RS-232 or RS-422?

[bewitched]

I have to replace my GPS antenna. I am looking to hook it up via the NMEA in port on the course computer (Autohelm Type 300).

NMEA GPS units seem to output either RS-232 or RS-422. Which one do I need?

and how do I wire it? (Autohelm has inputs for NMEA + and NMEA - )

RS-232 wiring info below:

Violet NC/1PPS
Red VCC, Power Supply ( VDC 9V-34V)
Brown NC
Green RS-232 Transmit Tx, Output Signal
Blue NC
White RS-232 Receiver Rx, Input Signal
Black Ground
Gray Shield Wire, Signal Ground

[s/v Jedi]

Mostly, when your inputs are labeled like NMEA+ and NMEA- you have a double-ended RS422 interface. When you see something like Tx and COM(mon) where COM is the same as the 12V DC negative, you have single ended RS232.

Almost everyone just takes it for granted that connecting 422 to 232 works, but it's more accidental than wisdom. The other way around causes trouble often. So, you better get both sides as the same interface type, with RS422 the preferred and official NMEA-183 one.

those color-codes of wiring are indeed RS232 single ended because both transmit and receive have only one wire and share the "black ground" as the 2nd one.

cheers,
Nick.

[Talbot]

I found the easiest way was to connect the GPS to a standard serial connector, and then use a serial to USB converter to input to the computer

[scotte]

Your AutoHelm A/P is definitely differential, but whether or not the GPS is depends on what the GPS is...

[fairbank56]

Just because it's labeled (+) and (-), does not mean it carries differential signals. Marine electronic's manufacturer's very commonly use this convention to label their NMEA wiring in their installation installation instructions when in fact the input/output's are single ended. Generally as far as NMEA devices go, a differential output will drive a single ended input but is left often the case the other way around. Converter devices are readily available if needed and for us techie's, are easily constructed from a minimum of components.

Eric

[s/v Jedi]

Originally Posted by Talbot

I found the easiest way was to connect the GPS to a standard serial connector, and then use a serial to USB converter to input to the computer

Talbot,

I would like to disagree with you ;-) The easiest way is to use a NMEA0183 to USB converter, like this one: ShipModul Marine Electronics

However, that will set you back $180 and if you only use one input port (out of the three) it is cheaper to use a RS232 to USB converter. I would personally go for a Shipmodul mux when I connect two or three inputs, like GPS + AIS or GPS + AIS + compass/instruments.

The mux I linked to above does support a high-speed 38k4 link from an AIS receiver/transponder.

cheers,
Nick.

[Talbot]

Originally Posted by s/v Jedi

Talbot, I would like to disagree with you ;-) The easiest way is to use a NMEA0183 to USB converter, like this one: ShipModul Marine Electronics.

I never mind people disagreeing with me especially when they are wrong

However, there are always many different ways of solving a problem. I preferred to bring the AIS data in on a seperate USB, and to tap off the GPS feed before connecting it to a serial connector, so that I had the GPS feed for the DSC radio. I was then able to feed the GPS signal in separately. The software I was using was able to cope with the two leads at separate data rates, and I had avoided your expensive mux.

[s/v Jedi]

Originally Posted by Talbot

I never mind people disagreeing with me especially when they are wrong
[...]
and I had avoided your expensive mux.

Exactly, your setup is cheaper. But soldering a DB-9 and splicing for VHF is certainly not easier than the mux way where you just pop the wires into the mux!

Don't confuse cheap with easy...
Also, you better get a good serial to USB converter like the Keyspan because when you get into those "windhose detects GPS as mouse" problems cheap becomes a nightmare ;-)

ciao!
Nick.

[W32PAMELA]

Many small form factor computers with multiple COM ports will have at least 1 port that is either jumper or BIOS selectable as an RS232 or an RS422 port along with the ability to provide 5v or 12v output on pin 9 to power equipment such as a GPS. Most Nav programs provide software multiplexing of multiple serial inputs with multiple baud rates.

[Pblais]

Don't confuse cheap with easy...
Also, you better get a good serial to USB converter like the Keyspan because when you get into those "windhose detects GPS as mouse" problems cheap becomes a nightmare ;-)

Windows almost always detects a GPS as a Mouse and screws you. WAIT to connect the GPS until after the Windows session boots and only then power ON the GPS. If it is already wired up then don't power it on until after Windows boots. If and you see the desktop and it's ready. The serial protocol is NOT standard across hardware. The RS-232C standard has enough holes to drive a truck through it. It's no wonder it's been dead for a good long time now. 30 years ago it was a PITA when I first started.

I like the pfranc USB converters just fine. They even have idiot lights for transmit / receive signals. Anyone familiar with a breakout box knows.

[Paul Elliott]

Originally Posted by Pblais

Windows almost always detects a GPS as a Mouse and screws you. WAIT to connect the GPS until after the Windows session boots and only then power ON the GPS. If it is already wired up then don't power it on until after Windows boots.

Here are three fixes for the "Spurious Serial Mouse Detection" problem:


(Taken from this blog: Welcome to BMW World. My world. » Blog Archive » Serial device (GPS, I-Bus adapter, etc) detected as serial mouse on Windows XP - solutions)
----------------
Solution 1 - disable serial mouse in Device Manager
Boot Windows XP as usual. Windows installs the serial mouse driver and the cursor gets crazy. After the system finishes booting, unplug the serial device. The mouse cursor should return to normal. Open Device Manager (Start / Control Panel / System / Hardware / Device manager), expand the branch labeled ‘Mice and other pointing devices’ and there you will find the false serial mouse. Do not uninstall it, as it will be detected again upon restart. Simply disable it. Windows will remember not to use that device again.
Plug back the serial device and restart Windows.

Solution 2 - edit boot.ini file
Open boot.ini with your favorite text editor (it should be in the root of your C: drive, sometimes hidden as it is a system file). Find a line similar to multi(0)disk(0)rdisk(0)partition(1)\WINDOWS=”Micro soft Windows XP Professional” and add /fastdetect to the end of the line. This should turn off serial mouse detection on all com ports. You can also use /fastdetect:comx (where x=actual com number) to disable detection on specific com port. You can find the details here. Note that various workarounds on the web suggest using /NoSerialMouse or /NOSERIALMICE instead. This switches will not work as they were created for Windows NT / 2000 and are not allowed in Windows XP.
Save the modified boot.ini file and reboot.

Solution 3 - Microsoft COMDIsable tool
Apparently the 2 solutions above do not work in 100% cases, so the guys at MS have come with their own solution, called COMDisable. It’s a small application designed for Windows Server 2003, Windows XP and Windows 2000 Service Pack 3 (SP3) or later that allow you to turn off serial mouse detection via command line.
comdisable /list will list all available com ports with their status
comdisable /disable COMPortNumber or comdisable /enable COMPortNumber will disable/enable a specific com port you select.
After running the command, simply restart the PC.
----------------

I have used solutions #1 and #2 successfully. #3 sounds good, but I haven't tried it.

[bewitched]

I'm not sure if I understand half of the above threads..........

My problem is that after a less than textbook spinaker drop I am now sans gps antenna. Rather than buying the expensive Raymarine and connecting to the seatalk network, I have opted for the significantly cheaper NMEA output antenna to be connected to the NMEA in on my course computer (not laptop - Autohelm 300).

I seem to have two choices here. 232 or 422 (talking about the signal here - not the type of connector). Judging by Jedi's first post I should be buying the 422. The wiring for which is:

Violet NC/1PPS
Red VCC, Power Supply ( VDC 9V-34V)
Brown RS-422 Transmit Tx - , Output Signal
Green RS-422 Transmit Tx+, Output Signal
Blue RS-422 Receiver Rx -, Input Signal
White RS-422 Receiver Rx + , Input Signal
Black Power Ground
Gray Shield Wire, Signal Ground

So presumably I should be hooking up the Brown & Green to the NMEA + and - on the course computer??

Correct??

[scotte]

The OP never mentioned linking in a computer or AIS as far as I can tell, how did this get so off topic? *SIGH*

[s/v Jedi]

Bewitched,

The brown and green are the data GPS->course computer. You also need to connect the red & black to supply power to the GPS, plus the "gray" shield wire.

Now listen here: I don't know which GPS this is nor what it's default settings are. But if you ever need to change things inside the GPS sensor, you will need the blue and white wires too. Make sure you buy something that works out of the box without needing to change settings because that will be a frustrating experience.

cheers,
Nick.

[bewitched]

The product is an Evermore 920 smart antenna

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