Modifying a Garmin 276c cable for APRS use.

asteffes

Explorer
Mark wanted to know how I setup my Garmin GPSMAP 276c for APRS use with my Kendwood TM-V700A transceiver.

The 276c comes with a couple of cables if you purchase it with the "car kit" for turn-by-turn directions. You get a cigarette lighter power cord that also has a speaker built into it for the turn-by-turn voice (you guys have to try it in the Italian setting. She sounds hot.) It also includes a hardwire cable, typically used in boats when you want to wire the GPS to a sonar system. This GPS includes two built-in serial ports for use with such hardware, but they can also be utilized for APRS.

So here's what I did (unfortunately I do not have step-by-step pictures, as I did this awhile ago and was in a hurry so I neglected to take pictures.)

Take your 276c's cigarrete plug and unscrew the power plug/speaker end. Inside you'll find two leads for the power connection and two that go to the speaker. No big deal so far. We're going to remove that cord and replace it with the hardwire cord. The hardwire cord has several extra leads for the two serial ports, alarm signal and other things. We're going to take the leads for one serial port and extend them with a standard stereo headphone cord complete with 1/8" headphone plug. This will plug into your Kenwood's GPS port for serial communications with the Kenwood's built-in TNC.

Carefully de-solder the existing cable's leads from the speaker and power plug. Set the cord aside. We're done with it for now.

Take your hardwire cord and note that the various leads are all labeled as to function. Trim or tape back all the leads besides the speaker, power and one of the serial ports' two wires. We don't need the others for this project.

Re-solder the hardwire cable's speaker and power leads to the cig plug and speaker.

Now, go to Radio Shack or find yourself an old pair of headphones you don't care about. You need a headphone cord that 1. support stereo sound (three internal conductors) and 2. has a 1/8" headphone plug on the end of it.

Solder the red and white leads from the headphone cord to the serial port leads on the Garmin hardwire cord. You'll need to check the Kenwood manual for which lead (red or white) should go to the send or receive pins on the Garmin serial port. I don't happen to remember. But basically, one lead is the port's receive and that needs to connect to the Kenwood's send. The GPS' send needs to connect to the Kenwood's receive. Makes sense, right?

Solder the headphone cord's ground to the ground on the Garmin cable.

Now, button up the cig/speaker housing. Plug the headphone cord into your Kenwood's GPS port. Power up the radio and the GPS. Using your Kenwood manual's instructions, verify that the radio and GPS are communicating. If so, follow the Kenwood manual's instructions for setting up and using APRS.

The idea here is that you can have you APRS setup when you want it without leaving your GPS in plain sight all the time. Of course, you can keep your GPS mounted permanently and not use the cig/speaker housing (and instead hardwire a dedicated speaker and power connection to your rig.) But I wanted this to be easily portable and removable, so it worked for me.

Here's the end result:
 

Forum statistics

Threads
185,538
Messages
2,875,653
Members
224,922
Latest member
Randy Towles
Top