SwissMicros Calculator Forum

Walter wrote: ↑

Sun May 12, 2019 8:28 am

Bom dia Jose, y muito obrigado for pointing to your comprehensive investigation. I admit I've read it a year ago but didn't remember. BTW, please note you called the quartz a "high precision crystal" in your post of 2018-02-11 and didn't relativize this statement any later AFAICS.

Guten Morgen, professor Walter,

My bad calling it as "high precision".
I can't remember where i got that from, most probably from some optimistic datasheet.
I will have to search it again to do an update.

By the way, i was reading the Swissmicros adverts and the online user guide and i could not find references to a RTC feature. However the DM42 features date and time settings, so i agree with you that it should not exhibit several minutes time drift per year.

I am sure someone associated with Swissmicros will have a logical explanation for this.
Also i can not assume that all the DM42 machines are using the same type of crystal as seen in the picture that i used as reference.
Generalizations can be dangerous...

Jebem wrote: ↑

Sat May 11, 2019 9:03 pm

the worst case scenario for the reported clock issues should be around 6 minutes after 6 months.

Should... I could throw in the ring 38 minutes loss after 14 months.

Hans

Hans S. wrote: ↑

Sun May 12, 2019 2:01 pm

Jebem wrote: ↑

Sat May 11, 2019 9:03 pm

the worst case scenario for the reported clock issues should be around 6 minutes after 6 months.

Should... I could throw in the ring 38 minutes loss after 14 months.

Hmmh, one could build a more precise clock using two DM42's ...



... one fixed and the other acting as a pendulum.

O HELVETIA, VBI QVALITAS TVA?

Walter wrote: ↑

Sun May 12, 2019 2:40 pm

Hans S. wrote: ↑

Sun May 12, 2019 2:01 pm

Jebem wrote: ↑

Sat May 11, 2019 9:03 pm

the worst case scenario for the reported clock issues should be around 6 minutes after 6 months.

Should... I could throw in the ring 38 minutes loss after 14 months.

Hmmh, one could build a more precise clock using two DM42's ...



... one fixed and the other acting as a pendulum.

O HELVETIA, VBI QVALITAS TVA?

Then you would need to enlarge the reset hole to fit a winding key...
I have even designed a proper UI for it:

viewtopic.php?f=14&t=2181

Walter wrote: ↑

Sun May 12, 2019 2:40 pm

... one fixed and the other acting as a pendulum.

Old saying: The man with one watch knows what time it is. The man with two watches is never quite sure.

Hans S. wrote: ↑

Sun May 12, 2019 2:01 pm

Jebem wrote: ↑

Sat May 11, 2019 9:03 pm

the worst case scenario for the reported clock issues should be around 6 minutes after 6 months.

Should... I could throw in the ring 38 minutes loss after 14 months.

Hans

Clearly this would require investigation to find the roor cause(s).
The hardware oscillator must be stable and within the required time drift, before investigating issues in the firmware.

The good news is that we do not need to wait 1 month to check the clock drift:
Take a lab high impedance frequency meter and read the oscillator frequency. The reading should be 32768 Hz with ad many decimal zeros as possible. If it is outside the required tolerance (as expected):
1. Replace the crystal with a Seiko or Epson low drift crystal (10ppm or 5ppm) and check again.
2. The crystal MUST be loaded properly to tune the frequency by adjusting the load components. Use only temperature stable capacitors and resistors. A trimmer capacitor could be used during developing and testing stages. I don't know the exact oscillator diagram chosen by the manufacturer as i do not own a DM42 (not yet).

The bad news is that in order to troubleshoot these type of hardware issues we need lab grade equipment that i don't have access.
Maybe one of the members owning a DM42 have access to a university electronics lab and ask someone to take meadurements?

Any practical reason why accurate time is important on this calculator?

IMHO, it does not need to know the time or date. Calculations on time or date values, yes, but I'll happily look elsewhere for accurate measurements.

Am I missing something? Except that the original HP42S has it? BTW, how accurate was / is the original?

H2X wrote: ↑

Mon May 13, 2019 12:16 am

Any practical reason why accurate time is important on this calculator?

IMHO, it does not need to know the time or date. Calculations on time or date values, yes, but I'll happily look elsewhere for accurate measurements.

Am I missing something? Except that the original HP42S has it? BTW, how accurate was / is the original?

I agree with your sensible comments, and no, the HP-42S did not have any clock/date function at all. Because Free42 runs on platforms that all have built-in clocks, Thomas added the Date/Time features, modeled after the analogous functions in the 41CX (or 41C/CV with Time module).

All the original 41 versions (CX or module) included a crystal, were reasonably accurate, and also provided user functions to correct time drift over longer periods. That said, those commands were tedious and not well understood (though the manual was IMHO pretty clear) and many (most?) users simply set the time again manually when they noticed the time had drifted.

rprosperi wrote: ↑

Mon May 13, 2019 12:37 am

All the original 41 versions (CX or module) included a crystal, were reasonably accurate ...

What does this mean in numbers?

I certainly never bothered with CORRECT/SETAF/RCLAF on my HP-41CX, but those were also the days when I still used a mechanical wristwatch, so my standards of timepiece accuracy were not very high.

Of course nowadays, I rely on my smartphone to tell time, and it synchronizes with time servers on the Internet. The only clocks I still use that require manual adjustment are the one in my DM42 and the one in my car.

20 ppm is about a minute per month. That sounds about right, but in order to help inject some more accurate data points into this discussion, I synchronized my DM42 with time.gov yesterday; I'll check in a week to see how much it has drifted and report back. A week should be enough to get a good sense, should be several seconds of drift over that kind of time interval.