Why would I want or need an NMEA opto-isolator adapter cable?
Simply put, to protect your computer investment - if the serial communications port on a laptop is damaged, it is normally a very expensive repair that could require replacement of the entire motherboard. This cable allows easy, safe and low-cost connection of an NMEA 0183 system (or any other compatible RS422 / RS485 system) to a laptop or PC, by matching a standard RS232 D-type 9-pin serial port to an NMEA 0183 type marine bus link.
Potentially damaging voltage or current spikes can be present in the electrically noisy environment of the vessels wiring network - alternators, motors etc. can induce or conduct very large voltage and current spikes into the vessels power cables; computer ports (RS232, USB etc.) are designed to handle low voltage and low current signals only and are easily to damage in the marine environment.
This adapter cable needs no external power supply as the interface takes all its power from the computer port. Once the cable is wired to the NMEA 0183 network, and the connector plugged into the computer, the data will be available via its serial communications port.
The computer, radar or chart plotter will then be capable of reading any transmitted NMEA 0183 sentences, for display by any standard NMEA 0183 display software, such as a chart plotter program or the Actisense NMEA Multi-display program, and will also able to send NMEA 0183 sentences back to the attached instrument.
If however, you require more flexibility for a RS232 / computer source to add its own NMEA data to the NMEA network, the Actisense NMEA Multiplexer (NDC-4) will fulfill most if not all requirements.
This product can combine, or multiplex up to 5 NMEA 0183 instrument outputs together, and in addition, multiplex in the NMEA data from a computer via its dedicated RS232 port (standard computer serial port).
Can I use the NMEA opto-isolator for other non-NMEA uses?
Yes. The NMEA Opto-isolator adapter has been specifically designed to work as an isolator for the NMEA system. However, it can also be used in most systems that use the RS422 or RS485 (4-wire) connection protocols.
The Opto-isolated adapter cable utilises a full Galvanic Opto-isolated input circuit to protect the RS232 / PC's receiver and a TransZorb diode to protect the RS232 / PC's transmitter.
This adapter cable also converts the RS422 / RS485 (NMEA) voltage levels to RS232 (PC) voltage levels, and vice-versa.
As an example of alternative uses, by using two adapters at each end of a cable (back-to-back), the normal maximum RS232 cable length of 20 metres can be extended up to and beyond 100 metres. The longest 'cable extender' length currently acheived by a customer is 200 metres.
In the RS232 / PC receive direction, it provides complete isolation of expensive RS232 / computer hardware when connecting to an NMEA 0183 bus link that may have picked up potentially hazardous voltages around the electrically noisy environment of a boat.
In the RS232 / PC transmit direction, a TransZorb diode provides a high level of static spike protection, but does not offer the complete protection of an opto-isolator and so is only recommended for connection to equipment with Opto-isolated inputs.