GTM-21 & cradle receiving voltages

Cypermethrin · Occasional Visitor Joined: Sep 03, 2009 Posts: 9

Can anyone advise me if the GTM-21 flat plug, which feeds the Garmin cradle, is 12v ? And is then taken directly by the Garmin nuvi 760 and used ?

I know that if you use the USB connector the 12v is stepped down to 5v before entry into the unit.

I have taken some readings of the voltage inside the Garmin cradle at 12v which implies the step down is not required if you use the Cradle ?

Thanks

PhilHornby · Posted: Mon Sep 07, 2009 9:24 am Post subject:

Yes, it is.

If you go into the 760's diagnostic screen (by holding the battery icon for 7 secs), you can see the external voltage detected by the unit.

I sometimes run my 760 on the bench, powered from a 12V unregulated adaptor, via a StreetPilot's straight-through connector. The Nüvi hasn't objected (yet!) to the 13.75V it is being fed with.

Cypermethrin · Occasional Visitor Joined: Sep 03, 2009 Posts: 9

Thanks Phil

Just to clarify you can feed the 760 with 12v through the cradle via the GTM-21 gizmo. But can you also feed it 12v directly through the mini-USB 5 pin plug too ?

PhilHornby · Posted: Mon Sep 07, 2009 10:18 am Post subject:

Cypermethrin · Occasional Visitor Joined: Sep 03, 2009 Posts: 9

PhilHornby · Posted: Mon Sep 07, 2009 2:01 pm Post subject:

Are trying to avoid using the cradle?

Otherwise, wouldn't the easiest way, be to plug the GTM-21 into a cigarette lighter extension cable, which has the plug chopped off and connected to the fuse-box instead. You could put your USB extension lead in place for data transfers.

Otherwise, the problem you have got, is accessing Pin 4 (ID) of the mini-usb socket (there being 5 pins in total). If you were to plug a Garmin 5V adaptor in, at the end of a USB 'extension', the Nüvi would go into data-mode. It needs to sense the resistance between Pins 4+5, to know it's a different kind of peripheral attached. I don't think you can buy a mini-USB extension lead with all 5 pins connected. (Strictly speaking, the USB spec. doesn't allow for extension leads at all Surprised

)

Cypermethrin · Occasional Visitor Joined: Sep 03, 2009 Posts: 9

Hi Phil

Thanks for your help here- much appreciated. The pictures below should help explain the dilema. The plastic adaptor which has to be glued to the rear of the fascia holds the GPS. You then make holes in it to gain access to the ports. So if I used the GTM-21 as you rightly suggest as being the easiest way it will most likelt foul the fit of the unit in the mould.

The alternative way is to remove the unit from the housing everytime you need to update the data/maps etc.

What do you think ? I agree using the cradle is the easiest away to achieve this - but I would have to hack a considerable amount of the rear of the mount for it to fit ?

Thanks - again....

And the finished item looks like

M8TJT · Posted: Mon Sep 07, 2009 3:11 pm Post subject:

How about reducing the size of the piccies so that they fit the page? Shocked

Cypermethrin · Occasional Visitor Joined: Sep 03, 2009 Posts: 9

PhilHornby · Posted: Mon Sep 07, 2009 11:19 pm Post subject:

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