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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.
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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-2 or NDC-3)
will fulfill most if not all requirements.
This product can combine, or
multiplex up to 4 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).
The NDC-2 also
features Inclusion Lists for each input port (to filter out unwanted NMEA
data).
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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.
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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.
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