Instruments can't see NMEA 0183 data from Ublox Neo-6M GPS module

[Elbows]

Hello All,

Not sure whether anybody can help with this, but there are some very knowledgeable people here so it's worth an ask.

I've bought a Ublox Neo-6M based GPS module to supply position data to a Standard Horizon GX1500E DSC VHF and a Nasa AIS "Radar" display. Both require NMEA 0183 at 4800 baud. The AIS specifies RMC sentences amd I'm assuming the VHF will also be satisfied with RMC sentences.

I'm using u-center which is a very nice piece of free Windows software which Ublox provide for monitoring and setting up their GPS modules. The module has a 5 pin serial connection - Vcc, Gnd, Tx, Rx and PPS (which isn't used for this application). As instructed I've connected the GPS module to the PC via a serial-to-USB adaptor and it works perfectly. It gets a fix within a few seconds even indoors and displays the data in u-center.

U-center has many arcane options involving hundreds of 3-letter acronyms that mean nothing to me, however I think I've decyphered all the relevant ones which allow me to set up the module to transmit the basic data I need. I've been able to set the baud rate to 4800, I've got it outputting valid NMEA GPRMC sentences and turned off the other default outputs. I've enabled UART for the modules port and set the output to NMEA. All these settings have been permanently saved to the module and according to u-center's displays it's behaving just as I want it to.

However when I connect it to the VHF and/or the AIS they aren't receiving any data.

The AIS has a single wire to receive GPS data which I've connected to the module's Tx pin. I understand that in such cases the power supply ground is used as the negative data connection. To power the module I've used a 12V-to-5V DC-DC converter which has a common ground with the instrument's 12V power supply. I've also tried adding a direct connection between the grounds just in case something weird was happening. The AIS just sits there waiting for GPS data.

The VHF installation diagram shows positive amd negative connections to the GPS output so I've connected the positive to the module's Tx and the negative to ground. It just says "No time, no postion data" when turned on.

I suspect I need to do something else to the module setup in u-center but I can't see anything else which could be relevant. I've emailed Ublox and Waveshare (the module manufacturer) but neither have replied. Any suggestions for what I should be looking for?

Thanks.

 

[matthewriches]

Screenshot of the data you have coming out?

 

[MikeCC]

Are you sure it's connected to Tx not Rx (or another pin)?

Supply voltage is given as 2.7-3.7V so that might be an issue.

 

[GregOddity]

Hello All,

Not sure whether anybody can help with this, but there are some very knowledgeable people here so it's worth an ask.

I've bought a Ublox Neo-6M based GPS module to supply position data to a Standard Horizon GX1500E DSC VHF and a Nasa AIS "Radar" display. Both require NMEA 0183 at 4800 baud. The AIS specifies RMC sentences amd I'm assuming the VHF will also be satisfied with RMC sentences.

I'm using u-center which is a very nice piece of free Windows software which Ublox provide for monitoring and setting up their GPS modules. The module has a 5 pin serial connection - Vcc, Gnd, Tx, Rx and PPS (which isn't used for this application). As instructed I've connected the GPS module to the PC via a serial-to-USB adaptor and it works perfectly. It gets a fix within a few seconds even indoors and displays the data in u-center.

U-center has many arcane options involving hundreds of 3-letter acronyms that mean nothing to me, however I think I've decyphered all the relevant ones which allow me to set up the module to transmit the basic data I need. I've been able to set the baud rate to 4800, I've got it outputting valid NMEA GPRMC sentences and turned off the other default outputs. I've enabled UART for the modules port and set the output to NMEA. All these settings have been permanently saved to the module and according to u-center's displays it's behaving just as I want it to.

However when I connect it to the VHF and/or the AIS they aren't receiving any data.

The AIS has a single wire to receive GPS data which I've connected to the module's Tx pin. I understand that in such cases the power supply ground is used as the negative data connection. To power the module I've used a 12V-to-5V DC-DC converter which has a common ground with the instrument's 12V power supply. I've also tried adding a direct connection between the grounds just in case something weird was happening. The AIS just sits there waiting for GPS data.

The VHF installation diagram shows positive amd negative connections to the GPS output so I've connected the positive to the module's Tx and the negative to ground. It just says "No time, no postion data" when turned on.

I suspect I need to do something else to the module setup in u-center but I can't see anything else which could be relevant. I've emailed Ublox and Waveshare (the module manufacturer) but neither have replied. Any suggestions for what I should be looking for?

Thanks.

Hard without a screenshot. Did you measure the voltage as you connect it? Some wiring WILL give you problems that are hard to diagnose, I have that issue with RTS GPS ( real time Systems) installs for Emergency vehicles, some of the wiring supplied is not of adequate quality in my case and I lose 1.2 volts on a 3m length of wiring and I get exactly no position no data. New wiring and voila in my case.
But it is hard with u-center sometimes.
Can you post a few screenies?

 

[Elbows]

Thanks for all the replies.

Screenshot of the data you have coming out?

See below. Let me know if more would help.

Are you sure it's connected to Tx not Rx (or another pin)?

Good thought, but yes, definitely connected to Tx. I triple checked all the connections after an earlier brainfart with the serial-to-USB adaptor when I connected Tx to TX and Rx to Rx and wondered why the module didn't work in u-center!

Supply voltage is given as 2.7-3.7V so that might be an issue.

That's the supply voltage range for the Ublox chip/module. The GPS unit itself is a small PCB with the Ublox module, ancilliary conponents and antenna mounted on it. The GPS unit's supply voltage spec is 3.3V/5V. I assume it's got an onboard voltage regulator so that it can be set up as a native USB unit if required. My serial-to-USB adaptor has pins for 5V Vcc and 3.3V and the module works perfectly in u-center when connected to either.

Hard without a screenshot. Did you measure the voltage as you connect it? Some wiring WILL give you problems that are hard to diagnose, I have that issue with RTS GPS ( real time Systems) installs for Emergency vehicles, some of the wiring supplied is not of adequate quality in my case and I lose 1.2 volts on a 3m length of wiring and I get exactly no position no data. New wiring and voila in my case.
But it is hard with u-center sometimes.
Can you post a few screenies?

At the moment I've got everything on my desk with a mains powered 12v 5A brick supplying the instruments and the 5V DC-DC converter. Both the 12V and the 5V are spot on and rock steady. All the wires are short and there are no other loads connected. Could ripple on the 12V confuse the instruments?

 

[rogerthebodger]

Have you set up CFG-COM0 and CFG-COM1 pins 14 and 15 on the NEO-6 to give the correct Baud rate output.

Page 11 and 12 in the data sheet.

https://www.u-blox.com/sites/default/files/products/documents/NEO-6_DataSheet_(GPS.G6-HW-09005).pdf

 

[Elbows]

Have you set up CFG-COM0 and CFG-COM1 pins 14 and 15 on the NEO-6 to give the correct Baud rate output.

Page 11 and 12 in the data sheet.

https://www.u-blox.com/sites/default/files/products/documents/NEO-6_DataSheet_(GPS.G6-HW-09005).pdf

I'm just using u-center for setup, I haven't made any hardware mods and I don't think I need to.

From the datasheet:

"NEO-6 modules provide configuration pins for boot-time configuration. These become effective immediately after start-up. Once the module has started, the configuration settings can be modified with UBX configuration messages. The modified settings remain effective until power-down or reset. If these settings have been stored in battery-backup RAM, then the modified configuration will be retained, as long as the backup battery supply is not interrupted"

So it'll boot at 9600 baud (default) but because I've saved the 4800 baud setting it'll immediately change to 4800 baud. This is confirmed by the fact that when unplug it and then reconnect it retains all my settings in u-center including the 4800 baud rate.

 

[earlybird]

Just a thought, the GPS module seems to be a very low voltage device. Are you confident that it is providing sufficient voltage swing on the NMEA output to drive the listeners?
If it's marginal, would temporary disconnection of one make any difference?

 

[Elbows]

Just a thought, the GPS module seems to be a very low voltage device. Are you confident that it is providing sufficient voltage swing on the NMEA output to drive the listeners?
If it's marginal, would temporary disconnection of one make any difference?

Good thought. The voltage level did cross my mind, but standard NMEA 0183 is one of the outputs it's designed to transmit so I'd be very surprised if that hadn't been taken into account. The module's Vcc is 3.3V/5V but I'm assuming that there's some sort of voltage boost for NMEA output. I'll take another look at the datasheet to see if it gives the NMEA output specs. At the moment I'm testing the instruments one at time anyway.

 

[Elbows]

Just a thought, the GPS module seems to be a very low voltage device. Are you confident that it is providing sufficient voltage swing on the NMEA output to drive the listeners?

According to the Neo-6 datasheet: "Digital IO Pin High level output voltage Voh All VCC -0.4 V Ioh=4mA" - so unless there's a signal amplifier on the PCB the output voltage will 4.6V when using 5V Vcc.

After a spot of digging around I get the impression this should be sufficient. People successfully use Garmin handheld GPS units to drive instruments and they've only got a couple of AAs inside. I haven't been able to find any hard and fast specs for NMEA signal voltage levels, there seems to be a lot of vagueness.

 

[laika]

The voltage level did cross my mind, but standard NMEA 0183 is one of the outputs it's designed to transmit so I'd be very surprised if that hadn't been taken into account.

Are they perhaps talking about data format rather than the electrical spec? If it's outputting 3.3v ttl that may not be what you need.

 

[Elbows]

Are they perhaps talking about data format rather than the electrical spec? If it's outputting 3.3v ttl that may not be what you need.

You could be right. It should be outputting 4.6V minimum as I'm using 5V Vcc, but I'm having a hard job finding out whether that's sufficient.

 

[Elbows]

I'm no electronics wizard but I have do have some basic knowledge and skills and I could knock up a simple amplifier if I knew what was needed. Would it be good enough to just make a simple amplifier using a single transistor and appropriate resistors? I assume we're not talking about high frequency signalling with it's associated issues here.

 

[Elbows]

You could be right. It should be outputting 4.6V minimum as I'm using 5V Vcc, but I'm having a hard job finding out whether that's sufficient.

I'm wrong there, it's going to 2.9V because it's 3.3V Vcc for the IC. 5V is the Vcc of the GPS unit.

 

[GregOddity]

I'm wrong there, it's going to 2.9V because it's 3.3V Vcc for the IC. 5V is the Vcc of the GPS unit.

you going to need to measure it. Trust me on this one, if you lose over 0.3 volts you end up here asking for help. did you try changing the wiring? Always start by the basics. I always go for the wiring and connection’s before even thinking of digging up my Oscilloscope or even bothering with the software. As soon as you connect the unit you should have some sort of life out of it. It appears you have nothing.
Recheck all the wiring and retighten every screw.

 

[Elbows]

you going to need to measure it. Trust me on this one, if you lose over 0.3 volts you end up here asking for help. did you try changing the wiring? Always start by the basics. I always go for the wiring and connection’s before even thinking of digging up my Oscilloscope or even bothering with the software. As soon as you connect the unit you should have some sort of life out of it. It appears you have nothing.
Recheck all the wiring and retighten every screw.

As I said, it's all sitting on my desk with good connections, short wires and no other loads. It's not on the boat. I don't have an oscilloscope so I can't measure the signal high level, but the datasheet for the module says 2.9V. As you seem to know about this stuff, is that high enough?

If I hadn't bothered with the software it would be transmitting at the wrong baud rate so it would be a waste of time connecting it. Because I've set it up in the software I know that it is outputting the correct data at the correct baud rate. What I don't know is why my instruments aren't seeing that data. It might be some other setting in the software that I've missed, or it might be transmitting with the wrong electrical characteristics. It's definitely not the quality of the connections, I've checked.

 

[GregOddity]

As I said, it's all sitting on my desk with good connections, short wires and no other loads. It's not on the boat. I don't have an oscilloscope so I can't measure the signal high level, but the datasheet for the module says 2.9V. As you seem to know about this stuff, is that high enough?

If I hadn't bothered with the software it would be transmitting at the wrong baud rate so it would be a waste of time connecting it. Because I've set it up in the software I know that it is outputting the correct data at the correct baud rate. What I don't know is why my instruments aren't seeing that data. It might be some other setting in the software that I've missed, or it might be transmitting with the wrong electrical characteristics. It's definitely not the quality of the connections, I've checked.

I'm gonna go out on a limb here and say that you actually need 3.3 v. Can you make a pic of the all thing and post it so I can see what you got?

 

[Elbows]

I'm gonna go out on a limb here and say that you actually need 3.3 v. Can you make a pic of the all thing and post it so I can see what you got?

A picture won't tell you anything you don't already know. The connections are very simple and I've described them in my original post.

What makes you think that 3.3V is the magic number?

 

[GregOddity]

A picture won't tell you anything you don't already know. The connections are very simple and I've described them in my original post.

What makes you think that 3.3V is the magic number?

Most of the setups I built need a minimum of 3,3v albeit using diff components than you. Some will not even work with less the the 5v , the 2.9 is too low, but having said that is hard to see what you got going and how you got it set up.

 

[duncan99210]

No expert on this topic but this document from Actisense http://www.actisense.com/wp-content/uploads/2017/07/NMEA-0183-Information-sheet-issue-4-1-1.pdf states that the minimum voltage that most listeners are looking for is 5v. So if the output is less than 5v it may be being recognised by the computer but be too low to be read by the ais or radio, especially as the voltage will be further dropped by trying to feed both of them.