wiring the Mobilinkd TNC & automatic on/off (Jeep tablet based APRS part 2)


in the last post about APRS i explained why i was interested, where the Mobilinkd bluetooth TNC fit in, and how to get the basic radio/TNC/tablet setup working.

as promised, i’m following up now that i’ve gotten everything in its final configuration for backcountry use. this post will cover installing the Mobilinkd in a vehicle.


wires, wires, wires

it appears the Mobilinkd doesn’t need much more than half an Amp even when charging a dead battery. once the battery is topped off, current draw drops to around 50 mA.


that means nearly any phone or gps car charger with a mini-usb tip should work ($5 on Amazon). just be sure to get one with a mini-usb tip and not the micro-usb that has become common lately.

if you ever had a BlackBerry or other early smartphone you might already have one lying around.


i decided to hard-wire mine instead of using a cigarette lighter style adapter (to keep things tidy). i ordered a mini-usb vehicle hardwire kit from Amazon for about $10. you could make your own with a buck converter or linear regulator and mini-usb cable.



come on!

i wanted the Mobilinkd to turn on and shut off with the vehicle so i wired the power cable to a 12v switched source. this took care of shutting down automatically, but i still needed to press-n-hold the power button to turn it on.

fellow ham M1BXF had already solved that problem with his “auto power up” mod. after a quick look at the schematic i couldn’t find any better solution, so i followed his example of effectively bridging pins 1 & 3 on the U3 chip. my solder job isn’t nearly as precise as his, but works.


since the auto-on mod bypasses the soft power button and related circuitry, you must disconnect the battery and rely on the external power being switched. instead of removing the battery, i added a micro slide switch just in case i ever want to take the Mobilinkd out of the vehicle and use it with a hand-held radio.

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again, the switch above isn’t needed for a vehicle-only install. most folks would just do the auto-on mod and ditch the Li-ion battery.


everything in its place

i randomly shoved gently placed the Mobilinkd under the front of the center console. my ham radio is mounted behind the driver’s side knee panel so the TRRS to mini-DIN-6 cable easily reached. i pulled power from an existing tap on the switched accessory outlet just above the console.

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ignore the unrelated USB cable in the photo (that’s where i plug in flash drives for use with the tablet).


now to the trail! almost…

with the TNC nicely stowed and turning on/off with the Jeep, i was nearly ready to climb some mountains while beaconing.

the only glitch was that the APRSdroid app is based on Google Maps which needs an internet connection. fortunately using offline maps instead isn’t a big issue. i’ll step through setting that up next time (including road & topo maps)!

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3 responses to “wiring the Mobilinkd TNC & automatic on/off (Jeep tablet based APRS part 2)”

  1. Brian [website] Reply

    Nice write up! I recently bought a mobilinkd modem (I guess it’s not a true TNC since it needs a head) to configure for search and rescue out in the Superstition Mountains and various other parts of the desert. Getting the topos offline and being able to work with SARTrack software is what I’m shooting for. I really appreciate the information you are posting on here and sharing how you set yours up, including the bold modifications!

  2. Russ Bell Reply

    Your writeup got me interested in a portable APRS suitable for vehicle or hiking. I had a Baofeng uv5 and a Samsung Tablet. Ordered a MobilinkD to finish the package. Got it operational, then downloaded the usa.map and installed it in tablet running OSM APRSDroid. All now is working offline. Set APRSDroid path to be my callsign. Set Kenwood D700 in truck to digipeat my callsign. Now, when hiking in boonies, my position gets relay’d to APRS websites. Batteries appear to last for a day of hiking provided the tablet screen has a short timeout. I am very pleased with the setup.