[aprssig] USB GPS receiver

Stephen H. Smith wa8lmf2 at aol.com
Thu Oct 27 12:20:54 CDT 2005

web8ck at yahoo.com wrote:

> .
> I have a USB Holux GPS receiver (This one does not have the PS2 
> connector).  I purchased it for work.  I am no longer at that job and 
> now want to use it for APRS. 
> Is there a way to convert or adapt this receiver for use with a 
> tracker/tnc?  Holux sells this unit with a PS2 connector and adapters 
> can be used to do what I need.  I thought of making a pigtail with a 
> USB female to PS2 male/female (whichever is needed) then get/make the 
> adapter.  Will this work?  I have posed this question to Holux and 
> have not received an answer yet.

USB devices WILL ONLY WORK WITH A PC!   USB is a totally "PC-centric" 
protocol.  There is NO PRACTICAL WAY to make an external USB device work 
with a serial port on TNCs, TinyTraks, D700s, or anything else OTHER 
than a USB port on a PC.

USB devices have a master-slave relationship with a controller in the 
PC.  Without a PC "master" and complex multi-layer software driver 
infrastructure to initialize and assign them identities, USB devices are 
totally helpless. 

[ Standard USB connecting cables recognize this fact. The two different 
kinds of connectors are intended to prevent users from either trying to 
connect two masters to each other, or two slave devices to each 
other.    The wide, flat rectangular plug always goes toward a master.  
The smaller square plug with beveled corners always goes toward a slave 
device. ]

The common serial-to-USB adapter cable "dongles" are "slave" devices 
under control of the PC "master". They CANNOT function away  from a PC, 
and thus can't be used in reverse to convert other USB devices to serial.

Serial-to-USB converter cables are not just wire with different types of 
plugs on each end.  They are active devices with a microprocessor inside 
the DB9 housing doing the serial-USB translation.   Inside the PC, a 
special add-on software driver has to be installed that intercepts the 
USB data stream and converts it back to a simulated COM port.  Programs 
like UIview, Street Atlas, MapPoint, etc then use this simulated COM 
port.  (Some newer programs can now use the USB data directly although 
NO current APRS applications do.)

The USB GPS "mice" act exactly like a serial device connected to a 
serial-to-USB converter "dongle".   All GPS devices are serial 
internally and use a similar serial-to-USB conversion chip.   The only 
difference is that the chip is inside the GPS instead of inside the DB9 
connector of an external cable.    Exactly like the cables described 
above, a device-specific driver will be required on a PC to create a 
simulated COM port.  [In fact some USB GPS  devices use the identical 
chips as external converter cables, and as a result will work with the 
identical drivers.]

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