Rats Nest - Indoor Boaty Stuff.

 I had originally intended to work on the window of the boat the weekend just gone. In fact I booked the following Monday and Tuesday off. But as usual events conspired against me....

So the first problem was that I had my second Covid jab on the Previous Friday which knocked me out on Saturday. Plus the booking for my car I had on Friday was also moved to the Saturday. So Neptune or the Almighty obviously didn't want me to work on the boat on Saturday. 

Sunday dawned miserable and wet. So no window-replacing action that day either. Okay, I get the hint.

So,, the plan was to indoorsy stuff for the boat instead. The electronics need to be rigged out and sorted so they can talk to each other. Yes, I delved into the intricacies of NMEA 0183. Considering I've had all the bits on hand for nearly a year, it's about time I did something with it all!

So, lets explain what I was about to do. I wanted to expand the existing basic setup to incorporate my freebie chartplotter along with my freebie GPS repeater and as a bonus add the Quark AIS unit with WiFi capability, which should pass AIS data to the chartplotter and also get NMEA info including AIS data on the Navionics app on my phone. A bit of an upgrade!

So lets explore each element in turn.

First is my old faithful Midland DSC VHF transceiver. This is the one I changed the MMSI on years ago.

Currently it's connected to a small GPS receiver to provide position information to the DSC side of things. It receives NMEA data at 4800 baud. 

Second is My Freebie Garmin Chartplotter. It receives GPS directly with an internal antenna. It also has the ability to input and output NMEA 0183 data on two ports at either 4800 or 38400 baud (fast or slow). 

So navigation data can be sent out from the chartplotter to other devices and it can receive other data from other devices.

Third is the NASA Clipper GPS repeater. It receives NMEA 0183 navigation data at 4800 baud. 

The Fourth and final unit is the Quark QK-A024 AIS receiver and BNMEA WiFi bridge. This unit receives AIS data and transmits it to the NMEA network. It also receives NMEA data from the network. It broadcasts the combined input and output NMEA data out via WiFi.  It receives and transmits data from the NMEA network at the faster 38400 baud. It does not support 4800 baud.

There are a couple of downsides to the Quark unit.  The first is that it only runs off a USB connection. You have to buy a unit to drop 12v down to the 5v the unit needs for it's USB connection. The second is it adheres to a "proper" implementation of the NMEA 0183 standard, which the other NMEA devices I have don't do. More about that as we go on. 

So, the first issue was the VHF wasn't talking to it's GPS receiver. I thought I'd keep that as a backup just in case, so I needed it to work to confirm the NMEA input worked before it started to get complicated.

Here's a little taste of how complicated it got:

Not quite Superyacht levels of tidiness and professionalism, but I'm the Skint Sailor and no-one's paying me so I don't care. 

So a bit of prodding with the multimeter showed a break in the power supply from the VHF to the GPS receiver. A bit of soldering later and the two were talking together. NMEA input on the VHF confirmed. Now it should receive NMEA data from another device.

So, fire up the chartplotter. Having two NMEA ports, this becomes the hub of the network. I set the first port as high speed (38400) and the second port to slow (4800 baud). The VHF only has a single wire input for NMEA. The second wire is connected to earth. So the 4800 baud TX output of the chartplotter was connected to the 4800 baud RX input of the VHF. The VHF then displayed NMEA data from the chartplotter. That was relatively easy, the only hard bit was soldering the wire to a new plug to connect to the back of the VHF.

Now the GPS repeater. That also just requires a single wire input, so it was connected to the same output wire from the chartplotter wire as the VHF. Another success! Position data appeared on the LCD screen. I'm sure course data will be displayed once the chartplotter has course info to broadcast on the network.

Next the biggie (although physically it's the smallest unit): the Quark AIS/WiFi unit. Now there are a few issues. The first is that the Garmin uses a different spec of NMEA interface to the Quark unit. The Quark uses a proper implementation of the physical or electrical properties of the standard requiring 4 wires to transmit and receive, whereas the Garmin unit only uses 2 to do the same thing. 

Being technical the Quark unit uses a differential or balanced interface, so you have IN +ve and IN -ve for the input and OUT +ve and OUT-ve for the output. The Garmin unit just has one TX wire for the output and one RX wire for the input. The other two wires are effectively connected to earth.

The difference requires an interface of some sort. Enter the QUARK QK-AS03 Protocol interface. 

The interface requires a 12v supply (easy). It has two input wires TX/RX. So the output (TX) wire of the chartplotter goes to the RX input of the interface. Similarly the input (RX) wire of the chartplotter goes to the TX output of the interface unit.

Now the four wires on the other side of the interface. The OUT +ve and -ve wires of the interface go to the IN -ve and +ve wires on the AIS unit. 

And obviously the IN -ve and +ve wire on the interface go to the OUT -ve and +ve wires on the AIS unit. 

The bad new is there is no display on the unit, so how do you know it's receiving and transmitting data? If you're close to the sea, then you hook up an AIS antenna to the unit and it should start pumping AIS data onto the NMEA network. The chartplotter, if it's set up for it should start displaying AIS targets on it's screen.

I'm situated a couple of miles away from the sea in a built up area. The Quark unit is only set up to receive very local AIS transmissions. It's pretty deaf as receivers go I assume deliberately because you're normally only interested in AIS signals within a mile or two.

The way I checked the functionality was over the wifi. The Quark unit acts like a WiFi router you have at home. You log onto it (no internet available). If you already have a WiFi router on board, you can change the setup to suit. 

Once logged onto the router, to see the raw NMEA data I use an app on the phone called NavMonitor. You tell the app the Quark unit's IP details (Host 192.168.1.100 Port 2000 and TCP protocol). You should then be able to select the log option and see NMEA data scrolling up the screen. Which, thankfully I did. 

So finally all the units were talking to each other. Success! All that was need was to start tidying the wiring a bit and in the case of the Quark WiFi unit, devise a way of powering it from 12v instead of USB 5v.

That was another days job.

The above is an over-simplification of all the steps. There was a bit of head scratching, lots of instruction reading and a few notes written out once I'd got things working. All told it was a couple of days work to get everything set up, solder up plugs where necessary and tinker until it all worked. 

Then I left it for a day to see if it could all interact reliably and repeatedly with a few switches off and losses of power to check how robust it all was. It seems it's all pretty solid - on the bench/conservatory table at least!

 So, that was most of my weekend, including Fathers day. Happily tinkering.

The next step is doing it all again whilst installing it all on the boat.....