Interfacing NMEA0183 to your computer

Lots of people want to know how to interface NMEA 0183 instruments to their laptops or other computers. One answer is to do it directly: NMEA data out -> RS232 data in, and NMEA data return -> RS232 ground. The signal is 4800 baud, no-parity, 1 stop bit.

But here's a better answer, courtesy of Bob Curtis (bc@gate.net): Here's a simple circuit to keep your instruments safe:

     a ----/\/\/\/\----+        +---+------/\/\/\/\------ +12v
             5k        |        |   |         5k
                      ---     |/    +-------------------- to RS-232 rcv.
                      / \     |
                      ---     |\
                       |        |
     b ----------------+        +------------------------ to RS-232 common
                                |
                                | <- might not need this connection
    gnd ------------------------+

You will have 100shown (recommended). Some systems may work more reliably with a common ground. The parts (2-5k resistors and a photo-optical isolator) will cost about $4 at any Radio Shack.