Is there an NMEA signal on my wires?

Rogershaw said:
Do you have a user friendly terminal emulator running under windows 10 reading a standard RS232 port.
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Various, for checking serial nmea or just text coming in from a serial/usb I use putty sometimes though the arduino IDE is often quicker to open and set, or thonny python ide, fast and easy to use. Or node-red to save the data to a file or send it somewhere else as UDP or TCP.
 
Refueler said:
I am not saying you are wrong ... but when I tried in past to test signal - I have had no indication on any meter digital or other. The NMEA signal itself is so weak that it does not register.

If you are saying RS232 ... then that is a different ball game as that has a definite voltage and has to comply with the No-Damage requirement of the RS232 standards.
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RS232 is nominal swing +12v to -12v but the spec stated min +3 to -3 and max +15 to -15 volt swing.

RS 422/423 and different electrical spec and if I remember NMEA is either RS 422 or RS 423 and is a low impedance design to reduce and interference.

I can remember working on a PDP 12 computer at Hatfield college from stevenage across a 110 baud modem on a teletype. Now I am showing my age.
 
I have a big text book on RS232 somewhere as I used to rewire printers and various for the offices I worked through in Saudi .. years ago. (I've also got a Basic book as well !! Used to write survey routines for inspectors ..... )
The main thing though was that RS232 and other similar standards stipulated that no damage should be possible via the plug socket ... that the units so fitted should survive ...
 
Refueler said:
I am not saying you are wrong ... but when I tried in past to test signal - I have had no indication on any meter digital or other. The NMEA signal itself is so weak that it does not register.

If you are saying RS232 ... then that is a different ball game as that has a definite voltage and has to comply with the No-Damage requirement of the RS232 standards.
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Your experience is interesting. I dont have an explanation for our different results.

Perhaps the update rate on some multimeters is too slow to display the pulse? This seems unlikely given that even cheap multimeters are very capable, but it is a possibility.

I have always seen a signal on a good dgital multimeter over several systems.
The only NMEA 0183 device on our new yacht is a GPS feeding the VHF (the rest is NMEA 2000) and it shows a very nice and distinctive pulse on my multimeter.

Our NMEA 0183 GPS was initially wired up to our 12v converter. it can generate an error code on start up due to a voltage spike and this falure to generate a position is obvious when observing the multimeter.
 
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noelex said:
Your experience is interesting. I dont have an explanation for our different results.

I have always seen a signal on a good dgital multimeter over several systems.
The only NMEA 0183 device on our new yacht is a GPS feeding the VHF (the rest is NMEA 2000) and it shows a very nice and distinctive pulse on my multimeter.

Our NMEA 0183 GPS was initially wired up to our 12v converter. it can generate an error code on start up due to a voltage spike and this falure to generate a position is obvious when observing the multimeter.
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NMEA signal is in the region of mV ....
 
Seeing a RS232 signal on a DVM of AVM depends on a number of factors including speed of transmission, internal resistance and voltage of the output.

The sensitivity of the meter and the reading rate of DVM will also effect the reading .

A LED across the signal to signal ground will show a flash when a signal is transmitted and important if the RS232 pins are reversed it will show this if the receiving side is disconnected because it the signal stops it because the signal is being pulled down due the the impedance of the transmission. send to send connection
 
prv said:
Do you just look for flashes on the RxD LED to see that "something" is happening?

Once it's connected to a PC, dedicated software like Navmonpc might be convenient if you already have it, but it's not necessary just to see if data is being received. NMEA0183 is just text, you can see it in any simple tool that can open the serial port.

Pete
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I use a volt meter, you can just about see the regular pulses as they are squirted out. If they are there then more detailed investigation
 
Refueler said:
Thats on an RS232 ?? on a USB ? ... you do realise that RS232 and USB have a carrier voltage of up to 5V ?
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This is measuring the output on the 0183 signal wires directly from the NMEA 0183 GPS. No USB is invoved or connected.
 
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NMEA0183 correctly is RS-422 electrically with differential pairs although will generally work as RS-232 if common ground on both devices. Standard Horizon and Garmin both use a bastard version with an all-purpose ground, so more like RS-232.
Lots of answers to OP but without PC or similar on board, the radio itself is probably best indicator. Check the wiring connections, especially ground wire. Is it all secure? Those thin wires can break inside.
How do you know GPS receiver is alive? Does it have an indicator LED? Is it flashing when it should?
If you have a chart plotter, it may have an NMEA diagnostic screen where you can see received data. Hookup the GPS receiver to check output.
 
Beneteau381 said:
I use a volt meter, you can just about see the regular pulses as they are squirted out. If they are there then more detailed investigation
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This has also always been my experience with NMEA 0183.

The voltage pulse indicates a signal is present. This eliminates many problems, so it is a valuable troubleshooting tool.

It does not show if the signal is a valid NMEA sentence. Therefore it does not rule out all problems, but generally a defective device will not generate a signal so any voltage on the signal wires will be constant.
 
Refueler said:
NMEA signal is in the region of mV ....
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From section 3.5.3 of the NMEA0183 standard version 4.10 which uses voltage levels based on RS422...
The receive circuit shall be designed for operation with a minimum differential input voltage of 2.0 Volts
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and from section 3.5.5...
all receive circuit devices should be capable of withstanding 15 volts between signal lines "A" and "B"
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and for the earlier standards where NMEA0183 was based on RS232...
For reasons of compatibility with equipment designed to earlier versions of this standard, it is noted that the "idle, marking, logical "1", OFF or stop bit state" had previously been defined to be in the range -15 to + 0.5 Volts. The "active, spacing, logical "0", ON or start bit state" was defined to be in the range +4.0 to +15 Volts.
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noelex said:
This has also always been my experience with NMEA 0183.

The voltage pulse indicates a signal is present. This eliminates many problems, so it is a valuable troubleshooting tool.

It does not show if the signal is a valid NMEA sentence. Therefore it does not rule out all problems, but generally a defective device will not generate a signal so any voltage on the signal wires will be constant.
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Yes. That does work for either old standard NMEA0183 with signal and ground or new standard with A/B.
 
Refueler said:
There must be a carrier and ground ...
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That is not true. Later versions of NMEA0183 are not carrier and ground (i.e. single ended), they specify differential (signal + and signal -) called A and B in NMEA0183. In version 4.10 of the standard it explicitly bans a direct connection between either signal and ground...

Within a LISTENER there shall be no direct electrical connection between the signal line, "A", return line, "B", or shield and ship's ground or power. Isolation from ship's ground is required.
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AngusMcDoon said:
That is not true. Later versions of NMEA0183 are not carrier and ground (i.e. single ended), they specify differential (signal + and signal -) called A and B in NMEA0183. In version 4.10 of the standard it explicitly bans a direct connection between either signal and ground...
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Who said connecting signal and ground ???? Do that and kiss item goodbye.

When you connect up your RS232 .... NMEA ..... whatever GPS Puck etc. - the power -ve provides that 'ground' necessary to have not only power circuit - but also the data signal circuit.

I have a bag containing latest GPS unit and associated power BEC ready to install to my VHF to not have to have all the leads from my GPS plotter .... guess what ...... "the power -ve provides that 'ground' necessary to have not only power circuit - but also the data signal circuit."

No-one is talking about extra connection ...

Why not check this out ... my new GPS unit ...

Beitian Smallest Mini Dual GLONASS+GPS BN-180 Micro Double GPS Antenna Module UART TTL For CC3D F3 RC Drone Airplane RC Parts from Toys Hobbies and Robot on banggood.com
 
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