[time-nuts] Arduino GPSDO with 1ns res TIC

[Chris Albertson]

You can buy the chip already on the PCB with supporting circuitry for
less then the price of the chip alone.  No need to go with a bare
chip.  I think the reason is that the tiny SMT package chips sell in
the millions and only a hob best would use the larger DIP through hole
package.   Look at eBay #221326355393 as an example.  The 3>71 price
includes shipping.  The advantage is __Programming__.  When you are
working on something like this you tend to want to re-program the
chips ten times an hour and it s VERY convenient to be able to leave
it plugged into the USB port on your computer.  Also for debugger a
continuous stream of data on your computer screen, maybe captured to a
file, gives yo insight to the internals.

That is the advantage of development with the Arduino vs. a bare chip,
you don't have to pull the chip to re-program it.  Yousimply change a
line of code using a text editor and click the "load" icon and a few
seconds later you are running again.  It is a very fast development
cycle.

You don't save either cost or space by using a large DIP chip the SMD
chip soldered to a PCB is about the same cost and size but also comes
with the pull up resisters, voltage regulater, standard 6-pin FTDI
interface and so on.

On Thu, Feb 13, 2014 at 6:36 AM, paul swed <paulswedb at gmail.com> wrote:
> Lars has done a very good job here and good to see the comments and
> excitement.
> Have to agree with HAL that holdover is far more than a second and I am in
> a good location with the GPS antenna at 90'. I see my 3801 go into holdover
> occasionally and its not seconds.
>
> Cheapest tinker 10 Mhz is a Xtal with a varicap diode in circuit to adjust
> frequency.
> Sub $ 5 I would guess.
>
> I was intrigued by the Arduino also and then went looking for information.
> Just about drowned in whats out there and pricing for the chip is from 99
> cents to $5.
> What bootloader X Y or Z. I like the pure chip 28 pin approach and do
> appreciate that this won't be H maser accurate.
>
> Looked at the schematic and would appreciate a more complete picture.
> Lars thats a bit more painful to do because everything has to be explicit
> in the schematic when other may build what you have shared.
> Though I have shared some ugly schematics on time-nuts. Guilty as charged.
> Regards
> Paul.
> WB8TSL
>
>
> On Thu, Feb 13, 2014 at 3:59 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
>
>>
>> [Context is cheap VCXO]
>>
>> > When used inside a GPSDO it only has to "hold over" for one second until
>> the
>> > next correction.
>>
>> Only if you have a good antenna and/or antenna location.
>>
>> I have several low cost GPS units located in far-from-ideal locations.
>>  They
>> work most of the time but often fade out for minutes at a time.
>>
>> [This is a poor setup for using the output of a GPSDO to feed other
>> measuring
>> setups, but it's great for finding corner cases in things like ntpd.]
>>
>>
>> --
>> These are my opinions.  I hate spam.
>>
>>
>>
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-- 

Chris Albertson
Redondo Beach, California