Beginners guide to Nmea 2000, Nmea 0183, and bridging

Most of the new instruments for boats are now coming out with NMEA 2000 (National Marine Electronics Association) as the preferred method of connecting various devices on a boat. The NMEA 2000 transmits data through Controller Area Network (CAN bus). It simplifies the connection and shares information among different devices by using a single trunk cable. Compared with NMEA 0183 in “RS422” interface, NMEA 2000 has better transmission reliability and shares data easily in a network. 
Here's a good primer for constructing NMEA 2000 networks
And Power and Motor Yacht has an article worth reading; " A Breakdown of Protocol: How a Boats' System Converse"
 I'll attempt here to explain some of the data networks and how to connect various different types.

Typical Nmea 2000 Backbone.

The Nmea 2000 Backbone is pretty easy to set up as you can see from the diagram. All you need is the right parts/cables/terminators and follow some simple rules. Read the link above for the do's and don't's. Even hooking in a new device is relatively easy. More hooking up Legacy Equipment to this network later. But here is some tables that illustrate the differences between the old and new nmea standards.

Nmea 2000 verses Nmea 0183

Nmea 0183
Nmea 0183 and it's various versions is the older standard from NMEA. But it will be around for quite a bit longer.
NMEA 0183 is a low-cost, low-capacity, single-transmitter/multi-receiver network for
interconnecting marine electronic devices, also known as a “single talker/multiple
listener” interface. The NMEA 0183 Standard, along with RS-232, RS-422, etc., is often called “Asynchronous Serial” interfaces. This means that data is transmitted serially (bit-by-bit) on a single line. Furthermore, the transmission is asynchronous because no “clock” signal is transmitted with the data.

Single Talker, Multiple Listener

Multi Talker to Single Listener

There are multiple versions of the NMEA 0183 specification in use in the marine industry.  Prior to NMEA 0183 version 2.0, including NMEA 0180 and NMEA 0182, the hardware employed a single ended interface implemented with one signal wire and a common ground. Early versions of the NMEA 0183 Standard specified that “listeners” must be isolated from ship’s ground but allowed ”talkers” to be simple single-ended drivers (referenced to ground). Furthermore, the input impedance of a listener was specified to be greater than 500 ohms, and opto-isolation was recommended. Later versions of the Standard retained the opto-isolated listener recommendation, but revised the talker requirement to be RS-422 compliant. As a result, there exist some instruments (talkers) with single-ended outputs and others with RS-422 (differential) outputs.
All implementations from 2.0 and later employ a differential interface with two signal wires.

Due to the difference between the single ended and differential interfaces 
implemented, older versions of NMEA 0183 prior to 
version 2.0 cannot be connected to equipment supporting NMEA 0183 version 2.0 or higher without proper interface circuitry. Do not connect one of the signal wires of the differential interface to the common ground of the single ended interface!  
Single-ended drivers are perhaps the simplest to design. The desired state indicated by the presence or absence of a voltage above some threshold. For NMEA 0183 (ver. 1.5), a “one” was any voltage less than +0.5, while a ‘zero’ was any voltage greater than +4.0. Besides their design simplicity, single ended drivers need only one wire to transmit data. Since voltages are referenced to Ground, no signal return line is needed.
Interconnecting NMEA instruments can be a real hassle if one is not familiar with the different types of connections. The NMEA-0183 standard specifies the talker ports (outputs) and listener ports (inputs) to be differential. This means that the data is transported by means of voltage levels over two wires, separated from ground. Roughly, the voltage levels swing between 0 and 5 Volt, and both wires are in opposite phase. When one is at 5V, the other is 0V and vice versa
Some  manufacturer's though, would not adhere to the standard. It would have been perfect if you could simply connect the 'A' terminal on a talker to the 'A terminal of a listener and do the same with the 'B' terminal. So what came about were these "single ended" connections which complicated matters for the DYI person.

There are four types of connections possible with differential and single ended.
They are,

• Differential > Differential
• Single ended > Single ended
• Single ended > Differential
• Differential > Single ended

What distinguishes NMEA 0183, RS-232, and RS-422 from each other is their physical voltage and current interface levels. NMEA 0183 originally allowed “single-ended” drive, but was later updated to differential drive (RS-422).  RS-232 is a bipolar interface and RS-422 is differential drive. These are explained in more detail next.

RS232 data is bi-polar. +3 TO +12 volts indicates an "ON or 0-state (SPACE) condition" while A -3 to -12 volts indicates an "OFF" 1-state (MARK) condition. Modern computer equipment ignores the negative level and accepts a zero voltage level as the "OFF" state. In fact, the "ON" state may be achieved with lesser positive potential. This means circuits powered by 5 VDC are capable of driving RS232 circuits directly, however, the overall range that the RS232 signal may be transmitted/received may be dramatically reduced. RS-232 interfaces are somewhat sensitive to environmental noise (motors, ignition pulses, etc.) and are therefore usually limited to installations of tens of feet or less.

RS-422 is most commonly called “differential drive”. Two wires, A and B are used for this interface, but neither wire is grounded. A “zero” is produced by making A positive with respect to B and a “one” by making B positive with respect to A. It is therefore the direction of current flow rather than a voltage level that determines the logic state. It is important to note that neither RS-422 signal line (A and B) can be connected to Ground.


RS-232 interfaces are somewhat sensitive to environmental noise (motors, ignition pulses, etc.) and are therefore usually limited to installations of tens of feet or less.
RS422 standard that is widely used for the transmission of high speed serial data. Transmissions using RS-232 are limited in their speed and the length over which data can be transferred. Normally the maximum is 19.2 k baud and the distance 15 metres, although for slow transmission speeds longer lengths can sometimes be used.
It is very immune to external noise, and so can be used over greater distances (hundreds of feet).Under the latest version of NMEA 0183, all talkers are supposed to be RS-422. RS-422 is not strictly compatible with RS-232, but most RS-422 drivers will act like a single-ended driver if only one output line is used. In this way, the RS-422 “A” output can be used to drive either an RS-232 input directly. The “B” line is simply left unconnected.
Fortunately, both types of outputs will drive opto-isolated listeners. What is "optp-isolation"... Opto-isolators are actually quite simple devices. They consist of a light source (LED) coupled to a photo transistor.  The input data signal turns the LED on and off which causes the photo transistor to switch on and off. The LED and photo transistor are completely isolated from each other electrically. The data source (talker) must provide sufficient current and voltage to power the LED. A current limiting resistor in series with the LED is generally used for protection.  The advantage of opto-isolated inputs is that virtually any type of driver can activate them.




Here are the possible connections...

Differential to Differential

Single ended to Single Ended

Single ended to Differential

Differential to Single ended

When multiple listeners of different nature (single-ended vs. differential) are to be connected to a talker port, the same connection rules apply. Here, two differential and one single-ended listener are connected to the differential output of a multiplexer.

Multiple Talker Circuits.

Where a single listener requires data from multiple talkers, a data multiplexer or combiner will need to be installed.  Data multiplexers buffer the input sentences from each talker, and provide a single data stream that may then be connected to multiple listeners.
There are a number of companies that provide multiplexers and these days, you can even get a multiplexer that outputs Nmea 0183 Sentences via Wifi.

There is a practical limit to the number of talkers that can be combined based on the available bandwidth and the number of sentences that each talker transmits.  Products are available that combine up to four talkers and replicate the combined output into four or more new talker circuits, each capable of supporting multiple listeners.   Here you see a typical setup using a Brookhouse multiplexer which has also the capability of converting Seatalk to Nmea as well.

Typical Multiple Talkers Combined to Single Listener

But what do we do if we want to mix our older hardware which runs on the older "bus" of Nmea 0183 and the newer Nmea 2000?
Well, I can only find two devices that do this directly. Presented here are......
Actisense
Here's some of what the company says... 
The Actisense® NMEA 2000 to NMEA 0183 Gateway is the easiest way to link between a boats old and new data networks. The NGW-1 can convert NMEA 0183 data into NMEA 2000 data and vice-versa.

The NGW-1 allows current NMEA 0183 equipment to be kept, or allows the latest NMEA 2000 equipment to be incorporated into the NMEA 0183 system. Once the single cable NMEA 2000 bus system has been installed, data from any node on the bus can be listened to by any other, including any NMEA 0183 instruments connected using an NGW-1.

The NMEA 2000 network acts like a bi-directional multiplexer, allowing all data sources to talk and listen to each other.

At the moment, this seems the simplest way of achieving a bi directional talking of the two Nmea standards.

Amec NK-80

An alternative to Actisense would be this product from Amec
NK-80 is a gateway between NMEA 0183 electronics devices and NMEA 2000 device/network. NK-80 allows users to connect NMEA 2000 network with their existing NMEA 0183 devices. 

Key Features of NK-80 according to the company: 

‧Upgrade NMEA 0183 equipment to NMEA 2000 
‧Conversion between NMEA 2000 and NMEA 0183 
‧Full NMEA 2000 compliance 
‧Full NMEA 0183 compliance 
‧Compact size, easy for installation 
‧Isolation between NMEA 0183 and NMEA 2000 
‧Fully galvanically isolated for electrical spike protection

One final way that may prove beneficial to some. There are now devices such as MFD's that have both NMEA 2000 and NMEA 0183 in and out. It may seem odd that the Raymarine E-Series can input/output data via good old NMEA 0183, SeaTalk, (similiar to NMEA 0183) SeaTalk2 (actually NMEA 2000), and SeaTalk HS (actually Ethernet).  So the E’s (and C’s) do something called data bridging. It works by taking data, if it is not on a particular level, and converts and sends the data on at the higher level. I suspect it is converted up to the higher level, but not converted down. Perhaps someone can leave a comment and advise as to whether this is true?

That's it for now. Hopefully soon, I'll post about Raymarine and their Seatalk interface, along with it's interface with NMEA2000 and NMEA0183

Spar Hitch

The Spar Hitch is the second knot I teach my guests when they come and stay on the boat. Of course, the first knot everyone learns is the bowline. The Spar Hitch also goes by other names and among them is the Ground Line Hitch. Check out also the Millers Hitch and the Constrictor Knot. They all do the same job really. And I only teach a clove hitch in passing now. I think the Spar Hitch is just as easy and more secure.

The knot starts out like a clove hitch. One turn around the spar and over the standing end and back over the spar. You can do this either to the left or the right.

Take the bitter end and pass under the spar and over the first completed turn. (A clove hitch here would go under that first completed turn.)
Then take the bitter end and pass it under the start of the first turn.

Finally take both the standing end and bitter end and snug the knot tight. The knot can be made for quick release by placing a loop in the bitter end before placing under the start of the standing end.
I use this for securing items to railing or life lines. Even fenders secured this way on small life lines will not slip. Quick, easy and secure.


Finally, below are some variations of this hitch.

Cruzpro

Shortly after writing about my Paddle Wheel Dilemma, Mark Corke also wrote about the Cruzpro (also mentioned in my blog) and offered up some pro's and con's. Go over to Mark's blog and have a read. He is going to buy one and install it. Keep an eye on his blog site for updates and reports of this interesting device.

Paddle Wheel Transducer Dilemma

A lot of you out there will know of the frustration when your paddle wheel gets clogged, and fails to work. Pulling the thing out (if it is a thru-hull) to clean is not only a chore, but can let in a bit of sea water.
I have an Airmar DST800 (Depth, Speed, Temperature)  which I bought around 2005. It was for Raymarine ST60 instruments and did the job fairly well. When removing the transducer, I get an ingress of water because it does not have a self closing  valve which would close as the transducer is removed. I believe (I have been told, correctly or incorrectly) this is still the case for the Raymarine  DST800; and yet most of the other transducers of this model (post 2005) have the self closing valve. See their brochure here for the DST800. I was told the transducers were changed after 2005  so that they have the self closing valve, BUT not the Raymarine version. A little research was required.

My instuments (ST60 Tridata) work by taking an analog signal input from the transducer. My ST60 will only display seatalk input if changed to a repeater display. It will not display nmea 0183 or 2000 data, UNLESS one can convert that data back to seatalk (1)

My choices after some contemplation were
 1. Stay as I am
 2. Change to a new DST800  with nmea 0183 output,  and get a nmea 0183 to Raymarine
 converter so I can have the self closing valve.
 3. Purchase a new DST900-EM which has no paddle wheel and picks up speed by electromagnetic induction, also with a self closing valve

Considering those choices, here are the problems.

1. There are plenty of multiplexers out there that will convert Seatalk to nmea 0183; but I've yet to find one that converts nmea 0183 to Seatalk. This conversion would not be needed if the new DST800 has BOTH a self closing valve and analog output. The brochure here says it only comes in nmea 0183 & 2000 outputs.
2. After contacting an Airmar dealer through email, the DST900 isn't on the market as yet. Here's what he said.(Oct. 2012) "The DST900 is still not available yet from Airmar. No date or cost on the release." AND (as the brochure reads only nmea 2000) I would then have to change nmea 2000 to nmea 0183 and then to Seatalk or analog signal. Can't be done, I think. More about that later. I made some more enquiries.

Notwithstanding that statement, I'm sure they will be released soon and have included here a little of what Airmar has to say about the product. For those with nmea 2000, a great choice when it is released!

Here's Airmar's blurb. Check their Brochure here.

Airmar’s NEW DST900-EM is the industries first all-in-one depth, speed, and temperature sensor with no moving parts. The NEW innovative speed sensor circuitry creates a magnetic field in the water. Speed is accurately measured by the voltage created through 

conductive properties of water, combined with the forward motion of a vessel. With no moving parts, the DST900-EM is capable of accurate readings at all vessel speeds. What sets the DST900-EM apart from the traditional speed paddlewheel is the excellent 

accuracy at very low-speeds between 0.5 and 5 knots (0.6 and 6 MPH)—an important feature for sailboat racing. The DST900-EM’s accuracy at high-speeds up to 50 knots (57 MPH) makes it an important sensor for powerboats. By eliminating the traditional paddlewheel, there is no fouling, and drag is reduced to a minimum of 6.3 mm (0.25”) below the hull due to the low-profile housing.  

Rated at 100 W power, the 235 kHz depth transducer provides depth readings in as little as 0.45 m (1.4’) of water and can reach depths up to 180 m (600’). The narrow-beam of this transducer will 

deliver accurate depth readings at speeds over 35 knots (40 MPH). 

Additionally, the 235 kHz frequency prevents mutual interference with other echosounders on the vessel. 

The DST900-EM’s fast-response water temperature sensor provides ±0.2°C (±0.1°F) of accuracy to help in finding the optimum conditions for fishing or swimming. Airmar’s patented housing design incorporates the popular self-closing valve. When the transducer is removed for cleaning, the valve minimizes water flow 

into the boat. 

The lightning-fast processor inside the DST900-EM makes calculations every second, so it can respond quickly to changes in speed, depth, and temperature. This data is then sent to the NMEA 2000®network via a single devicenet cable for an easy plug-and-play installation.

Sounds like it will just support nmea 2000,

But recent enquires put a different light on the question of legacy formats. A recent email had this to say...  "The DST900 most likely will have the self closing valve. The DST900 will be capable of outputting Analog, NMEA 0183 and NMEA 2000 so it should cover all your needs including working with the ST60.

At this point we still do not know when it will be released." 

So if I wait long enough, maybe this will be my solution of choice. Sometimes this is called vapor ware.

So, I'm no closer to solving the paddle wheel "blues". However....

Here's another solution. Don't have a transducer at all!!

This solution by Cruzpro here is great if you don't mind SOG instead of STW .

The CruzPro SOG1 takes NMEA 0183 data from a GPS and creates an analog paddlewheel signal so you can display Speed Over the Ground (SOG) on a standard speed log without a transducer.

SOG1 NMEA 0183 to paddlewheel signal converter

The SOG1 creates an analog paddlewheel output signal from a GPS NMEA 0183 $GPRMC sentence so you can display Speed Over the Ground (SOG) on a standard analog or digital speed log.

The SOG1 replaces a thru-hull or transom mount paddlewheel speed transducer and provides Speed Over the Ground in place of Speed Through the Water.

No more cleaning of paddlewheels to remove marine growth or weeds.

Provides a more accurate estimate of time to get to your destination since it is not affected by water currents and provides a resolution of 0.01 knots from 0.00 to 60.00 knots.

The SOG1 is powered by 12VDC and draws less than 0.020 amps.

NOW,

Back to to Airmar's current selection; Thinking that the new DST800(V) isn't available for Raymarine instruments, I came across the following info in this Newsletter. It appears that perhaps they do have a new DST800 that will do the ST60 instruments AND the self closing valve. Read below their blurb....

The DST800 Retractable TRIDUCER® Multisensor is now available with

a VALVE

The industry’s only depth, speed and temperature retractable transducer is

now available with a valve! The DST800V meets customer demand for our

patented valve assembly that prevents water from rushing into the hull when

the insert is removed. And the addition of a valve lets boaters service the new

DST800V while the vessel is in the water, saving time and money!

Offered in NMEA 2000®, NMEA 0183 or Analog versions, the new DST800V simplifies any

installation by delivering three readings while having only one hole drilled in the bottom of the

boat. These three important readings can then be displayed on instruments, echosounders,

NMEA repeaters or Network navigation systems.

The new DST800V includes:

• Airmar’s patented self-closing valve assembly.

• Two O-rings, one at the top and one at the bottom for a water-tight seal.

• Industry standard 2” thru-hull hole size.

• NMEA 2000®, NMEA 0183 or Analog versions available.

Although the new DST800V contains Airmar's popular TRIDUCER® insert, the original DST800inserts cannot be retrofitted into the new housing with a valve. This is because all DST800 insertsmanufactured prior to November 2005 have ribs and an alignment key. If an older style insert withribs is pushed into the new P617 housing (which contains a valve), the insert will damage thevalve assembly.

However, all DST800s manufactured after November 2005, do not have ribs or an alignment keyon the insert. These can be retrofitted into existing installations that have a plastic P17, bronzeB17 or stainless steel SS577 housing. To insure proper sealing when installing a DST800 in aP17, B17 or SS577 housing, the yellow O-ring at the top must be replaced with a black O-ring.

Sooooo; my choices now are, I can wait for the NO paddle wheel DST900 and change out (choosing the analog version). Change to the upgraded DST800 (with self closing valve) but have to pull it out occasionally to clean the paddle wheel ( but not suffer the ingress of water due to a self closing valve), or go no transducer and loose the depth and water temperature in the process. Hmmmm, I think I will just sit and wait another year!
What would you do?

Home Handyman Aluminium Repair

Have you ever had an aluminum repair or 'thing" you wanted to make, but thought you had to use a TIG welder, which you don't have, and end up taking it to someone who has?
Then try this product; HTS2000


Other products (rods) that do a similar job are Durafix and Alladdin 3 in 1. Shop around with the products to get the best price. I've heard of prices from $5 to $60 per pound for very similar products

All of these rods are aluminum brazing rods and they are made basically from aluminum and zinc
You can use propane, oxy/propane, oxy/ acet. The smaller and thinner the pieces, the better it is to stay away from the O/A and use the mapp (preferred) or propane unless you have the correct size tips as the O/A can get to the melt temp really quickly. Use a very fine tip (00 or 0) when working with 1/8" or thinner material with O/A.

If you can braze then you can use this product.

Don't use this product on high temperature items. Even though it says you can do cylinder heads and exhaust manifolds, I wouldn't. Use a TIG instead.

And then of course there is stainless steel brazing rod, of which there are a few varieties. Most all contain silver as one of the alloys. You can do the search to find out what's out there.

These items lend themselves to emergency repairs on a boat, or a DIY project that doesn't need the expense of a TIG welder. You would have to make a decision as to whether a TIG is required or brazing will do. Keep in mind that if the brazing doesn't work, and you have to use TIG, all the brazing work will need to be ground out, before you can use the TIG. 

My intention for my next cruising season, is to carry a propane torch that will run off the BBQ gas tank, and some of these rods for emergency repair. Any comments?