[time-nuts] Thunderbolt Controllers

Neville Michie namichie at gmail.com
Mon Jul 7 05:42:12 EDT 2008


My pendulum produces pulses at a rate of one per second.
That signal clocks a latch that samples the less significant bits of  
my reference oscillator  (100kHz or 1MHz)
in a counter.
The latched values drive a 12 bit D-A converter (a R - 2R chain).
So I have a phase signal updated every second, and which resolves 10  
or 100 microseconds.
The data logger samples this every 10 seconds or so and so logs a  
graph of drifting phase.
The data from the logger can then be used in a spread sheet to  
analyse periodicity
of fluctuations and correlation to barometric pressure and temperature.
When barometric pressure and temperature are successfully eliminated  
by compensating
the pendulum, I hope to only have planetary resonances, gravity tides
and noise disturbing my clock.
Currently I have a 1MHz OCXO driving the system, but it drifts  
significantly.
This is a home brew oven, running at about 40*C, consuming about  
250mW, quite easy to
back up with a 12V battery.
The HOBO data logger has 4 inputs of 0 - 2.5 volts and 12 bit  
resolution, and it runs
for 4 years on a lithium cell.
It takes a lot more power to run a computer, and then you have to  
reboot after each power
interruption, and so I have not found it worth while to get a machine  
just for the project.

But the overall check of the system is to compare clock time with UTS  
once in a while
to cover the chance of slipped seconds. At the present time I use WWV  
when I can find it,
but what I would really like is a clock showing UTS in a form that  
can be compared to a clock.
That means one second audible pips and a marker on the minute. Just  
seeing numbers
rolling over on a computer is not good enough to check the timing of  
the second hand of
the clock. You need ear - eye coordinated signals. With WWV I can  
compare to 1/20th of a second.

Although I have programmed systems in a variety of languages in my  
working life, the only
languages that have stuck are Fortran and Basic. All the rest are  
forgotten after a year or two.
I do not wish to start again to learn a new system just for one task,  
and it is obvious that there
are so many micros abroad and none of them is going to be universally  
useful for future tasks.

cheers, Neville Michie


On 07/07/2008, at 6:01 PM, Hal Murray wrote:

>
>> The GPS may drop out, so a disciplined oscillator is in order, but
>> how can you get the GPS signals parsed to identify say minute markers
>> without running a computer?
>
> There are lots of 8 bit micros that are smart enough to parse the  
> stuff from
> a TBolt and wiggle a few pins.  You have to be happy writing that  
> sort of
> software.
>
>
>
>> With a small 4 channel data logger I can then record a clock for a
>> year and its relationship to UTC, temperature and barometric  
>> pressure.
>> I would only need a battery backup power supply for the TBolt.
>
> What are you going to record?  How often?  What triggers a recording?
>
> If you log things with a PC, then it's pretty simple to make your  
> PC track
> UTC so all you have to do is add a time stamp to each record.
>
> Or if your data logger has time but that time isn't good enough,  
> you could
> make the PC wiggle a pin on the printer port occasionally and make  
> that
> trigger a recording on the data logger.  You would either do it at  
> known
> times (say top of the hour), or get the PC to record when it does  
> it so you
> can sort things out later on.
>
>
>
> -- 
> These are my opinions, not necessarily my employer's.  I hate spam.
>
>
>
>
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