OpenMarine

Hello Hardware Interface Wizards,

I have Garmin GPSmap 78sc(a handheld) and the cable with the 4-pins to "OUTPUT DATA STREAM".
It can send very stable GPS and Compass data, so I want to use this on-hand device in OpenPlotter.
The firmware within the 78sc is set to output, and seems to be working, so the question is just hardware at this point, thanks

The question is: How do I get the Garmin data into my Raspberry Pi OpenPlotter/SignalK system?

I think I need an RS232 or RS422 or ?? voltage level converter of some type.

The cable also supplies 12vdc to the Garmin, so I think the voltages will be above 5vdc.

My Fluke DVM shows both positive and negative voltages, with a 'burst' type of fluctuation which I trust is Data
(yes, i need an o-scope, but mine is a victim of Ocean Aging at this point)

I expect to be soldering rtl232 chips or transistors on perf-board with an Arduino to format to JSON/Signalk to solve this

for reference, consider my 'level' as a retired EE with industrial experience unrelated to the subject herein


Thanks !

Hi,
A serial-to-USB converter, an opto-isolated one if you like, will do the job.

Ordered a RS422-USB converter from AMZN
DSD TECH USB 2.0 to RS485 Serial Data Converter CP2102 Adapter Compatible with Windows 7,8,10,Linux,Mac OS
They sent the WRONG PART (only 3 terminals , so Not Even Close)
Arrrrg AWAP again

9Feb2021 update
Tried serial converter per advise above: fail
Amazon; DTECH USB to RS422 RS485 Serial Port Converter Adapter Cable with FTDI Chip Supports Windows 10 8 7 XP Mac -1.5 Feet
set at 9600 baud (Garmin 78sc default) with NMEA output enabled on th Garmin 78sc
DVM shows activity on the Garmin cable (green lead) AC volts, Hz
SERIAL finds and connects the USB adapter OK
NO data is being indicated in the DASHBOARD

fail

I use some thing like https://www.ebay.com.au/itm/USB-2-0-To-R...SwudRfvkZ6 this with my Garmin72H and Garmin73 and have never had a problem i am only receiving data from the Garmin so the 2 wires work..... The only fault with this type of unit is the A & B terminals are incorrectly marked on the unit so Ground to A and Data to B and you should find it works.

These also work well http://www.yakbitz.com/Yakker.aspx send GPS NMEA data via wifi easy set up and low power.

good luck