I know this is sort of a late reply, but.
CanBus architecture (and NEMA is a standard related to CanBus) typically uses the voltage between + and ground for input. The voltage from - to ground is used to validate the input and to filter out interference. So a 3 wire system is basically a 2 wire system with redundancy, The wiring diagram for one of the devices on my boat actually shows a + and - NEMA input, but works just fine with only the information carried on the + and ground wires from my old Garmin GPS. On the forklifts produced by my previous employer, which used CanBus for the controls and management of performance, In a critical item like the throttle position sensor, the sensor output both a + and - voltage which should be a mirror image of each other. If the two voltages were out of sync, the controller would restrict engine performance to prevent a runaway vehicle, and set a fault code in the self diagnostics. But if the two signals from the sensor were synchronized, the controller would use the +voltage as operator input for performance desired and adjust engine speed and transmission parameters appropriately. I must say that I was incredulous when an auto maker had unexpected acceleration problems and a major recall a couple of years ago that were attributed to throttle position sensors, the potential problem and the easy fix seemed so obvious based on my experience. On a 3 wire system, both the + and - signals are influenced identically by interference. A +1.5v input becomes +1.6 and a symmetric -1.5v redundant signal becomes - 1.4v. The controller can filter out the level of the interference (up to limits defined in the software) and use the + 1.5v input. We actually had a lot of problems with trucks sold in certain environments like steel mills and power generation facilities with high magnetic fields. I suspect this data clensing potential is the value of a 3 wire input for NEMA. The point being that, since NEMA signals used in our GPS and VHF systems are not "critical" (and you will recall that "prudent mariner" statement that you aren't supposed to rely on the electronics as your only means of navigation) they only use the 2 wire + voltage connections between instruments. Rick Brass Washington, NC From: cnc-list-boun...@cnc-list.com [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Della Barba, Joe Sent: Friday, September 21, 2012 12:42 PM To: cnc-list@cnc-list.com Subject: Re: Stus-List NMEA 0183 Ver.1.5 to 3.0 Usually you can use single-ended. My GPS, AIS unit, VHF and APRS gear all use single-ended data connections. The computer is supposed to be differential but seems to read the + and ground signal just fine. Joe Della Barba Coquina From: cnc-list-boun...@cnc-list.com [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Steve Thomas Sent: Friday, September 21, 2012 12:29 PM To: cnc-list@cnc-list.com Subject: Re: Stus-List NMEA 0183 Ver.1.5 to 3.0 Seems there is an electrical difference between 0183 1.xx and 0183 2.xx and later versions. The 1.xx versions are single ended, signal and ground, while the 2.xx and later have differential + and - signal wires and should have a separate ground/shield. Funny thing is that the GX2150 does not have differential inputs. Anyway here is what one guy did to interface an RL series plotter to a GX2100. Might be worth a try. http://www.sailnet.com/forums/electronics/82335-how-connect-standard-horizon -gx2100-ais-vhf-raymarine-rl-70c-plotter.html Steve Thomas C&C27 MKIII Port Stanley, ON -----Original Message----- From: cnc-list-boun...@cnc-list.com [mailto:cnc-list-boun...@cnc-list.com]On Behalf Of Frederick G Street Sent: Friday, September 21, 2012 11:50 AM To: cnc-list@cnc-list.com Subject: Re: Stus-List NMEA 0183 Ver.1.5 to 3.0 Bill take a look at this PDF, starting with page 9: http://www.actisense.com/Downloads/TechTalk/NMEA%200183/The%20NMEA%200183%20 Information%20Sheet.pdf This might help. In my experience, sometimes there are issues with what gets labeled "input" vs. "output", as well as data + and - or ground; but be really careful what you try so you don't damage things. Usually it's just as easy as connecting the properly labeled leads together to get the signal to the proper place -- the problem comes in getting the settings right on the send and receive end, so that everything's happy. Fred Street -- Minneapolis S/V Oceanis (1979 C&C Landfall 38) -- on the hard in Bayfield, WI :^( On Sep 21, 2012, at 10:25 AM, Bill Coleman wrote: Hello Steve, This tech was pretty sharp, he was not reading from the manual - it is a 2003, so I believe him when he says it is 1.5 There also is no mention at all of versions, let alone Baud rates, , he said it was 4800, period. The only thing I can adjust in the setup is turning sentences on and off, and the seatalk bridge. I have tried connecting them, no response. The sentences are coming in, the voltage rolls up and down. I think there must be something different in the protocol between 1.5 and 2. The Standard Horizon manual definitely says it will only work with ver. 2.0 and up. I have bridged NMEA to Seatalk as that is how the Autopilot communicates, but I don't think this would be a problem, that just introduces other info such as the compass and converts to NMEA, I think. A talk with a Standard Horizon Tech produced nothing, oddly enough he didn't seem to know much about NEMA conversions. Waiting to hear back from Brookhouse.
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