re: Low Frequency 3rd Overtone Crystal Osc Neon John <no@never.com> - 2017-03-09 16:24 -0500
        Re: Low Frequency 3rd Overtone Crystal Osc John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-03-09 14:23 -0800
          Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-09 18:16 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc Neon John <no@never.com> - 2017-03-13 19:59 -0400
            Re: Low Frequency 3rd Overtone Crystal Osc John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-03-13 17:29 -0700
              Re: Low Frequency 3rd Overtone Crystal Osc bill.sloman@ieee.org - 2017-03-13 18:43 -0700
            Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-13 21:54 -0400
      Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-10 10:15 +0000
    Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-08 22:33 -0500
      Re: Low Frequency 3rd Overtone Crystal Osc o pere o <me@somewhere.net> - 2017-03-09 15:39 +0100
      Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-09 09:41 -0500
        Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-09 09:43 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-09 11:17 -0500
            Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-09 20:42 -0500
              Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-09 20:55 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc piglet <erichpwagner@hotmail.com> - 2017-03-11 07:37 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-11 03:15 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc piglet <erichpwagner@hotmail.com> - 2017-03-11 09:52 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-11 08:54 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-11 09:00 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc Jasen Betts <jasen@xnet.co.nz> - 2017-03-11 23:58 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-11 22:13 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-13 11:20 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-13 11:47 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-13 23:44 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-03-13 15:55 -0700
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-13 19:58 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc Jasen Betts <jasen@xnet.co.nz> - 2017-03-14 04:48 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-14 13:37 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-03-14 22:29 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-14 20:59 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-03-15 10:40 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-15 12:44 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-16 08:20 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-16 02:51 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-16 09:28 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-16 04:40 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc bill.sloman@ieee.org - 2017-03-16 05:09 -0700
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-16 12:47 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-17 00:22 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-16 19:14 -0400
    Re: Low Frequency 3rd Overtone Crystal Osc John S <Sophi.2@invalid.org> - 2017-03-13 05:51 -0500
      Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-13 08:39 -0400
  Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-09 21:09 -0500
  Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-09 20:15 -0600
    Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-09 23:36 -0500
      Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-10 19:02 -0600
        Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-11 01:15 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-11 11:04 +0200
          Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-11 09:31 +0000
      Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-11 09:15 +0000
        Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-11 10:50 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-11 16:46 +0000
        Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-11 15:36 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-11 23:50 +0000
            Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-11 17:59 -0600
              Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-12 08:44 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-12 20:23 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-13 12:21 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-14 03:30 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-14 20:50 +0000
  Re: Low Frequency 3rd Overtone Crystal Osc Robert Baer <robertbaer@localnet.com> - 2017-03-09 23:57 -0800
    Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-10 05:51 -0500
    Re: Low Frequency 3rd Overtone Crystal Osc Mike Jones <mikejones@gmail.com> - 2017-03-10 06:03 -0600
  Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-10 15:34 +0200
  Re: Low Frequency 3rd Overtone Crystal Osc Tim Wescott <tim@seemywebsite.really> - 2017-03-11 12:51 -0600
    Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-12 00:33 +0200
      Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-12 01:00 -0500
        Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-12 10:45 +0200
          Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-12 18:32 -0400
    Re: Low Frequency 3rd Overtone Crystal Osc Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-13 11:26 -0400

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