[time-nuts] 1 pps correction

[Chris Albertson]

On Sat, Apr 7, 2012 at 11:45 AM,  <EWKehren at aol.com> wrote:
> Chris
>  do you or any one else have a micro controller and code for  such an 8 pin
> solution? The rest I would know how to do.

That is what I wrote about earlier, few people have the technical
skill to do every part of a design.   No I don't have a finished part
but it's a one hour job.  The software would work like this:

1) Read a line of text from serial port
2) Is it a sawtooth correction message?
3) If "no" go to #1 above

4) Extract value from message
5) Multiply value by a scale factor so it "fits" best inside the DAC's
10 or 8 bit range
6) Send the scaled value to the DAC pin.
7) go to #1.

In "C" you use while loops rather than a go toe but it's the same thing.

A good way to develop a prototype would be to use an Aruino.   It's a
$40 development system so it is about 20 times over priced but it is
VERY easy to use and set up so non-programmers can learn to use it
quickly.  Once the software works on the Arduino it is not hard to
move to the Tiny AVR (which by the way cane very tiny, ilk an 8-pin
SMD chip.)





> Bert Kehren
>
>
>
> In a message dated 4/7/2012 12:12:40 P.M. Eastern Daylight Time,
> albertson.chris at gmail.com writes:
>
> The  simplest way to do this is to use a "standard" GPS and let if
> drive a  GPSDO.  Yes you can try and build a copy of a T-bolt but how
> many  engineering ours do you think Trimble spent on that?  Well over a
> man  year I'd say and few people have the range of skills needed to do
> it all  themselves.
>
> If you want to use the sawtooth data in the GPSDO then  you'd need a
> one of those very small 8-pin micro controllers.  It  could "tap" the
> serial line and listen for the sawtooth correction and then  output a
> voltage on an analog pin.   The sawtooth correction does  not change
> very fast so the bandwidth is low enough for something like an  AVR or
> PIC.  This uP would have only one function so the software  would be
> easy
> I think you'd use the analog sawtooth voltage to slightly  bias the
> phase detector.
>
>
>
> On Sat, Apr 7, 2012 at 3:59 AM,  Attila Kinali <attila at kinali.ch> wrote:
>> On Sun, 1 Apr 2012  19:10:59 +0000
>> shalimr9 at gmail.com wrote:
>>
>>> It seems  to me that if standalone GPS timing receivers used a VCXO
>>> instead  of a fixed frequency clock, the cost delta would not be that
>>>  significant, and they too could avoid the need for sawtooth  correction.
>>
>> Not really. You'd need a low noise, low DNL, high  resolution DAC to
>> stear the VCXO. Analog electronic costs considerably  more than a tiny bit
>> of software and eats a lot more  power.
>>
>> Maybe you can get away with using one of the Silicon  Labs programmable
>> oscillators instead of a VCXO and a DAC. But IIRC  they only have a
>> frequency setting, no phase setting, so you need some  way to fix the
>> phase offset.
>>
>>        Attila  Kinali
>>
>>
>> --
>> Why does it take years to find the  answers to
>> the questions one should have asked long  ago?
>>
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>
> --
>
> Chris Albertson
> Redondo  Beach,  California
>
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-- 

Chris Albertson
Redondo Beach, California