Why does Garmin satnav see charger as a PC?

fwor

Just bought two new cheapo in-car mini-USB power supplies to hide away under the dash (so as to not have a trailing lead from the cigar lighter socket).

Problem is when either is plugged into the satnav and powered on the satnav seems to think it is connected to a PC, so all it shows is the picture of a wire going to a PC.

With the original Garmin car power supply it works normally.

Anyone know why it's doing this?

SandLake

Have a look here

http://www.pocketgpsworld.com/modules.php?name=Forums&file=viewtopic&p=585551&highlight=#585551

fwor

Thanks - I've been doing some searching myself, and not found a definitive explanation. One possibility is that the Garmin chargers output a very specific voltage, and generic ones are not quite right. The generic ones are definitely higher (5.2 volts versus 5.03 for the original)

For me, an adequate work-around is to switch the unit on (on internal battery), press the battery status area for 8-10 seconds until it goes into test mode, then connect the charger. Then pressing Exit makes it operate normally.

The other option ~might~ be that an original Garmin charger puts 0 volts on two pins and 5 volts on the other two, while a generic charger should only use the outer two pins and leave the centre two unconnected. Unfortunately the plug is too small for me to be able to test this without risking shorting it out...

fwor

After a bit more research it seems that from around 2007 onward, devices can check the status of the D+ and D- data lines, and if the two are shorted together, infer that the connected device is a charger with no data transfer capability.

If so, it's possible that a genuine Garmin charger obeys this standard and my generic chargers do not. I'll probably never know for sure...

Gloomendoom

fwor wrote: »

After a bit more research it seems that from around 2007 onward, devices can check the status of the D+ and D- data lines, and if the two are shorted together, infer that the connected device is a charger with no data transfer capability.

If so, it's possible that a genuine Garmin charger obeys this standard and my generic chargers do not. I'll probably never know for sure...

Thanks for posting this, I've had the same problem with cheapo car chargers. However, my HTC phone car charger works fine.

I'll have a play and short the D+ and D- on one of the cheapo chargers and see what happens.

John_Gray

You could always invoke the conspiracy theory that Garmin want you to use only their chargers, and arrange their wiring accordingly?

roddydogs

Just out of interest, where does the other end of the mini usb go to connect to the car? can all cars do this? Ta

Norman_Castle

I've used a satnav as a satnav while plugged into a pc by covering the central two pins in the full size usb plug with sellotape. Bit tricky with a mini usb. Mini usb to full size usb converter may help.

Edit. The above worked with a 2001 pc. Tried today with a newer laptop and got a dim screen and shutdown of the satnav.

fwor

Gloomendoom wrote: »

I'll have a play and short the D+ and D- on one of the cheapo chargers and see what happens.

That was my cunning plan too.

Thwarted by the fact that el cheapo power supply makers are so cheap, they only have 2-wire cable to the plug!

So any shorting would have to be done at the plug end. It may be possible, but it would need some very delicate surgery on a plug that small...

fwor

roddydogs wrote: »

Just out of interest, where does the other end of the mini usb go to connect to the car? can all cars do this? Ta

Nothing too clever involved here, I'm afraid.

All I'm doing is taking a car cigarette lighter USB power supply - which has the power supply built into the lighter plug and a trailing mini-USB type B, chopping the cigarette lighter plug end off and hard-wiring it to an ignition-controlled 12V supply under the dash.

The only slightly clever bit is to wire in an override switch so that the satnav can be on while the ignition is off (basically so that I can plan routes while parked up on a camp site).

fwor

Gloomendoom wrote: »

I'll have a play and short the D+ and D- on one of the cheapo chargers and see what happens.

Incidentally I've just spent a massive £1.60 on a mini-USB socket to mini-USB plug extension lead, so I can chop into the middle and measure what's actually happening without messing about sticking pins in the plug!

Unfortunately the lead is coming from China, so it will be a few weeks before I can figure out what's actually going on...