Junction box, sensors, and ports

[newbie-]

I have a junction box for an AIS unit and I'm trying to understand these connections. Typically, I'd expect for data such as GNSS, heading, speed, and etc to exist on a NMEA 0813 or NMEA 2000 bus.

In that case, the bus connections don't mater right? For either 0813 or 2000. All the data is available in digital from anywhere on the bus.

On the junction box the inputs are labeled with expected sensors. How can that work? You don't isolate data on NMEA and "send it" somewhere with a cable, right?

OR does it really not mater at all what sensor is connected to which input on the junction box?

[Be Free]

It would help to know more about the AIS unit, but the diagram looks like a way to aggregate a number of serial (NMEA 0183) signals into a proprietary cable connecting the box to the AIS unit.


If the AIS can "talk" NMEA 2000 and you have all of the data on that bus already then this box may be optional.

[newbie-]

Originally Posted by Be Free

It would help to know more about the AIS unit, but the diagram looks like a way to aggregate a number of serial (NMEA 0183) signals into a proprietary cable connecting the box to the AIS unit.


If the AIS can "talk" NMEA 2000 and you have all of the data on that bus already then this box may be optional.

My guess is they just wanted to reduce the number of cables going in to the back of the main AIS unit so they added a junction box.

It's the em-trak A100 AIS:
https://em-trak.com/wp-content/uploa...-manual-EN.pdf

Unfortunately, no NMEA 2000 support. I'm a little bummed to spend hundreds of $ on new electronics without NMEA 2000. But seems like the closest alternative option for a class A ais is pushing thousands of $.

The plan is to use a NMEA 0183/2000 gateway to integrate and OpenCPN as the interface.

[Dsanduril]

Originally Posted by newbie-

I have a junction box for an AIS unit and I'm trying to understand these connections. Typically, I'd expect for data such as GNSS, heading, speed, and etc to exist on a NMEA 0813 or NMEA 2000 bus.

In that case, the bus connections don't mater right? For either 0813 or 2000. All the data is available in digital from anywhere on the bus.
...

NMEA 2000 is a bus system and what you say is true. NMEA 0183 is not a bus system. There can only be one talker on an NMEA 0183 network because there is no method of telling one device to shut up and let another one speak. Technically there is also only one listener, although since there is no response required you can have multiple listeners within the electrical limits of the serial signal.

If your junction box is built around NMEA 0183 then it has a bunch of listener ports for single devices, and then it aggregates all that data and sends it all back out over one or more talker ports. The box is, in effect, a multiplexer.

[Edit] Note that per the manual you posted the junction box is not a general purpose multiplexer, it only accepts DTM, GBS, GGA, GLL, GNS, HDT, RMC, ROT, THS, VBW, VTG, sentences on the input ports [/Edit]

[newbie-]

Originally Posted by Dsanduril

If your junction box is built around NMEA 0183 then it has a bunch of listener ports for single devices, and then it aggregates all that data and sends it all back out over one or more talker ports. The box is, in effect, a multiplexer.

So it sounds like it doesn't mater what device is connected huh? Since the sensors are only talking in this case.

The gateway I'm planning to use is the QK-A032-AIS-NMEA 2000/0183 Bi-directional:
https://www.quark-elec.com/product/q...ional-gateway/

So:
- NMEA 0183 output from the QK-A032 will connect to the sensor inputs on the A100 junction box.
- NMEA 0183 plotter output from the A100 AIS will connect to the QK-A032
- QK-A032 by USB to the PC

[newbie-]

Originally Posted by Dsanduril

[Edit] Note that per the manual you posted the junction box is not a general purpose multiplexer, it only accepts DTM, GBS, GGA, GLL, GNS, HDT, RMC, ROT, THS, VBW, VTG, sentences on the input ports [/Edit]

Ah. Hm. So I suppose that means my plan above won't do the trick.

[Scott Berg]

I have the same one; GREAT Unit (Class A), NMEA 0183 only but that's fine. The junction box is overkill for most yacht installs but it's required; it isn't a general purpose MUX but a dedicated, commercial grade, AIS only one.

[newbie-]

I reached out to quark-elec and they confirmed the QK-A034-B was what I needed.

- The AIS SEN1 (Junction box sensor 1) will connect to the QK-A034 0813 OUT
- The AIS EXT_DISP_OUT (Junction box AIS plotter OUT) will connect to the QK-A034 0813 INPUT

- The PC will connect to QK-A034 USB. And OpenCPN will communicate bidirectional with the AIS.
- The AIS will have N2K backbone data.

OpenCPN will be set to route 0813 data back OUT to the QK-A034 USB

It's a bit complex. But that *should* give me AIS targets on my plotter(s) and the AIS will get all the N2K and 0813 data on the network... Everyone should be happy.

If I'm lucky, the AIS will also automatically get and update the route info based on OpenCPN destination.