The various GPS pucks are made from a limited number of GPS modules. The SirfStar III (3) has been the standard for several years now and works very well; it is inside the BU-353 among others. The SirfStar IV (4) was designed for very low power
usage inside mobile devices like cell phones but is also found in some pucks and does not work
as well. These modules output NMEA
sentences on RS-422 serial
interfaces. For pucks that have USB interfaces there is an RS-422 to USB bridge chip added, usually a Prolific brand. For any computer, Mac included, it is only necessary to have the driver for the bridge chip. Depending on the version of OS X you may have to download the driver from Prolific, or it may be already installed. No big deal. The NMEA
sentences are standard and are understood by all nav programs and GPSD.
The u-blox 6 is considered better than the SirfStar III, but is a little harder to find (u-blox 7 is currently shipping
but I have no info.). The pucks are smaller as there is no need for the bridge chip - the module has USB output as well as RS-422. The output is clocked at 9600 instead of the common 4800. If you are out shopping
then one of these would be (marginally) the best choice. I have used one of these, as well as the BU-353, on my Mac for OpenCPN
with no problem.
I also have a couple of MR-350 mini-mushrooms; I use their NMEA output for input to DSC
radios and a Furuno chartplotter
. Needless to say they are much cheaper than the "marine" ones and work at least as well.
Garmins are another matter entirely: they have their own communications
protocol. Apparently OpenCPN
supports them, as does GPSD, but I see no reason to go with them.
BTW I doubt the magnet on the bottom of the puck
is strong enough to mess up the hard drive, although it is always wise to keep magnets away. If you want a really strong magnet then take apart an old hard drive: the internal magnet used to move the head
is the strongest you will likely encounter. Do be careful though: it can be really painful to get pinched between one and the fridge...
For setting up the GPS with the Mac choose the input as "/dev/cu.usbserial" and 4800 baud (or 9600 for u-blox 6). You will have to select the input sentences as well; to do this it is easiest to download a program "GPSutility" from the folks who make MacENC in order to see what the GPS is sending out.