GPS for Icom radios

[flyingnut40]

Interesting, given that NMEA 0183 is optically isolated, where the voltage concern is eludes me......
And yes, the ICOM radio is looking for a NMEA 0183 data stream I believe at TTL levels and there is no way to accommodate a USB driver.....

[CarinaPDX]

Originally Posted by flyingnut40

Interesting, given that NMEA 0183 is optically isolated, where the voltage concern is eludes me...

NMEA 0183 v2+ is supposed to be differential too, but there is a lot of equipment out there that isn't differential and doesn't have opto-isolators in them. Many, but not all, ICs used for RS-232 work for both 12V and 5V - it all depends on the threshold used. A 7V threshold is not going to work with 5V signals, but a 3V will.

In the real world I suspect that very few GPS receivers have opto-isolation. Marine devices with NMEA certification almost certainly do, as that is the spec. Considering the cost to join the NMEA club, buy the specs, and get products certified, it is understandable that there are a lot of "NMEA compatible" products out there that interoperate but don't meet the spec.

Greg

[flyingnut40]

Originally Posted by CarinaPDX

NMEA 0183 v2+ is supposed to be differential too, but there is a lot of equipment out there that isn't differential and doesn't have opto-isolators in them. Many, but not all, ICs used for RS-232 work for both 12V and 5V - it all depends on the threshold used. A 7V threshold is not going to work with 5V signals, but a 3V will.

In the real world I suspect that very few GPS receivers have opto-isolation. Marine devices with NMEA certification almost certainly do, as that is the spec. Considering the cost to join the NMEA club, buy the specs, and get products certified, it is understandable that there are a lot of "NMEA compatible" products out there that interoperate but don't meet the spec.

Greg

Just got my new marine gps that i linked a few posts ago and took a few minutes to hook it up and it works on my M-502.

Instructions are not real clear, so this might help

Connection to RED rca jack (not white) yellow data wire to outer connection and green data wire to center hole connection.

Of course red to 12 volts and black/shield to negative.

;-)

[RaymondR]

Originally Posted by CarinaPDX

NMEA 0183 v2+ is supposed to be differential too, but there is a lot of equipment out there that isn't differential and doesn't have opto-isolators in them. Many, but not all, ICs used for RS-232 work for both 12V and 5V - it all depends on the threshold used. A 7V threshold is not going to work with 5V signals, but a 3V will.

In the real world I suspect that very few GPS receivers have opto-isolation. Marine devices with NMEA certification almost certainly do, as that is the spec. Considering the cost to join the NMEA club, buy the specs, and get products certified, it is understandable that there are a lot of "NMEA compatible" products out there that interoperate but don't meet the spec.

Greg

I seem to recall the electrical spec is RS422 so most manufacturers would just put an off the shelf RS422 comms chip in. And, I also suspect that most RS422 comms chips would be opto isolated anyway.

[CarinaPDX]

Yes, the spec is RS-422 for NMEA 0183 v2.x+ But a lot of (not-certified) equipment is actually RS-232 and just counts on interoperabiity. When I first started messing with this stuff people kept telling me to use RS-232 interfaces, which usually worked OK for them. Fortunately I was a Mac user, and the Mac local networking (AppleTalk/LocalTalk) at the time (yes, decades ago) was based on RS-422 so eliminated any problem. These days RS-422 to USB adapters, some with optical isolators, are more common and should be used - but usually aren't. Part of the problem is that the original NMEA 0183 v1.x was RS-232 based, which has led to no end of confusion. And it is very common to mix versions in a network, which usually works. It really was/is a mess.

Greg