NMEA multiplexer

[Boathook]

My gps will not supply data to more than one instrument and I have told that I require a multiplexer to boost the signal to the other instruments to use as repeaters, etc. The muliplexers I have seen so far (cost £££), all seem to combine various outputs rather than boost a signal. Does anyone else have this problem and how was it sorted. The cheaper the better at present !!

 

[rob2]

Just checking the obvious, particularly as you didn't say what the GPS unit is. The standard is that a NMEA output should be able to feed up to four listeners - have you actually tried more than one? What are the units you are trying to feed into?

On my boat, the GPS NMEA is fed into the VHF and into a Raymarine repeater, which then chains the info throughout the instrument system, including the autohelm using Raytalk. I also have a switched line of NMEA direct to the autohelm as built in redundancy.

I've seen multiplexers and can't imagine why they cost so much for doing precious little - perhaps you could beg a YAPP to sort this out?

Rob.

 

[prv]

Are you sure that the GPS will not supply more than one? You can connect multiple listeners to the same pair of wires, they don't each need their own port. I guess at some point the talker will run out of power to properly trigger all the listeners, but that should be loads and loads, not three or four. I've never heard of a talker so feeble that it can only supply one listener, which is why you can't find a box to remedy this.

What GPS is it?

Pete

 

[nimbusgb]

If you just want to boost the NMEA signal it can be done with very little effort. A pair of chips, one receiver, one transmitter and a power supply regulator will do it. probably got most of the components lying around in a bits drawer. Cost < £10

What GPS though? I'd be surprised if there is not something else afoot.

 

[pvb]

My gps will not supply data to more than one instrument and I have told that I require a multiplexer to boost the signal to the other instruments to use as repeaters, etc. The muliplexers I have seen so far (cost £££), all seem to combine various outputs rather than boost a signal. Does anyone else have this problem and how was it sorted. The cheaper the better at present !!

The advice to buy a multiplexer is wrong; if you have to get anything, it would something like an Actisense buffer, which amplifies the NMEA signal. However, your GPS should certainly drive more than one instrument. As buffers typically cost £150ish, it'd be cheaper to get a new GPS.

 

[Boathook]

GPS is a Furuno GP-31. Other instruments are a Furuno 1623 radar & NX300 navtex and a ICOM M423 radio. I have always found that the GPS would only supply one instrument to use as a repeater but having fitted the DSC radio this is now a problem. It has been suggested to daisy chain the instruments but this is easier said than done and there are enough wires without adding more !

 

[earlybird]

I have a Furuno GP32. It feeds a 1623 radar, an Icom 505 DSC radio and a Yeoman, plus an autohelm instrument / tillerpilot system, including a repeater, no problem.
IIRC, I previously connected the Navtex to it as well, but this gives no benefit IMHO.
Daisy-chaining isn't correct, the listeners should be in parallel.

 

[AngusMcDoon]

If all you are interested in is basic GPS data (i.e. not routes) then the easiest way is to buy a serial GPS mouse and a 12V to 5V power supply. Ebay Globalsat BR-355.

 

[AngusMcDoon]

If you just want to boost the NMEA signal it can be done with very little effort. A pair of chips, one receiver, one transmitter and a power supply regulator will do it. probably got most of the components lying around in a bits drawer. Cost < £10.

NMEA spec says that listeners have to be able to accept RS-232...

Cost: about 67p.

Just noticed I've got my IN and OUT the wrong way round.

 

[Boathook]

I have a Furuno GP32. It feeds a 1623 radar, an Icom 505 DSC radio and a Yeoman, plus an autohelm instrument / tillerpilot system, including a repeater, no problem.
IIRC, I previously connected the Navtex to it as well, but this gives no benefit IMHO.
Daisy-chaining isn't correct, the listeners should be in parallel.

PM sent.

 

[lw395]

There is some merit in opto-isolating the data, if the devices are fed by separate breakers or you want to supply the GPS from an emergency battery. Does not cost much!

 

[nimbusgb]

NMEA spec says that listeners have to be able to accept RS-232...

Cost: about 67p.

Just noticed I've got my IN and OUT the wrong way round.

It Does? it may have in NMEA option 1 but after that it became 0/5v differential spec.

two 75176's back to back is a much more elegant solution iyam and at 0.55 each cheaper too if you include the cost of your 5 1uf caps at 0.20 each.

http://www.actisense.com/Downloads/TechTalk/NMEA 0183/The NMEA 0183 Information Sheet.pdf

 

[AngusMcDoon]

It Does? it may have in NMEA option 1 but after that it became 0/5v differential spec.

From the NMEA FAQ...

The NMEA-0180 and 0182 standards say that the talker output may
be RS-232...

NMEA-0183 accepts this, but recommends that the talker output
comply with EIA-422...

I read the above that NMEA devices should be able to accept EIA-232, but I may be wrong. I'd agree though that it's a bit of a clanky way of doing it.

 

[lw395]

From the NMEA FAQ...



I read the above that NMEA devices should be able to accept EIA-232, but I may be wrong. I'd agree though that it's a bit of a clanky way of doing it.

The world of marine electronics likes 'clanky'.

 

[prv]

There is some merit in opto-isolating the data, if the devices are fed by separate breakers or you want to supply the GPS from an emergency battery. Does not cost much!

Sounds like there are far greater experts than me here, but I always understood that opto-isolated inputs was a requirement of "proper" NMEA?

Pete