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Cheapest way to get date/time from GPS

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peter-h:
I've looked at this topic from time to time over past 30 years...

You need to receive just 1 satellite. Experimentally, it is clear this works even with a really poor signal which is nowhere near getting a position fix.

But what is the minimum hardware, and does it exist?

For maybe $5 (in 10k+ volume) you can get a GPS module e.g. u-blox which will do this out of the box. But it is quite big, draws quite a lot of current (10s of mA), and exposes you to a short production life of a "fashionable" component.

It would be nice if one could use some cheap RF chip, with a short PCB track as the antenna, and with some cunning software extract just enough to get the UTC time.

The opinion I've got over the years, from apparent GPS experts, is that this is not possible.

nctnico:

--- Quote from: peter-h on February 26, 2024, 04:46:19 pm ---I've looked at this topic from time to time over past 30 years...

You need to receive just 1 satellite. Experimentally, it is clear this works even with a really poor signal which is nowhere near getting a position fix.

But what is the minimum hardware, and does it exist?

--- End quote ---
Something like a MAX2769 should get you going provided you can do the IQ demodulation and decoding in software. Likely there are similar chips from other vendors which are more price friendly.

jc101:
The newer U-Blox M10 chips draw just over 10ma during acquisition, dropping to 5ma once signal aquired.  Not the cheapest though, but easy to integrate.
No idea of the price for 10k+, but the UK distributer would no doubt give you a quote - https://alphamicro.net 

soldar:
For what purpose? Because if it is anything that needs to work indoors then it will not work.

peter-h:
I buy u-blox from Mouser etc - same price as any disti, below 1k or so :) But still pricey.

The MAX2769 is interesting but expensive. If it was say £1, that would be really handy for this job. As an interesting aside, the Marconi patent on fractional-N has expired, hence this...

You can get GPS indoors if there are any windows. Certainly will be a problem if deep in some bunker but most office/factory scenarios are workable.

And then there are scenarios where there is no signal but running a coax to an antenna elsewhere is entirely acceptable e.g. in GPS to NTP boxes which are used in specific scenarios where for security reasons an internet connection must not be made. I make a product which (among other features) does GPS to NTP and it works great. It uses a NEO-M9N module which draws some tens of mA (warm to touch).

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