Using Garmin GPS 17HVS NMEA with RL70C

[Tigray]

I have an RL70C that also does chartplotting. It was set up on the boat so that it gets its position info from the Northstar GPS - Northstar outputs NMEA to autopilot, then to RL70 via Seatalk (I). That part works just fine. The boat also has a Raystar 112LP Seatalk version which was intended to give the RL70C GPS data if the main GPS was out. The 112LP hasn't worked since 2003.
So the first question is: Can the 112LP be repaired? I have replaced the lithium battery, still doesn't work.
The second question is: Can I use a Garmin GPS 17HVS to provide NMEA GPS data directly to the NMEA input on the RL70? I got a GPS 17HVS for free, and I'd like to replace the 112LP with it if the 112LP can't be resurrected.

I tried hooking up the GPS 17 to the radar; GPS 17 NMEA out to RL70 NMEA in+ and RL70 NMEA in- to ground. The GPS 17 output swings roughly +5V to -5V and runs at 4800 baud. Doesn't work. There is no separate NMEA out- coming from the GPS 17. Is +/-5V enough swing, do I hook it up some other way, got any ideas?
Thanks!

[Chuck - Raymarine - Moderator]

Q1. Can the 112LP be repaired? I have replaced the lithium battery, still doesn't work.
A1. Unfortunately, Raymarine's Product Repair Center can no longer repair this model of GPS sensor. It it is not operational, then it is recommended that it be disconnected from the system.

Q2. Can I use a to provide NMEA GPS data directly to the NMEA input on the RL70? I got a GPS 17HVS for free, and I'd like to replace the 112LP with it if the 112LP can't be resurrected. I tried hooking up the GPS 17 to the radar; GPS 17 NMEA out to RL70 NMEA in+ and RL70 NMEA in- to ground. The GPS 17 output swings roughly +5V to -5V and runs at 4800 baud. Doesn't work. There is no separate NMEA out- coming from the GPS 17. Is +/-5V enough swing, do I hook it up some other way, got any ideas?
A2. Should the Garmin GPS 17HVS support 4800 BAUD NMEA 0183 v2.1 or higher communications protocol, then it may indeed be interfaced to the RL70C's Power/NMEA 0183 Input Cable. Please note that this generation of products is not designed to support multiple sources of any specific data item (ex. lat, lon, COG, SOG, depth, etc.). Accordingly, the RL70C system should only be interfaced to on source of each type of data.

If it is compatible, the GPS17HVS NMEA 0183 OUT+ lead (white) will be interfaced to the NMEA 0183 IN+ (orange) lead. The GPS17HVS ground lead (black) will be interfaced to the NMEA 0183 IN- (yellow) lead. The remaining leads of the GPS sensor should then be interfaced to power and ground per the GPS sensor's installation guide.

I tried hooking up the GPS 17 to the radar; GPS 17 NMEA out to RL70 NMEA in+ and RL70 NMEA in- to ground. The GPS 17 output swings roughly +5V to -5V and runs at 4800 baud. Doesn't work. There is no separate NMEA out- coming from the GPS 17. Is +/-5V enough swing, do I hook it up some other way, got any ideas?

[Tigray]

Chuck, thanks for the info.
Connecting the GPS17 directly doesn't work. The Northsar NMEA output swings 0-5V, this works on the RL70 NMEA input. So I decided to develop an interface circuit to translate the -5V to +5V signal from the GPS17 to 0 - 5V. I used an old CMOS logic IC, a CD4009 hex inverter to do the job. I applied 5V (from a cigarette lighter USB cellphone charger power adapter) to VCC and VDD, Ground to VSS, the GPS17 output in series with a 10K resistor to one inverter input, that inverter output to another inverter input, then the second inverter output goes to the RL70 NMEA input. Also tie the other four inverter inputs to VSS. The input diodes on the CD4009 work with the 10K resistor to clamp the -5V/+5V signal to 0/5V so the output of the second inverter is a 0 to 5V swing in phase with the GPS17 output. This works nicely. Probably any 5V supply CMOS logic chip providing inverters or buffers will work if you can't find the old CD4000 or 74HC chips. I do see 74HC chips on Ebay and Amazon.
Thanks for the tip on only having one source for GPS data input into the Raymarine units, I will install a separate power switch for the GPS17 so I can have it active only when the Northstar is inactive.

[Chuck - Raymarine - Moderator]

You're welcome.