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I'm trying to get one of these guys talking through a rs-232 serial port: https://support.garmin.com/en-US/?partNumber=010-00258-62&tab=manuals

There you can download the manual which has all of the technical details.

Full disclosure: I'm primarily a software developer so this stuff is entirely outside of my wheelhouse.

My setup now: I have a 24V power supply (so acceptable voltage) but I'm having trouble confirming if the device is powered on and sending sentences (i.e. I can't tell if I'm not receiving GPS sentences because my cable pinout is wrong for the serial port or the device just doesn't have power).

This is the power supply I'm using: https://www.automationdirect.com/adc/shopping/catalog/power_products_(electrical)/dc_power_supplies/rhino_select_(din_rail)/psm_series/psm24-180s

The GPS' cable comes with a 5 pin serial port connector that you can unscrew to expose the raw pins which are held into place with screws. I've undone the screws for the red and black cables (pins 1 & 2) and I've plugged them into the power supply. Red going to a + pin and black going to a - pin.

However, I'm not sure how to confirm that the device is wired correctly and sending sentences. I've tried using an oscilloscope here but I'm kind of a noobie with that too and wasn't sure how to exactly use it to test what I think I should be seeing.

For example, I connected one part of the oscilloscope's probe to the white pin and grounded it to the black pin connected to the power supply but for some reason, I wasn't seeing anything on the scope.

Any tips or advice are very welcome. I'm largely new to electronics and troubleshooting. I do have access to both a multimeter and an oscilloscope if that helps.

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  • \$\begingroup\$ You should doublecheck the "Technical Specifications" datasheet that you referenced. On Page 8, it has diagrams showing how to connect the cable to both male and female DB-9 connectors. One special thing to note: The yellow wire is "Remote ON/OFF" and also needs to be grounded for the module to function. \$\endgroup\$
    – Andrew Lentvorski
    Sep 17, 2021 at 7:53
  • \$\begingroup\$ Ah good, I wasn't sure about this part actually. You're completely right, the yellow pin needs to share the ground. I finally realized, the oscilloscope I was using was in "trigger" mode instead of continuously capturing. I've since figured out the scope and using that, I was able to confirm that yes, I've wired the GPS correctly to the power supply and it actually works! \$\endgroup\$
    – exbigboss
    Sep 17, 2021 at 22:32

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I briefly checked the Garmin datasheet saying:

True RS-232 output, asynchronous serial input compatible with RS-232 or TTL. ...

You didn't share details about your interface but I assume it is either native PC computer RS-232 port (getting rare these days) or an USB to RS-232 adapter. That should be compatible. You may start opening a terminal (Teraterm, PuTTY, etc.) and selecting the given COM port. Assuming you have DB-9 connector on the RS-232 port, disconnect it from your GPS, short pins 2 and 3 and see if typed characters get received back on the terminal. At the same time you you may verify your oscilloscope method and scope the characters you are sending. If you verified this end works it may be the time to try with the GPS again.

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  • \$\begingroup\$ Thank you, this is good advice. I've finally figured out the scope and I've confirmed that I've wired it correctly. It's just a matter of fixing the pinout now. Thank you for the help! \$\endgroup\$
    – exbigboss
    Sep 17, 2021 at 22:34

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