[time-nuts] [Solved] Looking for multiple PPS timestamp logging

Kevin Rosenberg kevin at rosenberg.net
Wed Oct 5 16:13:52 EDT 2011


Hi Didier,

Thanks for the idea. I haven't done any 8051 programming, but the price is great and you
list other advantages on your web site. I appreciate the recommendation.

Kevin

> A cheap way to measure temperature that will also be a good learning exercise would be to use a Silabs Toolstick. Most of their chips have a built in temperature sensor and a demo ADC program that spits out the temperature over the serial port emulated USB interface.
> 
> The toolsticks are all about $10 and you need a Base Adapter that is $15 I believe. The tools are free (demo, size limited Keil compiler, or the free unlimited SDCC)
> 
> More info on my web site in the Wiki
> 
> http://www.ko4bb.com
> 
> Alternately, you can buy a USB temperature sensor on eBay for about $10 I believe, but you won't learn much by using it...
> 
> Didier KO4BB
> 
> Sent from my BlackBerry Wireless thingy while I do other things...
> 
> -----Original Message-----
> From: Kevin Rosenberg <kevin at rosenberg.net>
> Sender: time-nuts-bounces at febo.com
> Date: Tue, 4 Oct 2011 09:03:56 
> To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
> Reply-To: Discussion of precise time and frequency measurement
> 	<time-nuts at febo.com>
> Subject: Re: [time-nuts] [Solved] Looking for multiple PPS timestamp logging
> 
> On Oct 4, 2011, at 4:36 AM, Hal Murray wrote:
>> In California, the diurnal temperature swings are big enough to be useful. :)
> 
> Here in New Mexico as well, useful or ruinous depending upon your application.
> Hence, I believe, your smiley face above ;)
> 
>> The swing would be much bigger outside, especially with an open sky.
> 
> We thought about an outdoor light and temperature sensor when my son
> considered measuring the stability of the PPS signal from a NetClock/2
> WWVB receiver. But, we'll be measuring the temperature near the indoor XO.
> 
>> I was thinking of keeping track of when you expected each pulse to arrive 
>> next and sleeping until a little before you expected the soonest one.  
>> (Adjust "a little" by trial and error.)
> 
> Sure, and the solution becomes more interesting the more pulse lines that
> are being polled.
> 
>> I agree that Tom's picPET will be a fine way to do it.  I was just playing 
>> with how to do it with the parallel port.
> 
> I lot of fine ideas come from thought experiments.
> 
>> It's still an interesting question of how accurate you need to measure the 
>> time.  That's probably a good one to work through with your son on the back 
>> of an envelope.
> 
> I think so, too. So, my son will be learning more about stability, Allan
> deviations, modified Allan deviations (which should be more useful for 
> the number of averaging points over a month), and improving his exponent
> skills.
> 
> Another statistic he'll be learning is the Pearson correlation coefficient
> to compare temperature (probably in Kelvin) to the XO frequency. The more
> precisely those are measured, the more likely the Pearson will reflect the
> true correlation.
> 
>> How are you measuring temperature?
> 
> Good question, because we haven't completely solved that. We'll be using
> a LM35CAH mounted next to the 32768 crystal and measuring the
> voltage once a second.
> 
> What I haven't decided is whether to have my son use the 34401A and GPIB
> polling via a Prologix adapter versus a simple MCU firmware using a 2.5V
> reference voltage and a 10-12 bit ADC and outputs the ADC result either
> once a second, or in response to a pulse (probably from the PPS of the XO).
> The first has merits of accuracy and simplicity, but I prefer he use
> more affordable devices than the 34401A in his experiment to even his 
> project compared with other students. The latter has the advantage of 
> price, but the disadvantage of me writing the firmware (though, the 
> firmware is almost trivial). But again, I'd like him to be as 
> independent as possible.
> 
> So, if you know of any simple ADC to UART firmwares available, that'd
> be great so he can just reference someone else's code. The picPET
> is a perfect device at the perfect time. But, we can't rely on tvb
> to come up with a 'picADC' at a similarly serendipitous time.
> 
> Kevin
> 
> 
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