GPS data to Furuno 1715 Radar

[Roberto]

Hello,
I have a Furuno 1715 radar and would like to send gps data to it, so that the cursor position on the display shows its Lat/Long data. The radar can send NMEA data towards a plotter for example, but I do not need that.
The NMEA socket on the back is an unusual round 7-pin with all 7 pins on the outside and no central pin (all 7pin connectors on the internet show 6 peripheral pins + a central one), I could not find the appropriate female connector. Furuno sells a ready made cable (plug on one side, 7 coloured wires on the opposite) but it's >100euro, definitely too much for this "nice to have" feature.
The manual shows the diagram below for the plug wiring.
While searching the internet I found a (supposedly) Furuno message saying that NMEA data input to the radar is made through the Yellow (NMEA +) and Green (NMEA -) wires, numbered respectively 3 and 4 on the circuit diagram; the wire colours are related to their ready made cable.
I would like to attempt connecting the two NMEA out wires from my GPS to only two of the pins of the plug on the back of the radar; my questions
1. Is there a way to associate the pin numbers of the circuit diagram to the physical pins, those visible in the picture ? Which is number 3 and which is number 4? I only found the standard numbering for the other type of 7 pin (6+1 central one).
2. Or, is there a way to identify which pin is connected to which wire by using a multimeter (which is where my electronics knowledge ends ), I guess +12v and GND would be easy (pins 5,6,7), but the other wires?
3. The YLW and GRN are labeled respectively "RD2-H" and "RD2-C", is it normal to connect the GPS Nmea plus and minus to these two inputs, i.e. is it normal there is no connection to the Ground pin?
4. Could I make the physical connection for example with 2 single pin female Molex connectors? Or with what other means?
5. What happens if I take the NMEA out plus and minus from the GPS and try and connect it random to two pins, do I risk burning any circuitry?
Thanks in advance
r.

 

[andsarkit]

The pins will be numbered clockwise or anticlockwise from the key at the top. They will probably be numbered on the inside of the connector where the wires are soldered on. It might be worth using a torch and magnifying glass to see if there are any numbers visible on the outside.
Using a multimeter set to ohms you should be identify pin 6 and 7 which should be connected to the battery negative. You can do this with the instrument switched off so there is no chance of shorting the +12v pin 5 to pin 6. You can then count round to find 3 and 4.
MNEA implementation is often a bit loose with some manufacturers but I think Furuno will do it properly. The signal will make two wires high or low relative to each other which means that any interference that appears on both wires will not compromise the integrity of the signal. (simplified explanation).
Depending on the diameter of the pins you might be able to find a Molex crimp insert that is a reasonably secure fit. Use heatshrink around it for insulation.
If it doesn't work initially you need to check that the baud rates are set correctly from both ends. Also try to reverse the wires around as different manufacturers will call them + and - or high and low and there is often no consistent system of marking. This will not do any damage as an inverted signal will just be read as garbage.
There should be no need for a ground connection unless you want to connect an outer screen to pin 7.
The serial driver I/Cs used on equipment are reasonably electrically robust and are not easily damaged by wrong connection of 12V but it is still best to be careful. They are more likely to be damaged by electrostatic discharge if you are one of those people that keeps getting shocks when touching door handles.
Good luck and let us know how you get on.

 

[Roberto]

Thank you very much!
I'll try next time I am on the boat and report here.
Cheers, r.

 

[Roberto]

Just checked the pins, there is indeed a very tiny numbering on the inside of the connector (I needed my jeweler 10x eye lens to see them).
Looking at the photo above, pin 1 is the one NE, just on the left of the top notch, pin 2 is West, pin 3 SW, pin 4 South, and so on.
Pins 6 and 7 are located E and NE, they show zero Ohm so indeed shorted.
Now I'll try and find the molex connectors
regards r.

 

[Roberto]

Update
I eventually managed to do it
NMEA output from the GPS, + goes to pin in SW position, - goes to pin in S position. Several tries destroying a few different plugs to find two appropriate tiny connectors, eventually a couple of female pins from a sort of DIN made it.

Thank you very much again Andsarkit