2021-07-06, 09:49 PM
(This post was last modified: 2021-07-06, 10:02 PM by burgoynebc@netscape.net.)
Hi Kever:
I have had the same issues:
I have installed a neo 6m GPS module to replace a globalsat GPS puck type GPS antenna. This has been in usage for years. This has been with the intent to eliminate some issues with using a USB interface with my tablet chartplotte (windows). and also to allow a GPS signal to be fed into my new Uniden VHS.
I have valid nmea 0183 sentences being received into my tablet via a usb to ttl adapter, and in parallel to an arduino MCU used for autopilot. Both these "listeners" are fully functional. This working circuit is TTL positive 5v - 2 wire.
However I have had absolutely no success in getting my VHS to see the same NMEA input.
My next trip to the boat I will try totally removing the green wire and ground wires and measure the signal both connected and disconnected.
I phoned to get support from Uniden and basically they were unable to give any other info other than what is printed in their manual (confusing due to lack of sufficient content)
I have researched on line re nmea electrical specifications. In overview NMEA is a pretty mixed up scene whereby the various revisions are incompatible, and so devices that were designed for different nmea revisions will not work with one another adaquately. For instance a version less than version 2 (my Uniden Manual says " in compliance with" version 2) uses a 2 wire data system = data and ground. The VHF uses per nmea version 2, a 4 wire system = data in plus and neg, and data out plus and neg, with the neg not being neccesariliy the same, or common, with ground or shield. It is totally unclear to me what the VHF expects to see re data volts. It is very clear that most manufacturers do not adhere to the "standard" for instance regarding whether or not the signal goes negative on the start or stop bit etc (at this point it gets over my pay grade!!). For sure my working circuit is TTL positive 5v /0v (TX/RX) while the VHF ( if indeed it is designed as fully version 2) is pos and neg with regard to each of the in/out pairs and each pair is ungrounded. But what does the RPI need to see? I'm not so sure about this as USB is 4 wire - but with power -/+ and data +/- and is a different protocol. With the rs 485 adapter you are, I think, taking the TTL data (albeit version 2 spec) and converting it to USB. The VHF is expecting the raw signal and the RPI in getting the data signal via adapter does not indicate that the data the VHF sees is indeed valid for its purposes.
I too am trying to get a RPI 4 into my system and am have some substantial issues in getting the serial/AIS configuarations set up properly.
Since you are using a RS 485 interface adapter you are somewhat ahead of me in its usage. I was hoping to use the RPI pins rather than USB. Looking at some of the rs 485 adapters on ebay, it would be good to know which type adapter you have - some seem to be 2 wire while others look like 4 wire.
I had put my RPI aside after getting pretty fraustrated with these issues, but in writing this reply it bring me to look towards abandoning my plan to use the RPI pins and getting some rs 485 adapters . This will not help in getting the VHF to connect.
It would be good to make contact and share any knowledge improvements.
Richard
SV Zolanda
heres a suplement to my previous - see
https://www.bb-elec.com/Learning-Center/...ndard.aspx
An extract re volts
"
The EIA RS-485 Specification labels the data wires "A" and "B", but many manufacturers label their wires "+" and "-". In our experience, the "-" wire should be connected to the "A" line, and the "+" wire to the "B" line. Reversing the polarity will not damage a 485 device, but it will not communicate. This said, the rest is easy: always connect A to A and B to B. Signal ground, don't forget it. While a differential signal does not require a signal ground to communicate, the ground wire serves an important purpose. Over a distance of hundreds or thousands of feet there can be very significant differences in the voltage level of "ground." RS-485 networks can typically maintain correct data with a difference of -7 to +12 Volts.
"
NMEA 0183 version 2 specs 5v and remember RPI is a 3.3v device
Richard
I have had the same issues:
I have installed a neo 6m GPS module to replace a globalsat GPS puck type GPS antenna. This has been in usage for years. This has been with the intent to eliminate some issues with using a USB interface with my tablet chartplotte (windows). and also to allow a GPS signal to be fed into my new Uniden VHS.
I have valid nmea 0183 sentences being received into my tablet via a usb to ttl adapter, and in parallel to an arduino MCU used for autopilot. Both these "listeners" are fully functional. This working circuit is TTL positive 5v - 2 wire.
However I have had absolutely no success in getting my VHS to see the same NMEA input.
My next trip to the boat I will try totally removing the green wire and ground wires and measure the signal both connected and disconnected.
I phoned to get support from Uniden and basically they were unable to give any other info other than what is printed in their manual (confusing due to lack of sufficient content)
I have researched on line re nmea electrical specifications. In overview NMEA is a pretty mixed up scene whereby the various revisions are incompatible, and so devices that were designed for different nmea revisions will not work with one another adaquately. For instance a version less than version 2 (my Uniden Manual says " in compliance with" version 2) uses a 2 wire data system = data and ground. The VHF uses per nmea version 2, a 4 wire system = data in plus and neg, and data out plus and neg, with the neg not being neccesariliy the same, or common, with ground or shield. It is totally unclear to me what the VHF expects to see re data volts. It is very clear that most manufacturers do not adhere to the "standard" for instance regarding whether or not the signal goes negative on the start or stop bit etc (at this point it gets over my pay grade!!). For sure my working circuit is TTL positive 5v /0v (TX/RX) while the VHF ( if indeed it is designed as fully version 2) is pos and neg with regard to each of the in/out pairs and each pair is ungrounded. But what does the RPI need to see? I'm not so sure about this as USB is 4 wire - but with power -/+ and data +/- and is a different protocol. With the rs 485 adapter you are, I think, taking the TTL data (albeit version 2 spec) and converting it to USB. The VHF is expecting the raw signal and the RPI in getting the data signal via adapter does not indicate that the data the VHF sees is indeed valid for its purposes.
I too am trying to get a RPI 4 into my system and am have some substantial issues in getting the serial/AIS configuarations set up properly.
Since you are using a RS 485 interface adapter you are somewhat ahead of me in its usage. I was hoping to use the RPI pins rather than USB. Looking at some of the rs 485 adapters on ebay, it would be good to know which type adapter you have - some seem to be 2 wire while others look like 4 wire.
I had put my RPI aside after getting pretty fraustrated with these issues, but in writing this reply it bring me to look towards abandoning my plan to use the RPI pins and getting some rs 485 adapters . This will not help in getting the VHF to connect.
It would be good to make contact and share any knowledge improvements.
Richard
SV Zolanda
heres a suplement to my previous - see
https://www.bb-elec.com/Learning-Center/...ndard.aspx
An extract re volts
"
The EIA RS-485 Specification labels the data wires "A" and "B", but many manufacturers label their wires "+" and "-". In our experience, the "-" wire should be connected to the "A" line, and the "+" wire to the "B" line. Reversing the polarity will not damage a 485 device, but it will not communicate. This said, the rest is easy: always connect A to A and B to B. Signal ground, don't forget it. While a differential signal does not require a signal ground to communicate, the ground wire serves an important purpose. Over a distance of hundreds or thousands of feet there can be very significant differences in the voltage level of "ground." RS-485 networks can typically maintain correct data with a difference of -7 to +12 Volts.
"
NMEA 0183 version 2 specs 5v and remember RPI is a 3.3v device
Richard