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

Chris Albertson albertson.chris at gmail.com
Thu Feb 13 11:34:37 EST 2014

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.

You will need one of the larger chips for this.   Closer to $5 than 0.99

> 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.

The "boot loader" is built into the Arduino IDE.  It's a pull down
from the Tools
menu.  Just select "Tools->Burn Bootloader" and it works.  But you should never
have to do this.  All Arduinos ship with a bot loader and  preloaded example
program to blink an LED.

Don't let at the information of the Internet about this overload you.  All you
need to know, can be found from the "help" menu item.

If you remove all of Lars' data logging and mode setting (debug) stuff this is a
very short and simple bit of software.

> Looked at the schematic and would appreciate a more complete picture.

There are only two ICs and he does not use even half
of the pins.    I doubt that it is critical that you even use the same
divider chip.
He does leave out the details about th switches on lines A1..A5.  You
can see where thet
are read and what is done with the data but it would be nice to see a schematic.

There is certain;y enough information posted to get one of these working.

My plan is to build one and make changes one step at a time.  As I said
there is enough information to do that.

>> [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'll use whatever is in the "junk box" for initial testing, then later
the Rb oscillator.

Chris Albertson
Redondo Beach, California

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