T&T: Splitting the Signal of a USB GPS

[Peter Bennett]

While it is true that a GPS receiver is "just a talker", the USB
protocol requires the master (the computer) to ask the slave (GPS,
keyboard, mouse, whatever) if it has any data, and to send that data.

Cutting up two cables so you could try having two computers work with
one GPS would be an unnecessary sacrifice of two cables.

Since the USB protocol is completely unlike the normal RS-232 serial
protocol, I suspect that the GPS receiver you mention below must have
had both USB and NMEA serial interfaces.

Thursday, February 26, 2009, 8:43:06 AM, Michael wrote:

M> You may be right but the hockey puck type of gps is just a talker and 
M> usually has no provision for inputing data from the cpu.  I think it 
M> would be worth a try if you had a couple extra cables.  I once got a gps
M> to work with a computer by manually connecting the signal leads from a
M> usb gps to the appropriate inputs in a serial cable.  It's not rocket 
M> science... oh, wait, it is.  :-)

M> Mike

M> Peter Bennett wrote:
>> Wednesday, February 25, 2009, 8:50:09 PM, Michael wrote:
>>
>> M> If you are brave (or foolhardy) and good with a soldering iron you can
>> M> make a Y cable.  Most usb cables have a white, green, red, and black 
>> M> wire.  The better ones will have a separate shield.  The white wire and
>> M> the green wire are signal the red is +5 volts and the black is ground.
>> M> Cut one cable and attach the whites together and the greens together.
>> M> Don't connect the reds but the black and/or shield can also be 
>> M> connected.  You should have the white and green wires from the gps going
>> M> to each computer, only one computer should be feeding +5 volts to the 
>> M> gps and the grounds can be hooked together though the black wires.
>>
>> I don't believe this will work. USB is a complex master/slave
>> communications protocol, with the computer being a master, and
>> everything else being a slave.  Your suggested Y-cord will have two
>> masters trying to communicate with the same slave.  It is highly
>> unlikely that either computer will communicate successfully with the
>> GPS, and the arrangement may mess up other USB communications on both
>> computers.




-- 
Peter Bennett, VE7CEI    Vancouver, B.C., Canada
Ennos 31 "Honeycomb"
GPS and NMEA info: http://vancouver-webpages.com/peter 
Vancouver Power Squadron: http://vancouver.powersquadron.ca