[aprssig] USB GPS for tracker

Scott Miller scott at opentrac.org
Tue Jan 28 12:17:19 EST 2020

I wrote an article on this years ago, but I'm too lazy to go dig it up now.

The problem with generic USB-to-serial conversion is that there's no 
single standard for how a USB GPS receiver might communicate with the 
host.  The USB standard provides a few types of endpoints (bulk, 
isochronous, etc) and the device can use those in any combination. The 
vendor's driver handles all of the interpretation on the host side.

*IF* the device happens to comply with an established class 
specification, then there will be a standard way of interpreting the 
data.  And maybe there's a class for it now, but there wasn't 
originally.  A device might create multiple endpoints, with one being 
NMEA data and others reserved for configuration or diagnostic info, or 
some secondary function.  The enumeration information returned by the 
device will tell the host which endpoints are bundled together and 
belong to what interfaces, but not what any of it means, aside from 
standard classes.

So yes, it's possible to make a USB host device that will act as a 
serial gateway.  It's far more complicated than going the other 
direction (adapting a serial device to USB) and would have to take into 
account many different GPS device to be practical.


On 1/27/2020 9:06 PM, Patrick wrote:
> you can't do that with USB because the whole point of USB is to make 
> the hardware cheap by making most of the heavy listing happen in 
> software, but the flip side is every device requires specific drivers, 
> which requires more than a postage stamp device, and if it could you'd 
> have to customize it for every usb device which would push you outside 
> of reasonable for this sort of project.  I mean you could do all this 
> with a pi zero, but if you're using a pi why not do the whole tracker 
> in software and get rid of the byonics thing  lol
> p
> On 1/27/2020 7:14 PM, jdubner at gmail.com wrote:
>> Patrick,
>> Thank you for your reply.  $12 certainly isn't "above my threshold of 
>> pain" but I was hoping there would be a postage stamp-size device 
>> that would accept USB and output serial similar to those available 
>> for Windows PCs.  Not so, I'm afraid so I will take your suggestion.  
>> Appreciate it and thanks again.
>> 73,
>> Joe, K7JD
>> Independence, OR  USA
>> Patrick wrote on 1/26/2020 21:07:
>>> It isn't typically easy and would vary depending on the GPS module 
>>> used in
>>> whatever usb device you have.  That said you can get rs232 GPS from
>>> AliExpress for ~ 12$ so it sorta is to the point that you would be 
>>> better
>>> off just spending the money for a working off the peg part.
>>> p
>>> On Sun., Jan. 26, 2020, 10:46 p.m. , <jdubner at gmail.com> wrote:
>>>> I have an old Byonics MicroTrak 300 APRS tracker and a couple of 
>>>> different
>>>> USB
>>>> GPS's.  Is there a cheap/fast/good way to adapt a USB GPS for this 
>>>> tracker
>>>> (and
>>>> set the baud rate to 4800)?
>>>> All that comes to mind is an Arduino project but that would bring on
>>>> additional
>>>> issues such as power requirements, RFI, size, and weight.
>>>> Thanks and 73,
>>>> Joe, K7JD
>>>> _______________________________________________
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