Howto: Garmin Drive 40 LMT or 240 LMT USB Cable with working Traffic - BMW F800 Riders Forum & Registry



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  1. #1
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    Hi,
    I mounted my Garmin on my F800GT, and powered it via a 12v to USB adapter. At the adpater end I used a USB cable to plug into the GPS. All worked fine, except traffic reception.
    I wasn't using the TA-10 12v adapter from Garmin, and the GPS wouldn't enable traffic reception. For me the TA-10 took up too much room on the bike, which is why I went with the 12v USB adapter you can get on ebay that are much smaller.
    After doing a bit of searching, it seemed a resitor, 17K4 was in play on pin 4 of the USB end. But some people wrote it was connected to pin 5. I had a partially broken Garmin TA-10, so I took that apart to check the pin out. I discovered on my adapter that this was not connected to pin 5, but the metal case.
    My goal was to be able to use a custom USB cable with my Garmin GPS, and have traffic info.

    Pin 1 5v
    Pin 2 Connected to 3
    Pin 3 Connected to 2
    Pin 4 17K4 to outer case
    Pin 5 Ground

    Middle wire = 5v
    Sheath wire = Ground

    After making these measurements, I built myself a custom cable, with pins 2 and 3 shorted together, and pin 4 connected to the outer case with a 17K4 resistor. Pins 1 and 5 for power. What is important is, that it seems the wires for pin 5 or pin 1 are used as the antenna. You must make the cable using unshielded cable. If the cable is shielded, then the signal is too weak. My first cable was built with shielded cable.

    I tested this on my Garmin Drive 40, and it works great. I also had a Garmin 240 LMT, which is pretty much the same 4.3 inch size case, and that worked fine too. Those Garmin units are so cheap when buying used, I spent more money buying the parts to make the cable that the GPS itself !!! But the GPS is great. Its not waterproof, but I hardly ride in the rain anyway, and my mounting is inside the fairing, so it has some protection anyway.

    Click image for larger version. 

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  3. #2
    Daboo's Avatar
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    For making the GPS waterproof, I've seen videos where they used a bead of silicone on the screen edges to seal them off. For the openings in the back, I've used black duct tape.

    Chris
    Elnathan - 2014 BMW F800GT
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  4. #3
    N4HHE's Avatar
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    Pin 4 of the mini USB connector is intended to signal whether a host or a device is connected. Convention is to ground or N/C. However Garmin uses a resistor to ground to signal "special Garmin cable".

    I think you will find pin 4 of the big A connector on the other end is connected to pin 5 and the shield case on the mini end.
    2016 Yamaha FJR1300A; 2016 Beta 430RS; 2007 BMW F800S; 2009 Husaberg FE450; 2016 Subaru Outback; 2018 F150; 2013 Tesla Model S 85; 1983 Porsche 928S; 9 cats 

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  6. #4
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    Thats a good idea to waterproof the unit. I'll get round to doing that one day !

  7. #5
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    Quote Originally Posted by N4HHE View Post
    Pin 4 of the mini USB connector is intended to signal whether a host or a device is connected. Convention is to ground or N/C. However Garmin uses a resistor to ground to signal "special Garmin cable".

    I think you will find pin 4 of the big A connector on the other end is connected to pin 5 and the shield case on the mini end.
    The Garmin charger cable just disappears into the charger unit, there is no USB on the other end. When I cut the cable, just pin 5 and pin 1 were connected. Pin 4 wasn't connected to pin 5, just to the outer USB macro case. At leasst that is what I measured. When I bent open the USB end, I might have disconneted a potential connection between pin 4 and pin 5, but I don't think so, I only bent the casing near the opening.

  8. #6
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  9. #7
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    I just posted a couple of photos showing the 240 LMT and the Drive 40 LMT with the USB cable being powered from a phone charger. Traffic works nicely

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  11. #8
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    The cable has been working nicely, but vibrations have resulted in a poor connection. At speed, with throttle, on a motorway, there is a lot of vibration. The USB is not connecting good enough, and eventually starts to play up (too many quick power connect/disconnect).
    So in theory all works well, but if you can't isolate the vibrations, they get through in the end.
    I guess I could improve my mounting, but I've now purchased a Garmin 396, with a standard two pin power connector. It has pretty much identical software when it comes to displaying navigation. It works very well (but cost 10x more than my low budget solution !).
    I tried an interim fix with one of the Drive 40 units, and opened it up and soldered a USB cable directly to the board, to connect 5v. But it not a solution. The display brightness won't go above 70% when powering it like that. I guess it also needs pins 2/3 and pin 3 setup too. But then hard wiring them would prevent downloads to the device. It could be possible to extent the USB socket by soldering on that directly, but its so small, the chance of error is high. Now with the Garmin 396, I don't have the need anymore.

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