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Cheapest way to get date/time from GPS

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SeanB:
GSM almost always likelty is running with UTC, as the signal has to go all over the planet, so all having time in UTC will work better, with the local mobile phone only getting, likely once the SIM provisions it, an offset to localise it for the carrier and region, allowing it to show local time and date. My phone at least does this, getting UTC time and offset from the tower, or you can manage it locally and set the offset manually. Likely going to be set on a tower to tower basis, especially in countries with lots of time zones, though I can bet it can be a hassle where you are sited at the border of the zones, and the phone wants to flip between zones.

tom66:

--- Quote from: shapirus on February 28, 2024, 02:38:58 pm ---Receiving time over GSM without even a SIM card (as, apparently, the time information is available in the broadcasted signal) is very interesting. Are there any existing modules that could be used for this?

I have an idea of taking an old nixie tube clock that is quite inaccurate to be used comfortably as it is, and replacing the internals with a decent crystal oscillator and RTC (+MCU) that would be periodically auto-adjusted, including initial setup, based on precise (and +/- 0.5 s is precise enough!) time acquired one way or another. This could be: a) NTP over WiFi; b) GPS; c) GSM (?).

WiFi requires initial setup (and reconfiguration when the connection settings change). GPS has poor indoors reception. GSM, if at all feasible, sounds like a perfect solution that would allow to build a clock with zero effort setup: just plug it in, wait for the time sync, done. The signal is available almost everywhere and can be received indoors, save for places like cellars etc. Well, maybe a button to set the time zone offset. And DST.

--- End quote ---

GSM is an interesting one.  I don't know enough about it to say for sure but it is possible the SIM card / eSIM tells the module which bands it is allowed to use?  If that information is not available it may well not be able to listen and/or transmit (legally, as some GSM bands in some countries are reserved for private functions, like military).

But that's just speculation on my part.

peter-h:

--- Quote ---AFAIK the time is in de mobile signal. No need for a sim card.
--- End quote ---

If that is so, it's amazing this is not widely used.


--- Quote ---but the posters tend to be coy about their details/motivations which is unfortunate.
--- End quote ---

Another reason for not posting much is that after a while it becomes very obvious that almost nobody will read a long initial post, especially if it contains source code :) So how much info to "feed in" is a matter of judgement...

switchabl:
New designs should almost certainly target 4G or 5G. GSM is not a viable option most markets any more: https://www.emnify.com/blog/global-2g-3g-phase-out

peter-h:
AFAIK, all "data" starts with a GSM connection, via a Hayes-like protocol, where you send ATDT*99# and you then get a TCP/IP connection and you connect your TCP/IP stack to the modem, and you get a "socket" interface. The data rate is automatically selected. I was doing that on the Siemens / Cinterion MC52/etc modems.

The above works the same way whether it is GPRS ("2G"), EDGE (basically double speed GPRS), 3G, HSPA (basically 3G but faster), 4G or 5G.

Voice and SMS still runs over GSM. AFAIK nobody runs voice or SMS over 4G etc. although the cellular system is free to do what it likes internally, and it probably runs everything over some IP protocol.

So, no GSM, no data. But in terms of coverage, you always have GSM. You never have say 4G coverage but no GSM coverage. What you do often have is GSM and no data, or GSM and only GPRS (which is too slow for "internet" use these days since even the HTTPS certificate exchange takes too long).

I did a search and could not find out what the towers transmit continuously.

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