[time-nuts] GPSDO Alternatives

Bob Camp lists at rtty.us
Thu Dec 6 17:43:45 UTC 2012


There are at least 500 different processors out there that could / might
work in a GPSDO. I can think of 40 or more families of parts one could look
at from more than a dozen companies. That's just counting the majors, and
not getting into any of the smaller outfits. It's also not including any of
the stuff that's likely overkill for the job. 

If you head off into ARM land, there are a number of hobby oriented projects
out there. Raspberry PI is one, there are *many* others in the sub $50 price
range. One of many is the 


The board is somewhere from free (sit in a room for 2 hours) to $13 (buy it
from distribution). It's got a full blown debugger and it will interface
with Adruino shields. It also has free software and a free RTOS to go with
it. For those who like data logging, it's set up for a SD card. Price wise -
at least as cheap as any Arduino I've seen. (... and it's a dual CPU card,
if you re-use the debugger CPU). 

No I don't know if that's the right card or not to use. I'm only tossing it
up as another example of what might be used. It is representative of many
boards one might consider. 

The obvious gotcha here is that there are *way* too many choices rather than
too few. I don't know of any boards or CPU's that will do the job without
some "glue" externally. CPU's have a following, just as brands of cars do.
This has turned into a Ford / Chevy debate in the past. That doesn't move
anything forward. There really is no right or wrong, just a lot of personal
preferences with a lot of emotion involved. 

Until a group of people decide they want to do this, I'd leave the CPU
choice wide open. Once you have a willing group, let them work with what
ever they are comfortable with. The bigger decisions and issues are


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Keenan Tims
Sent: Thursday, December 06, 2012 10:38 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] GPSDO Alternatives

As a lurker, I just want to chime in and say that I for one would love
to see an open-source GPSDO implementation. There are quite a few open
hardware designs out there, but as Bob suggests, all the interesting
bits are tied up in the closed-source software they run. And most of
them are no longer maintained, meaning it's getting hard to find parts.

I've thought on designing a hardware platform to support a GPSDO as
well, but don't have the time-nut or control theory skills (or
equipment) necessary to make the software any good. My hope at the time
was that a build it and they will come approach would solve those
problems, but I haven't had time to make that gamble.

As far as uP choice, Arduino's only saving grace is the pool of existing
'developers' in the amateur community for it - but that's perhaps a big
deal here. It's expensive, doesn't include debug hardware, and is slow
with not many peripherals. I'd second the STM32 ARM Cortex platform, or
suggest MSP430 if you want to stay cheap and slow.


On 2012-12-06 1:28 AM, Chris Albertson wrote:
> On Wed, Dec 5, 2012 at 2:50 PM, <SAIDJACK at aol.com> wrote:
>> If there is one thing I learned, it is that one is never finished
>>  the software. That is why we are time-nuts I guess.
> This is the reason I suggested using the Arduino.  It is so easy to
> that MANY people will be able to contribute.  That is my goal, a GPSDO
> can be a "living project" that is not dependent on one or a few experts.
> I'd like to see a budget of well under $100, again so that more people can
> contribute and experiment.
> A design that can evolve will have just about any performance people want.
>  So don't worry about if it is 1E-12 or 1E-15.  Just make it transparent
> and easy to understand and modify.

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