Garmin Serial Interfaces

Most current GPS units use a USB computer interface, however earlier units used a different serial interface called Serial Port, Com port, RS232 interface etc., if you need to connect your older unit to a computer there are a few challenges that need to be met as current computers don't have this 'Com port' any more


To start with there is the physical connection to the GPS, here are two commonly used by Garmin :-



Fig 1 - - - - - - - - - - - Fig 2

Type one (Fig 1) was used on the GPS38, GPS12, GPSMAP60 etc. and Type 2 (Fig 2) was used on the Etrex series, the corresponding plugs for these types are here :-



Fig 3 - - - - - - - - - - - Fig 4

Having purchased or fabricated your connector you will need to connect it to a serial Com port, these were common on older computers but you won't find one on a current computer, laptop etc., to get around this you can use a USB to Serial converter like the one shown here :-


Fig 5

To connect between your new connector and the USB to Serial converter you will need a cable, to make life easier you can purchase a connector with a cable, this should terminate in a Female 9 way 'D' connector that will mate with the USB to Serial converter, however if you only have the connector then you will need to purchase a 9 way 'D' type female connector and connect as follows :-

For Type 1 connector

Fig 1 top left = +5V to +8V supply (not connected)
Fig 1 top right = data in . . . . . . pin 3 of Female 'D' type
Fig 1 bottom left = data out . . . pin 2 of Female 'D' type
Fig 1 botton right = GND . . . . pin 5 of Female 'D' type

For Type 2 connector

Fig 2 first left = +5V supply (not connected)
Fig 2 second left = data in . . . . pin 3 of Female 'D' type
Fig 2 third left = data out . . . pin 2 of Female 'D' type
Fig 2 fourth left = GND . . . . pin 5 of Female 'D' type

Having connected your GPS to a USB interface you are almost there, however there may be other obstacles to overcome, for example if you wanted to use the 'Week Rollover fix' supplied by Garmin, this program allows you to choose a COM port from 1 to 4 but when the USB to Serial interface is connected to a current computer is very likely that the computer will allocate a COM port number outside this range e.g COM = 12, however the COM port allocation can be changed (See Week Rollover fix link)

NOTES
1) It is possible to purchase an all in 1 connector cable and serial to USB interface
2) When purcasing a Serial to USB interface, check to see what computer operating systems it works on, some older XP versions won't work on windows 8 / 10