RTC Quartz datasheet available?
RTC Quartz datasheet available?
I try to understand a very odd behaviour of the RTC quartz of the PyBoard v1.1, and would like to have a look at the datasheet.
It would also help to know the frequency-temperature characteristic.
Posting of attachments (pictures) is in this forum not possible? It seems not to work for me...
Thank you
It would also help to know the frequency-temperature characteristic.
Posting of attachments (pictures) is in this forum not possible? It seems not to work for me...
Thank you
Ivo Gorny
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- Posts: 363
- Joined: Sun Apr 17, 2016 1:55 pm
Re: RTC Quartz datasheet available?
Most 32K quartz crystals have similar properties. You may get datasheet in some manufacturer.
Re: RTC Quartz datasheet available?
Not really. I tried a search using DigiKey, but even when narrowing down to 3.2*1.2mm 32KHz SMD, there are still dozens of hits left with sometimes very different special properties. The I tried the cheapest ones of those to see if the device marking can help, but nope.
Hence my question.
Hence my question.
Ivo Gorny
Re: RTC Quartz datasheet available?
What is the very odd behaviour?
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Re: RTC Quartz datasheet available?
You can post images when bb-code is on.
New users it defaults to off to prevent spam.
Make some more posts and bb-code will be switched on.
I think you may be able to make a post, edit it, manually switch on bb-code (a tick box near the submit button), try and add an image or code.
New users it defaults to off to prevent spam.
Make some more posts and bb-code will be switched on.
I think you may be able to make a post, edit it, manually switch on bb-code (a tick box near the submit button), try and add an image or code.
-
- Posts: 168
- Joined: Tue Nov 07, 2017 11:45 pm
Re: RTC Quartz datasheet available?
Just out of interest is it an official pyboard from the store
Or is it one of those half price ones on ebay coming out of china
Or is it one of those half price ones on ebay coming out of china
Re: RTC Quartz datasheet available?
My plan is, to write a code that fine-tunes the adjustment of the RTC depending on the temperature.
On my particular pyboard (bought from DigiKey), the correction value for ~25°C was -293, which i can determine using either of two different algorithms that use a GPS PPS signal as a reference. The algorithms are both giving the same results, and the clock is running pretty precise when adjusted using the correction value these algorithms provide.
I mounted a temperature sensor (DS18B20 in a TO92 housing) upside-down above the 32 kHz quartz, initially using a thermal compound.
The algorithms calculated the correction value now with -257 for ~25°C, and the clock was running precise with this value.
I first assumed the thermal compound may be (slightly) conductive, so I removed it using a toothbrush and methylated spirits, and the correction value was computed being back to the original -293.
The next test was done with another thermal compound (non-conductive), this time the correction value changed to -261.
Then I just removed the sensor, but left the compound on the quartz. The correction value stayed around -260.
Again I removed the compound, but this time the value did not came back to -293, it stayed at -289, even after deliberate use of toothbrush and alcohol. BTW, after cleaning, i dried the PCB with a hairdryer, to remove any potentially conductive remains of the alcohol.
For the next test I mounted the sensor without any compound, and the correction value is -286. And that is that, if the sensor is very close to the quartz or touching it, the value is -286, and moves to -289, when the sensor is moved away for more than ~5mm.
Robert thankfully posted a link to the app note which explains a lot of the sensitivity around the quartz (or crystal resonator), I assume, the stray capacitance is changing when I apply the thermal compound or mount the sensor. Doh'.
To me it seems that the quartz/crystal resonator is very sensitive towards stray capacitance, and that is a challenge - even just a shield mounted on top of the pyboard can alter the clock frequency...
Regarding the photos - This is post #24 in this forum, my first post was July last year. BB code is active since my third or forth post. And with a 43 kB file I get an error: "Sorry, the board attachment quota has been reached."
On my particular pyboard (bought from DigiKey), the correction value for ~25°C was -293, which i can determine using either of two different algorithms that use a GPS PPS signal as a reference. The algorithms are both giving the same results, and the clock is running pretty precise when adjusted using the correction value these algorithms provide.
I mounted a temperature sensor (DS18B20 in a TO92 housing) upside-down above the 32 kHz quartz, initially using a thermal compound.
The algorithms calculated the correction value now with -257 for ~25°C, and the clock was running precise with this value.
I first assumed the thermal compound may be (slightly) conductive, so I removed it using a toothbrush and methylated spirits, and the correction value was computed being back to the original -293.
The next test was done with another thermal compound (non-conductive), this time the correction value changed to -261.
Then I just removed the sensor, but left the compound on the quartz. The correction value stayed around -260.
Again I removed the compound, but this time the value did not came back to -293, it stayed at -289, even after deliberate use of toothbrush and alcohol. BTW, after cleaning, i dried the PCB with a hairdryer, to remove any potentially conductive remains of the alcohol.
For the next test I mounted the sensor without any compound, and the correction value is -286. And that is that, if the sensor is very close to the quartz or touching it, the value is -286, and moves to -289, when the sensor is moved away for more than ~5mm.
Robert thankfully posted a link to the app note which explains a lot of the sensitivity around the quartz (or crystal resonator), I assume, the stray capacitance is changing when I apply the thermal compound or mount the sensor. Doh'.
To me it seems that the quartz/crystal resonator is very sensitive towards stray capacitance, and that is a challenge - even just a shield mounted on top of the pyboard can alter the clock frequency...
Regarding the photos - This is post #24 in this forum, my first post was July last year. BB code is active since my third or forth post. And with a 43 kB file I get an error: "Sorry, the board attachment quota has been reached."
Ivo Gorny
Re: RTC Quartz datasheet available?
The 32 kHz crystal is sensitive to stray capacitance and also noise. The crystal requires 6pF load. Most of this (5pF) comes from stray capacitance - PCB and STM32. Only 1pF comes from the load capacitors. Any additional stray capacitance will affect frequency.
Noise is also an issue. If you place a temperature probe on the crystal and it is connected to a noise source, eg I2C or digital meter it will couple noise into the crystal. Note there is a ground guard ring around the crystal on the PCB to prevent the 12MHz clock and other signals coupling into the 32kHz.
I suggest you attach your temperature probe to an area of ground pour on the back of the PCB and this will give a reasonable approximation of the crystal temperature.
Noise is also an issue. If you place a temperature probe on the crystal and it is connected to a noise source, eg I2C or digital meter it will couple noise into the crystal. Note there is a ground guard ring around the crystal on the PCB to prevent the 12MHz clock and other signals coupling into the 32kHz.
I suggest you attach your temperature probe to an area of ground pour on the back of the PCB and this will give a reasonable approximation of the crystal temperature.