| Hi!
Just a quick note to add that an easy way to kill GPS a few feet away is to use an USB3 to SATA adapter. Wipes out my GPS reception every time I test a cheap one!
On a side note, my Uputronics module from airspy.us works nicely sitting on a Pi4 with a separate antenna a few feet away indoors.
Martin VE2MRX On Dec 14, 2021, at 08:36, Don Rolph <don.rolph@gmail.com> wrote:
Nice module, but I really need a USB connection for the present design. However, there seem to be a number of GPS modules on eBay at your link, Since the GPS unit's only requirements are that it be within the Pi Zero form factor AND connect with USB, substitutes are straightforward and I will poke some more. Thanks!
What is the negative downside of the Adafruit GPS modules based on the MT3333 chipset compared to say the U-blox chip sets?
It is possible the foil is acting as a ground plane increasing sensitivity. However that does not then explain why it is highly sensitive in the open away from the assembly, and apparently desensed near the assembly.
But if you are correct and it is acting as a ground plane, then that is a two way street and it is also acting as a ground plane for the modules below and directing their noise away from the module. Either way: it does not work without it and works with it. I know for a fact from other testing that all the modules are very noisy electrically, the system is sensitive to this noise, and managing electrical noise in the configuration is critical for the design.
I have no plans to buy SIRF chips in the future: the present standard solution uses them and this is a replacement for the present design. And since the SIRF chip for this application is the default standard, if the new system is as good as or better than the SIRF chip, we are good to go. It is the present vendor has to deal with the shortage of SIRF chips.
Thanks for your comments and assistance!
And any further leads/comments on alternate chip sets for GPS modules within the PI Zero form factor AND using USB would be much appreciated!
On Mon, Dec 13, 2021 at 9:16 PM Gary E. Miller < gem@rellim.com> wrote: Yo Don!
On Mon, 13 Dec 2021 21:03:24 -0500
Don Rolph <don.rolph@gmail.com> wrote:
> One can certainly do better and cheaper for GPS units, but for a GPS
> unit at a reasonable price within the PI Zero form factor, this
> appeared to be among the cheapest.
Your choice, cheap, or good. Uputronics and sparkfun and not much more
expensive, and way better. Or for cheaper than the Adafruit you can get
a better GPS on a break board.
For $25, you can get a u-blox M8030 like this:
https://www.ebay.com/itm/284328934112?hash=item4233533ae0%3Ag%3AUd0AAOSwhKpgwzIe&LH_BIN=1
Smaller, cheaper, better. Should be half that price, but, inflation
and supply chain issues...
> This is part of a stack of boards based on the PI Zero W or PI Zero 2
> W. The emissions from the PI Zero, USB WIFI chip, and USB hub
> preclude the GPS board from making a fix.
Many have done that, you are the first to report any issue.
> This is easily
> demonstrated by experiment. Having the GPS board far removed from the
> stack results in a rapid fix. Placing the GPS board at the top of the
> stack results in never getting a fix. Introducing the aluminum foil
> shield between the GPS board and the rest of the stack now allows fix
> to be achieved. Making the foil larger and slightly curved causes the
> GPS to achieve fix in typically seconds.
Sounds more like you are adding a ground plane that increases the
sensitivity of the MT333x. If it works for you, then great.
> If I want to fit within the PI Zero form factor, the foil shield must
> be smaller and hence has less impact on the speed of achieving a fix.
And no chance for an external antenna?
> And for this version of the project I have to fit in app[oxiately
> the PI Zero W form factor. Other versions of this project typically
> use a GPS puck unit which does not have this problem.
Of course pucks have their own issues.
> Actually I can't ignore SIRF: for the application the standard
> equipment presently used uses the SirF chip: if I exceed SIRF chip
> performance then this is better than the present solution.
Good luck buying SiRF chips in the future. Easy to beat something you
can't buy.
RGDS
GARY
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gem@rellim.com Tel:+1 541 382 8588
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