Thursday, August 21, 2014

APRS to Garmin Waypoint

GPSMAP 64s, Yaesu VX-8G & powerbank

In this blog entry, I will be talking about integrating APRS to a Garmin GPS receiver with active waypoint. Some of the APRS products does support sending received RF packets with current position as a waypoint directly to a Garmin GPS. I believe Yaesu, Kenwood and NET51TNC support this feature.

A while ago during an eyeball session with 9W2KHN, 9W2WHT, 9W2CEW and myself, 9W2KHN mentioned that it would be really cool if we can integrate active waypoint for any received APRS packets to a Garmin receiver on a colour map. As I still have my first generation Garmin colour screen, GPSMAP 60C, we went ahead to test this out.

Before we continue, let talk a bit about serial protocol commonly used in modems and console to network appliance. There are two types of serial protocol, they are RS-232 and TTL (Transistor to Transistor Logic ) and both have different electrical characteristic.


- RS-232 serial protocol that runs on inverted logic: -12V for TRUE(1) and 12V for FALSE(0)

- TTL serial that runs on 0V to 5V ( or 0V to 3.3V ) with 0V for FALSE (0) and 5V for TRUE (1).

If you ever need to communicate one way from RS-232 to 5V TTL, placed a 22k ohm resistor on the Tx of RS-232 to Rx of TTL.

Let's get back to the main topic of connecting a Yaesu VX-8G to Garmin GPSMAP 64s, for Yaesu VX-8G, the 2.5mm 3-pin PTT out have RS-232 electrical signals and works best with older Garmin models with the round Garmin port that have the same RS-232 voltage level.

Garmin connector

For our first tests, we did a direct connection from BH4TDV NET51TNC to Garmin GPSMAP 60C for a TWO way communications, Garmin send the GPS position to the 51TNC and the 51TNC send any received APRS packets with position as a waypoint to the Garmin GPS receiver.


MAX232 on prefboard

As we did not want to pull the internal jumpers to switch to RS-232 signals, we added a MAX232 IC in between to convert between RS-232 signals to TTL signals.

Garmin GPSMAP 60C with APRS waypoint
The above picture is the captured Garmin waypoints from the air. The NET51TNC still have some bugs on the SSID and could not decode compressed packets and will give an error when it received any compressed APRS packets as a waypoint. BH4TDV will fix this for the next firmware upgrade (hopefully).

Here is a better picture from 9W2KHN NET51TNC to Garmin Oregon 450 with distance and headings to the waypoint. The Oregon 450 uses a mini-USB.

For the below setup of Yaesu VX-8G with Garmin GPSMAP64s, with the cable, 2.5mm Yaesu on one side and mini-USB on the other with a MAX232 in the middle. 5V power will be supplied using a power bank to both the MAX232 and Garmin GPS.

Here are some of pictures and screenshots from the Garmin GPSMAP 64s with GPS/GLONASS receiver from 9W2WHT.

Garmin GPSMAP 64s
APRS waypoint

Finally the completed cable for this project nicely done by 9W2WHT.

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