Is the OPTO-4 a direct replacement for the PC-OPTO-3?

Yes, the OPTO-4 is a direct replacement for the PC-OPTO-3. The functionality is the same, please see the data sheet for the physical differences on the OPTO-4 downloads page.

For more information on NMEA 0183 and how it works, please download our free guide to NMEA 0183 networking here: https://actisense.com/everything-to-know-about-nmea-0183-guide/
For more information on NMEA 2000 and how it works, please download our free guide to NMEA 2000 networking here: https://actisense.com/complete-guide-to-building-an-nmea-2000-network/