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gadgetPool.de :: View topic - NASA NMEA Senders won't work with Mux with Seatalk + USB
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NASA NMEA Senders won't work with Mux with Seatalk + USB

 
Post new topic   Reply to topic    gadgetPool.de Forum Index -> Nmea Multiplexer with SeaTalk I/O
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OldSalt
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PostPosted: Thu Mar 17, 2016 11:10 am    Post subject: NASA NMEA Senders won't work with Mux with Seatalk + USB Reply with quote

Hi,

Sorry but I thought I had already posted this query before but I am unable to find it on this forum and so I am re-submitting it here!

I purchased a "NMEA Multiplexer with Seatalk and USB port" from you some time ago but only just got around to fitting it. It works just fine with my Seatalk instruments and also with my Garmin GPS128 but refuses to work with any of my NASA Marine NMEA devices eg... "Wind Instrument", "Compass" and "A.I.S. Engine".

All of these senders have a NMEA 0183 output which has worked perfectly for several years now using either direct RS232 computer input or via a variety of USB to RS232 converters. However, when I connect any of these instruments to the NMEA Input ports on the MUX no output is recorded on the NMEA Monitor screen. Further, when I connect my Laptop to the NMEA output of the NASA senders, using serial port monitoring software, I can read the NMEA sentences outputted from the devices perfectly. However, as soon as I plug the line into the NMEA input socket on the MUX, two things happen!

1. The output recorded on the Laptop monitoring the Sender's NMEA output ceases immediately and

2. The amplitude of the signal appears to reduce significantly as measured using a digital voltmeter (unfortunately, I don't have a scope)

I have tried changing the sender -ve to Grnd and back but the same things happens in either case. I have also tried connecting these senders to the Mux port that I am using for the Garmin GPS (which works perfectly) but the NASA senders still show the same symptoms.

It occurs to me that the Opto-isolators in the MUX inputs are probably demanding more power than these NASA senders can deliver, hence the drop in output volts.

I was wondering if this problem has been raised before and if so, is there is a solution to it? I am tempted to make an "Emitter Follower" circuit to match what appears to be a high output impedance from the NASA senders to what appears to be a much lower input impedance on the Mux NMEA inputs! Is this a reasonable solution to the problem or have I missed something fundamental in setting things up?

Regards,

Keith
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OldSalt
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PostPosted: Tue Mar 22, 2016 11:24 am    Post subject: Not Yet had a reply! Reply with quote

Hi Frank,

Further to my last post, and in the absence of any reply I have constructed a 5v "Emitter Follower" circuit powered by a 12v to 5v dc to dc pcb isolated power supply {XP Power 1K 1205SA}. The emitter load resistor is 1k ohm and the transistor is a BC 548BU. It appears to be working correctly when connecting the "base" between the +5v rail and the -5v rail the output across the emitter resistor follows the input as expected. Again, with the base connection disconnected altogether, there is zero volts output as expected.

As yet, I haven't tried it out as a "current power booster" between the NMEA output from my NASA Sender {Clipper Wind} and the NMEA input port on the MUX.

Since the 5v supply is totally isolated from the ship's battery, is there any reason why this emitter follower cannot be directly (dc) connected between the the NMEA sender and your MUX? I'm just a bit nervous as I don't want to damage any of the NMEA input ports to the MUX.

An early reply would be very much appreciated. Thanks.

Kind regards,

Keith[/i]
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OldSalt
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PostPosted: Fri Mar 25, 2016 7:15 pm    Post subject: Tried the Emmitter Follower ~ It Works fine! Reply with quote

Hi Frank,

In the absence of a reply to my previous posts, I thought you may be interested to know that I decided to give my 4-channel emitter follower power amplifier a trial to boost the input to the Mux from my "NASA Marine" NMEA Senders.

I have used 3 emitter followers {channels}, one for each of the Wind, Compass & A.I.S. NMEA Senders. I am pleased to report that they now all work perfectly with no sentence errors noted after a 3 hour test using "check-sum" validation.

Conclusion:- The NASA Marine NMEA Senders do not deliver sufficient current output to drive the "NMEA Multiplexer with SeaTalk I/O". The simple addition of an emitter follower current gain amplifier corrects the problem.

As I have said previously, The "SeaTalk" and "Garmin GPS" work perfectly without any input modification. I don't know if any other manufacturer's NMEA 0183 AIS, Compass & Wind instruments also suffer from low current, high impedance outputs. If so, my solution may be appropriate for other senders as well!

Kind regards,

Keith
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FWallenwein
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Joined: Mar 26, 2006
Posts: 419
Location: Mannheim / Germany

PostPosted: Fri Apr 01, 2016 11:54 am    Post subject: Reply with quote

Hello OldSalt,
sorry for not replying to your posting. I must admit, I simply overlooked it.
Unfortunately I don't get a mail, when a new topic is opened in this forum.
So I look at it now and than - but I did not see you postings. Sorry again.

Regarding your solution for NASA Marine NMEA Senders.
We had that problem with TackTick NMEA interfaces as well and other users posted two different solutions

See: Anschluß NMEA Interface Tacktick.
This thread starts in german, but from the third posting on we switched to english. ( Just changed the title )

Would you provide a circuit diagram for the solution you found ?
I'm sure this would be helpful for other users as well.


Thank you for posting,
Frank
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