JRC 1000

[Peegee]

I caught a bit about installing these last week, and yeah, I thought ."I know all that"..... However !!
Wiring up today I thought I would interface with my old but trusty Garmin 120XL. On the JRC I have NMEA + & - , on the GPS I have NMEA in & out . One of you geniuses must know how these relate.
I dont suppose it will wreck the set to get it reversed, but it would be nice to be right from the start.
Also, After checking with those that know at the Boat Show (well...so they claimed ) I have fitted the JRC display in the cockpit . On the last correspondence there was a very brief mention of preventing fogging if outside. any suggestions ?.

 

[alan]

The JRC will be a listener and therefore the + and - will be the input (a pair of wires). This needs to be connected to the GPS output (talker) which should also be a two wire connection. You need to identify the NMEA "out" + and - on the GPS; then connect the + of the JRC to the + of the GPS and the minus of the JRC to the minus of the GPS. If you mix up the + and - it will not do any damage but it wont work either.

 

[hightech]

Garmin use the 0 Volt line as the NMEA -ve.

So connect the Garmin NMEA out lead to the NMEA +ve of the JRC and a connection to the 0Volt lead of the Garmin to the -ve of the JRC. Then just check that the Garmin is set to outout NMEA0183 Don't cheat by looping the 0volt lead of the JRC to its NMEA -ve lead, you need to run it from unit to unit.

Geoff

 

[wooslehunter]

Here's a bit of technical stuff for anyone who's interested. The NMEA spec says that all pieces of equipment should be optically isolated from each other. So, the designers put something called an opto-isolator into the listener connections. This is just an LED packaged together with an opto-transistor. There's a physical gap between them inside the package and hence the two sides are isolated. You won't see anything light up if you look inside since the packages are designed to keep light out and therefore light is kept in as well and anyway it's ultra-violet light. The LED is connected to the input side and the transistor on the output side. When the LED is switched on, the phototranistor is illuminated and also switches on. Hence it's rather like a relay: you put a signal on the input and the output switch is closed. All this can happen very fast so data can be transmitted. The idea is that since the data is transmitted by the difference between two wires and the receiver is isolated, they can be powered from separate systems. If one equipment has a grounding fault and the power supply floats high, the other won't be damaged.

So what does this meen for yotties. All NMEA inputs should have two wires: + and -. These are connected to the LED. All NMEA outputs should also have two wires so the talker can drive the LED in the listener. If that's the case it's easy: connect the + wire on the GPS to the + wire on the listener and the same for the - wires. Job done. Don't get confused if the kit has in and out. That should be two pairs. i.e. four wires

BUT some talkers only have one wire out and one wire in. The ground wire is used as the - wire. Hence you don't really get true isolation but you do save a wire. This is the same as connecting a GPS to a DSC radio which is a really common question here.

Any questions? There will be a test next week & detentions for anyone who get less than 70%.

 

[Peegee]

Thank you one and all, that does make sense now !. But where do I put the key to wind it up !!.
Roll on Spring...
Peegee