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NMEA GPS input to ST4000+

Andrew G

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1 Apr 2013
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Hi all. I am trying to input a GPS’ NMEA 0183 output into the “NMEA In” terminals of my Raymarine ST4000+ Autopilot. By my reading of the manual, the GPS’ NMEA + (& -) should go into the AP’s NMEA+ (& -) and the AP then outputs the data as SeaTalk (ST) on the ST bus. BUT I get no positional or time information on the ST bus. (I have tried switching the + and –s)
I cannot see any configuration changes etc. that I have to make - does anyone have first hand experience in this?
(One option is that my AP is partially stuffed.)

{By way of background, my ST GPS (Raymarine 120) died because if a $2.50 internal battery. I have replaced the GPS with a reputable 50 channel NMEA-out unit. If I connect the GPS as NMEA In to my chartplotter it works (but does alarm a few times an hour – another issue - I suspect not the GPS’ fault). There are always 12+ high signal-strength satellites in view. I’ve been using the same cable and connections for input to alternatively the chartplotter or the ST4000+. The chartplotter does successfully convert the NMEA data to ST and puts it on the ST bus. I had hoped to not need to have the chartplotter switched on at all times by simply inputting the NMEA directly into the NMEA In of the AP.}
Regards, Andrew
 

chewi

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I have always wondered how the industry got in such a mess with labelling NMEA. The protocol is standardised(ish) but not the names of the connections.
It helps to understand a little of how it works.

NMEA sends packets of info out, (typically on NMEA+ or NMEAOUT) and takes an acknowledgement back (typically on NMEA- or NMEA IN) before the next packet is sent. Without both it might work in some way, but will malfunction.

The eacknowlewdgement is sent by the receiving NMEA, on NMEA OUT, so the OUT on one musdt be connected to the IN in the other.
both these signals are withrespect to a common (typically 0V,GND or -VE), which I suspect you are missing.

Yours should work by connecting NMEA+ to NMEA- and vice versa, but you will also need the common 0V.
 

pandroid

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You don't say what you are connecting to what, but it may be the issue that the St4000+ is receiving the data but not retransmitting it. In our case, the NMEA was connected to the course computer, not the ST4000+ Control head but we had a similar problem. It turns out that, although the unit receives and processes the sentences, it doesn't forward some sentence types onto the Seatalk bus. Time (ZDA) is definitely one of these and we had to end up buying the Raymarine Interface box (which handles all the sentences) to get this data to the chartplotter.

If you are connecting the NMEA direct to the St4000+ Control head, an analysis of the manual indicates that pure position and time, (GLL and ZDA) are not processed by the control head, only sentences like BTW and COG etc.

You cant treat the device like an MNEA repeater. It only deals with sentences it thinks it needs.
Ivan
 

Andrew G

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Ivan, thankyou for your reply (although it is not what I wanted to hear, if you know what I mean).
Your experience certainly matches the observations.
Did you get the 85001 Interface Box and how is it?
For others’ information, I’ve copied part of the ST4000+ manual (format has screwed a little). You can see where I interpreted this as reading NMEA RMC and outputting SeaTalk equivalent. It doesn’t appear to do it in practice. (and I do appreciate that navigation does require more than the sentences listed so it was never going to be a complete solution. My options would appear to be to revert to using my chartplotter all the time or buying an Interface Box as there are no NMEA to SeaTalk YAPPs on the way.)
Cheers, Andrew

“. . .
NMEA data formats
TheST4000+ can decode the following NMEA 0183 navigation and
wind data:

Information NMEA 0183 data
Course Over Ground VTG, RMC, RMA
Speed Over Ground VTG, RMC, RMA
Cross Track Error APB, APA, RMB, XTE
Bearing to Waypoint APB, BWR, BWC, RMB
Distance to Waypoint BWR, BWC, RMB
Waypoint Number APB, APA, BWR, BWC, RMB
Apparent Wind Speed VWR, MWV
Apparent Wind Angle VWR, MWV
Speed Through Water VHW
Depth DBT
Water Temperature MTW

Note: The autopilot only decodes the last four characters of waypoint names.
This means that the last four characters of long waypoint names must be
unique for the waypoint advance function to work.

Transmitting NMEA data on SeaTalk
If the ST4000+ receives any of the NMEA data shown above, and the
equivalent data is not present on SeaTalk, it will transmit the data onto
SeaTalk to make it available to other SeaTalk instruments:
• the ST4000+ transmits depth information in the units defined by
the first page in the data page rollover
• the ST4000+ always transmits water temperature in °C . . .”
 

AngusMcDoon

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I know how fast I'm going, but not where I am
NMEA sends packets of info out, (typically on NMEA+ or NMEAOUT) and takes an acknowledgement back (typically on NMEA- or NMEA IN) before the next packet is sent. Without both it might work in some way, but will malfunction.
That's not correct at all. Firstly NMEA0183 connections of all versions are one way only, the talker sends a packet and knows nothing about what happens to it. There may be one or more listeners on the line or none at all. The talker doesn't care. There is no acknowledgement. It just keeps on banging out its data every so often.

Now to why there are different labels on NMEA0183 connections. NMEA0183 started out in it's first version as single ended like RS232. This means a data line and a ground. You connected data out on the talker to data in on the listener and then connected the grounds. Then from version 2.something onwards NMEA0183 became differential similar to RS422 at the talker and opto-isolated at the listener. You had NMEA+ and NMEA- on talker and listener and you connected them together. No ground connection is necessary. The signal at the receiver goes through the opto-isolator which the signal itself powers. The listener can be completely floating compared to the talker. NMEA called these connections NMEA+ and NMEA-. Some people call them by the RS422 names A and B. Other manufacturers label them DATA+ and DATA-, or just + and -. To complicate things further, some manufacturers use a later version of the standard for their message format but still transmit in the old fashioned single ended way and have DATA and ground labels. Garmin are one such manufacturer and B&G did the same on some products. There's a good reason to do this which I won't go into here. My NMEA multiplexer YAPP has both types of output.
 

chewi

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That's not correct at all. Firstly NMEA0183 connections of all versions are one way only, the talker sends a packet and knows nothing about what happens to it. There may be one or more listeners on the line or none at all. The talker doesn't care. There is no acknowledgement. It just keeps on banging out its data every so often.

Now to why there are different labels on NMEA0183 connections. NMEA0183 started out in it's first version as single ended like RS232. This means a data line and a ground. You connected data out on the talker to data in on the listener and then connected the grounds. Then from version 2.something onwards NMEA0183 became differential similar to RS422 at the talker and opto-isolated at the listener. You had NMEA+ and NMEA- on talker and listener and you connected them together. No ground connection is necessary. The signal at the receiver goes through the opto-isolator which the signal itself powers. The listener can be completely floating compared to the talker. NMEA called these connections NMEA+ and NMEA-. Some people call them by the RS422 names A and B. Other manufacturers label them DATA+ and DATA-, or just + and -. To complicate things further, some manufacturers use a later version of the standard for their message format but still transmit in the old fashioned single ended way and have DATA and ground labels. Garmin are one such manufacturer and B&G did the same on some products. There's a good reason to do this which I won't go into here. My NMEA multiplexer YAPP has both types of output.
Well thanks for that Angus, I have misunderstood.( I have already eaten humble pie today!)
I have had two garmin GPSs (a 48 and a 152), connected to send the waypoints from one to another, and as I recall unless I connected the NMEA+ on the receiver to the NMEA- on the sender as well as a common ground I only got some of the waypoints, so it seemed the acknowledgement I referred to was related to buffer size.
 

pandroid

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Yes. I have the 85001. Its works fine. My setup is a ST4000+ Control Head, Type 100 Course Computer, Gyro, and RL70 CRC radar/plotter. The GPS is a Garmin 128. Originally I had the Garmin wired to the Course Computer which worked, but the time to destination and some other stuff on the plotter wouldn't work. I routed the GPS through the plotter for a while, but by routing it through the interface box, this resolved the issue. It also gave me an RS232 output to route to a PC.
Ivan
 

Danbury

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If anyone wants some snazzy diagrams to explain it... the August 2013 edition of Yachting Monthly has it all... even I understood it !
 
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Andrew G

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1 Apr 2013
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Melbourne, Australia
Hi LadyInBed, yep they are all 4,800 (the designs well and truly predate 38,400) - I am convinced that the ST4000+ just doesn't do what I want it too.
Danbury - I must have missed that edition. I was going to ask if was legitimate for "someone" to scan and post the article but I came across this instead. I assume this is the basis of his article?? Well done Tim. http://www.timbartlett.co.uk/briefing.html#NMEA_0183

I have now purchased a Raymarine box (their E85001) – it may be one of the last ones in Aus. This should solve my problem.
Thanks to all and cheers, Andrew
 
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