NMEA 2000 On/Off Switch?

[nige]

Hey All,

I have a question about NMEA 2000 devices and the ability to switch off devices that have no on/off switch.

I have two needs for this:

1. This setup will be on a small cat and I was hoping to be able to manually (or with a tilt switch) power on/off the Speed/Depth/Temp transducers depending on the tack.

2. We have a number of NMEA 2000 devices (AIS for example) that I do not need to be powered on all the time, but I am not sure how to switch them off independently if they are not powered by the bus.

I googled around but could not find any specific devices for this and I am sure I can strip the cable and put a switch on the power/ground, but was hoping there would be a cleaner solution etc.

Am I misunderstanding something or does no one else have the need? (I only have the need because of the type of race we are doing, so would not be surprised).

Thanks hive mind!

 

[allene222]

You might see what is there at the system level. I looked into this a little and found that my TactTick system can have two depth and speed senders and will switch between them based on apparent wind angle. Perhaps other systems will do this automatically as well.

Not a nmea-2000 expert but my understanding it that this is a terminated buss system so you might have to put the things you want to switch off at the end of the buss and switch in a new termination when you remove the off devices. Or it could be that the buss can tolerate having off devices connected. Worth checking this before settling on a solution.

Best of luck.

 

[Alex W]

NMEA 2000 has 5 wires: CAN+, CAN-, V+, V-, ground/shield.

You can switch the two power wires (normally red and black) or just the positive to turn power on and off to a device without affecting the bus. You shouldn't put any switches on the CAN bus wires (blue and white on my Raymarine system) or the shield. The devices that are powered off but still wired into the bus won't affect termination.

Some companies like Raymarine add a 6th wire that is used for NMEA 0183 or other downlevel buses.

 

[PeterSailor]

The termination resistor are for the data bus only. You can use NMEA2000 power isolator connector, like the Garmin 010-11580-00, to split the power feed in three sections of N2K network and maintain a single data bus.

Terminator ----- Left_helm ---- Isolator ---- Right Helm ----- Isolator ------ All_sensor_&_others ------- Wind Sensor with terminator

 

[weightless]

^^^ Is is likely that sticking two of the same type of node on the bus at the same time would crash the bus? Just wondering how critical it would be for the OP to switch out his old speed/depth/ before switching in the new.

 

[Expedition]

Something like this may help

http://www.tinleyelectronics.com/products.htm

http://www.stowemarine.com/gravity.htm

 

[nige]

Thanks, the NMEA changeover switch looks perfect for the speed/depth issue. (Something else to add to the purchase list though).

PeterSailor - thanks, those isolators look like they will at least allow me to have a group of instruments that we can turn off.

Appreciate the thoughts!

 

[Alex W]

^^^ Is is likely that sticking two of the same type of node on the bus at the same time would crash the bus? Just wondering how critical it would be for the OP to switch out his old speed/depth/ before switching in the new.

No, it won't "crash the bus". It will either cause confusion with both reporting, or the system will continue to pay attention to the original one depending on the exact equipment used.

 

[weightless]

^^^ Is is likely that sticking two of the same type of node on the bus at the same time would crash the bus? Just wondering how critical it would be for the OP to switch out his old speed/depth/ before switching in the new.

No, it won't "crash the bus". It will either cause confusion with both reporting, or the system will continue to pay attention to the original one depending on the exact equipment used.

Thanks. I asked because of "Message IDs must be unique on a single CAN bus, otherwise two nodes would continue transmission beyond the end of the arbitration field (ID) causing an error." Sounds like it's not an issue for N2k.

 

[Alex W]

^^^ Is is likely that sticking two of the same type of node on the bus at the same time would crash the bus? Just wondering how critical it would be for the OP to switch out his old speed/depth/ before switching in the new.

No, it won't "crash the bus". It will either cause confusion with both reporting, or the system will continue to pay attention to the original one depending on the exact equipment used.

Thanks. I asked because of "Message IDs must be unique on a single CAN bus, otherwise two nodes would continue transmission beyond the end of the arbitration field (ID) causing an error." Sounds like it's not an issue for N2k.

It depends on the length of the message.

Depth (PGN 128267) and speed messages (PGN 128259) are both one packet long, so there is no potential for confusion.

Two transducers outputting different data and intermixing longer messages (greater than one packet) would cause confusion but wouldn't "crash the bus".

Raymarine has an arbitration mechanism to handle multiple devices of the same type on NMEA 2000, but I don't know if this is a generic part of the spec or something proprietary.

 

[Mark Morwood]

I'm curious about this. I have a catamaran and have two speed transducers and two depth transducers on my NMEA 2000 bus both on all the time. My Garmin chartplotter and Garmin displays see them both as independent sources and let me choose which one I want to display/use as speed/depth source on each head display. I have a Raymarine i70 display on the network which also shows the same selection options. I don't know the details of the protocol, but because of this behavior I had assumed that this was well supported using the device's id to distinguish sources of the same type of data.

 

[nige]

Mark - I agree, I think its pretty common and most MFRs give you an option to select which input you want to look at. (Instrument mfr.'s having software to watch 2 and switch calcs based on AWD seems less common, especially in the budget ranges, but that is not really surprising).

 

[Alex W]

NMEA 2000 is build on J1939, and that is described pretty well here:

http://www.simmasoftware.com/j1939-presentation.pdf

Slide 39 goes into address negotiations.

That eliminates duplicate IDs, but I think a different PGN is used to get all devices on the network to identify themselves (it looks like it might be 59904).

Raymarine doesn't seem to have supported this for too long, on my network my X5 autopilot prevents device negotiation from working properly (and I don't have any duplicate devices to really experiment with). The X5 isn't that old of a product.

NMEA 2000 is a closed protocol and only documented to those who pay for it and get devices certified. There is a reverse engineering of it here:

https://github.com/canboat/canboat/blob/master/analyzer/pgns.json

I'm not an expert in it by any means, I just started playing around with dumping network traffic to learn the format. I plan on updating my DIY wind instrument to NMEA 2000 and also creating a NMEA 2000 to WiFi device so that we can see transducer data from phones or tablets. Longer term I may also use the same device with a SIM to let me check on wind speed at the boat from anywhere (the closest wind station only reports data every hour).

 

[Talchotali]

Fast forward seven years...

An AIS transceiver receives VHF digital data on potential local targets (and sends host boat data) when powered. It sends target data info on the NMEA 2000 bus to whomever is listening.

Garmin chartplotters after power-up report this data as warning messages, regardless of how the system was configured at last power down. This is considered a safety feature (see below).

This means in a marina of a 1000 boats with 100 active AIS transmitters you have to quiet 100 messages before you can gain control over the chartplotter system. If a message is displayed, the touch screen input to the display in inhibited. So you have to play with the messages until you can work your way to the turn-off alarm function on the display with each power-up. You have about three seconds between messages when the display will accept a touch input. With the next message, the display inputs are inpoperative until that message is cleared.

I can see Garmins logic in doing this (fail-safe operation after a inadvertent de-powering). However, disabling input of the display when any message is active creates the "wack-a-mole" senario above. A system fix for Garmin would be: if the messages showed up in their own independent window (think Windows) and the regular active menu could be navigated, one could just navigate to the AIS off or AIS alarms silent funciton and be done.

I currently have a power switch on the AIS unit so I can shut it off electrically when I bring up the Garmins, turn off AIS, then power up the AIS. However, if I forget re-power AIS, I have defeated that system which generally is designed to be powered and broadcasting all the time.

So a battle of the fail-safe philosophies.

Inhibiting NMEA 2000 messages coming from the AIS to the Garmin chartplotter would solve this issue. The AIS could keep transmitting and the chartplotter can be quickly configured at startup. No "wack-a-mole".

Is there a device that fits between two NMEA 2000 T-junctions that allows a switch input to inhibit message traffic? Or can I tap into one of the data wires in a NMEA 2000 cable to interrupt data messages being sent with an inserted switch, and then allow through message traffic with the flip of a switch (re-connecting the interrupted data wire circuit).

Other boats don't seem to have this problem, so perhaps Simrad, Furuno, B & G and Raymarine have a smarter AIS failsafe or a more configurable system.

Garmin AIS Alarms Returning to the ON Position After a Power Cycle | Garmin Customer Support

Garmin Support Center is where you will find answers to frequently asked questions and resources to help with all of your Garmin products.

support.garmin.com

AIS Alarms Returning to the ON Position After a Power Cycle​

The Automatic Identification System (AIS) is a marine vessel-tracking system used for collision prevention. AIS-compatible chartplotters will display dangerous nearby vessels on the chart. Whenever a connected AIS device detects a possible dangerous target, an alarm will sound and alarm message will show on the chartplotter.

Garmin offers three AIS devices that can be interfaced with a compatible Garmin Chartplotter, the AIS 300, AIS 600 or a VHF 300 AIS.

If desired, the audible alarm can be disabled for the AIS system, though the alarm message will still show on the screen. To disable the audible alarm, please follow these steps:

1. Start from the Home screen
2. Select Configure
3. Select Other Vessels
4. Select Collision Alarm or AIS Alarm
5. Select Off

The AIS alarms will automatically turn back on after a power cycle of the chartplotter. This is by design and is done so for safety reasons.

 

[willsailforfood]

Old thread, but you may want to look at this:

Maretron Mini-Powertap

This is what we use on the NMEA2000 network, wired to the 12v panel. This provides independent power to each side of the NMEA2000 network, so you get twice as much available power for devices on each of the two legs of the backbone. Place it in the center of your backbone.

 

[Go Left]

Hey All,

I have a question about NMEA 2000 devices and the ability to switch off devices that have no on/off switch.

I have two needs for this:

1. This setup will be on a small cat and I was hoping to be able to manually (or with a tilt switch) power on/off the Speed/Depth/Temp transducers depending on the tack.

2. We have a number of NMEA 2000 devices (AIS for example) that I do not need to be powered on all the time, but I am not sure how to switch them off independently if they are not powered by the bus.

I googled around but could not find any specific devices for this and I am sure I can strip the cable and put a switch on the power/ground, but was hoping there would be a cleaner solution etc.

Am I misunderstanding something or does no one else have the need? (I only have the need because of the type of race we are doing, so would not be surprised).

Thanks hive mind!

Why would you want to do that to a small cat. PETA will be on your ass and the cat will likely scratch the living shit out of you.

 

[b393capt]

With the exception of booting up the network, I wouldn't expect MFD's or anything else listening on the bus to simply accept messages from two different speed sensors just because one becomes present while the other disappears.

 

[SASSAFRASS]

Have had issues on the power up sequence with Simrad BnG. Seems like it doesn't always like it when you stray from backbone and all devices then MFD. AP in particular wants network on first.