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NMEA Interface Problem - Thom or someone else to help

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NMEA Interface Problem - Thom or someone else to help

Old 12-17-2002, 07:02 PM
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Default NMEA Interface Problem - Thom or someone else to help

Problem is NMEA interface between GPS and radar.

I have a Lowrance LCX-15MT. It has NMEA version 2.0, with COM-1 and COM-2 available. COM-1 has Transmit (Yellow), Receive (Orange), and Shield (Ground). COM-2 has Transmit (Blue) and Shield (Ground).

I also have recently installed a Si-Tex T-721 color radar. It has two NMEA interface ports. One requires an option cable, and the other is included with the main power connector. The included one has a RED wire designated NMEA (A), and a GREEN wire designated NMEA (B). This included interface is shown in the manual to allow connection to external NMEA equipment such as GPS, LORAN, etc.

I have tried connecting the Lowrance COM-2 output (Blue and Shield) to the Si-Tex input (Red and Green, respectively), but did not get any input to show on the NAV screen on the SI-Tex.

Questions:

1) Should these wires be connected this way, or do the shield and NMEA (B) actually go a common ground on the boat? Or some other wiring scheme?

2) The Lowrance has some detailed NMEA settings, including BAUD rates of 1200-115200 (default 9600), and specific NMEA "sentence" slections. Not sure if factory defaults will work, or if changes required. Comments/suggestions?

3) The Si-Tex has NMEA Preset adjustments that allow changing the priority of the NMEA data to be read by the radar. In other words, the NMEA sentence priority can be changed. Comments/suggestions?

Would greatly appreciate any assistance available in getting the Si-Tex to accept NMEA input data from my Lowrance, so I can display NAV info on the Si-Tex while using the full Lowrance screen for sonar, as well as show waypoints, etc on the radar screen.

Thanks,
Brian

2002 GW Islander 270 - 2001 Yam 250 OX66. Fishin' & cruisin'

[This message was edited by ocnslr on 12-17-02 at 10:33 PM.]
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Old 12-18-2002, 04:35 AM
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Default NMEA Interface Problem - Thom or someone else to help

The cable from your radar (A & B) are your NMEA interface. Simply put they are data in and data return.
Try your com-1 yellow to A and com-1 orange to B.
If it doesn't work reverse A & B. That should do it.
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Old 12-18-2002, 06:58 AM
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Default NMEA Interface Problem - Thom or someone else to help

I have to tell you, I thought Furuno had the most pizzzzpoor manuals until I just went and read what was on the Si Tex site.

At the very best its confusing as hell, but it looks like you want to do one of two things, and I'll give what seems to me to be the most likely first:

Si Tex Brown to Lowrance Blue
Si Tex Red to Lowrance shield
Do not connect the Red/Shield combinatio to ground.

The other possibility is:
Si Tex Blue to Lowrance Blue
Si Tex Green to Lowrance Red

There is also a third possibility:

Si Tex brown or Blue (either one) to Low' Orange (comm 1) and ST Red or Green to Lowrance green.

I'd try the first set first.

As to the sentences, once again, I am in the dark as to what it is that is really being offered, but it may, and most likely is, the case that you can turn off some, but not all of the output sentences. At any rate, look at the last three letters of the sentences that the radar will accept and to the extent that they are available for output on the Lowrance make sure they are turned on. In particular, and I don't think yo're going to find thise on the optional list, but make sure youre RMA, RMB, possibly RMC, and GLL are all turned on. Those are off the top of my head, so if you want to post the list of possible sentence you can switch let me know what they are and I'll figure out if they are important to you.

Thom

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Old 12-18-2002, 07:57 AM
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Default NMEA Interface Problem - Thom or someone else to help

Red wire for data! Wow, that does not seem right.
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Old 12-18-2002, 09:12 AM
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Default NMEA Interface Problem - Thom or someone else to help

I know what you mean, it (the red wires as a data transfer) sounded all wrong to me. On top of that there is a dire warning on the SiTex's site demanding that you do NOT connect the data negative lines to a ground. It doesn't help a thing that almost everyting concerning Radar interface on the Si Tex site is concerned with connecting to a computer, not to a GPS (although GPS is mentioned).

On that data sentence thing, I think you should know that its really not at all likely that you have to do anything. Its most likely that they are just allowing you to remove sentences that you don't need in order to speed the data transfer process. The way it works is that NMEA talkers send out everything they have in some preset order, and if the listener doesn't need aparticular sentence it just ignores it. Problem is that it still has to wait while the unneeded information is being transfered. That's why you see delays between what is being displayed on a primary machine compared to when it is repeated on another devices screen - some guys complain about it by the way - so the removal just speeds up the processing a very little bit.

Thom

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Old 12-18-2002, 09:27 AM
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Default NMEA Interface Problem - Thom or someone else to help

Thanks for the detailed response, and the effort in looking for an answer. However, I am still confused.
You indicate Si-Tex BROWN in option 1, and Si-Tex BLUE in option 2, but I only have RED and GREEN as the NMEA (A) and (B) wired with the main power connector on the Si-Tex.
Where did you see the BROWN and BLUE for the Si-Tex? Were these with the optional connector plug?

Thanks,
Brian

quote:Originally posted by Thom:
At the very best its confusing as hell, but it looks like you want to do one of two things, and I'll give what seems to me to be the most likely first:

Si Tex Brown to Lowrance Blue
Si Tex Red to Lowrance shield
Do not connect the Red/Shield combinatio to ground.

The other possibility is:
Si Tex Blue to Lowrance Blue
Si Tex Green to Lowrance Red

There is also a third possibility:

Si Tex brown or Blue (either one) to Low' Orange (comm 1) and ST Red or Green to Lowrance green.

I'd try the first set first.

Thom
"For every complex question, there's a simple answer. And it's wrong."
(--H. L. Mencken)

2002 GW Islander 270 - 2001 Yam 250 OX66. Fishin' & cruisin'
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Old 12-18-2002, 12:43 PM
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Default NMEA Interface Problem - Thom or someone else to help

The SiTex site was not specific but it was my impression that it was talking about a second data cable. It really was confusing, that is the best thing I can say about it, In fact it was so bad that I wasn't really sure that It was the same radar that it was talking about. As much as I dislike Lowrance equipment I do have to say that their description was straight forward. If I were you I'd definitly call the Si Tex folks and get it straight from the horses mouth. The one thing that stuck in my mind was the warning not to connect the data negative liine to ground. That, if I was reading it correctly, would rule out connections to common GPS units like those from Garmin.

Thom

"For every complex question, there's a simple answer. And it's wrong."
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Old 12-18-2002, 08:23 PM
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Default NMEA Interface Problem - Thom or someone else to help

Thanks for the inputs from all.
Will try some of the suggestions, and will contact Si-Tex tech support if no joy.

2002 GW Islander 270 - 2001 Yam 250 OX66. Fishin' & cruisin'
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