Temperature Controlled rasPi 3B

[Achim Gratz]

Gary E. Miller via devel writes:
> Cool.  Did you use ntpheat? 

No, I've simply extended the Perl script that logs all PPS timestamps
(this also ensures that all the measurements are aligned with the
loopstats).

>>  I still have to add an integral
>> term to the control loop in order to make the residual zero
>
> ntpheatusb already has a full PID controller.  Did you look at that?

No again, I avoid looking at Python as much as possible.

> If yu do so, could you send us patches for ntpheat?

See above.  It's really nothing spectactular, so I don't expect it will
be difficult to translate, however.

> I found that keeping the CPU chip temp stable was less important that\n
> keeping ambient stable.  The XTAL is on the other side of the PCB
> from the CPU.

I know.  I have described the exact setup in excruciationg detail to you
before, so I'm not going to repeat why the CPU temperature can be used
as a proxy for the ambient in that case.  Remember that this is about
getting the best possible performance out of the rasPi for exactly zero
cost above the rasPi and GPS itself.  That journey has come a lot
further than I first hoped, and I will keep it going for a while.

> I also found adding a fan to the box evened out the temps between
> PCB top and bottom better.

I have salvaged a few nice copper heatsinks from servers that were
thrown out at work that I will use later on for a better version of the
ovenized NTP server.  I already got some temp/humidity/pressure sensors
so I can check the actual temperatures and other environmental
influences.  It will most likely not make any difference for the
clients, so it's really just a game to see how far I can push this.

> Very nice.  What is the 'NTP Loop Offset'?  The Time offset?

Yes.

> How is the predicted frequency offset calculated?  Could that be patched
> into ntpviz?

I believe I've detailed the aging equations to you before.  Teasing out
the five model variables from the data requires a bit of care, but the
fit is easily done in gnuplot.


Regards,
Achim.
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