GPS strangeness with carputer - works fine with laptop/pda

UrbanDragon · 01-30-2004, 07:42 PM

Hey all, I have a deluo serial GPS receiver that plugs into the ps/2 port for power, etc. If it's plugged into my laptop and sitting on my dashboard, I pick up a satellite instantly. If I plug it into my Dell Axim with the power coming from the lighter socket, it also works flawlessly.

When I plug it into my epia m1000 (150 watt power supply plugged into the same 300 watt inverter the laptop uses, monitor is a 7" lilliput with the usb touch screen) I cannot get a satellite lock unless I put it on the roof. On the dashboard it will see the satelites but never lock.

Does anyone have any ideas on what may cause this? I'm theorizing power (simply guessing really) somehow may be at fault.

This unit can also plug into a USB port with the proper adapter, I may try that to see if it makes a difference.

Any suggestions?
Thanks,

Alanh · 01-31-2004, 11:39 PM

I'm guessing too, but checking the power seems to be a good place to start. If you have a DC voltmeter, and can get access to the right pin on the PS/2 connector of the m10000 (assuming this is possible - I don't have one), try measuring the voltage of the +5V pin with and without the GPS connected to it. I don't know which pin is +5, but a search should find it.

It could be some other interface problem too, like voltage levels or timing on the signals from the GPS; or maybe some sort of conducted or radiated RF noise problem giving the GPS fits. Without the right test equipment, I don't know how you'd go about solving those problems except by and error.

If it works on the roof, I think an interface problem is less likely to be the cause of your troubles.

You've sure to have more signal strength from the satellites on the roof as well as more "visible" to the GPS which might make the difference if the receiver isn't working as well as it should. I'm guessing this might happen if the voltage into the GPS is marginal. But you've also got less possible interference from the RF noise generated by your computers and inverter.

With the GPS on the roof, you've got (I assume) the metal roof to shield the GPS from any RF noise from the other electronics. Did you have the same equipment running when you tried the GPS on the dash connected to the laptop, and when connected to the m10000? If so, I doubt radiated RF is the problem. If you didn't have the same stuff running, try that to see what results you get to help determine the cause. Note that I don't know exactly how susceptible GPS receivers are to RF noise in the first place. But, I read about some boat owners having problems because of a design flaw in a satellite TV receiver that was giving GPS receivers at quite a distance problems (don't remember exactly, but it was quite a ways - on the order of a thousand feet). The latter problem was well documented and not just guesswork because some university people tracked it down and isolated it to the units actually causing the problems.

Hope this helps,

Alan

UrbanDragon · 02-01-2004, 10:00 PM

Thanks - the only thing running is the computer & the lilliput touch screen... I'm pondering a direct DC power for the gps unit itself, Deluo sells one for $20...

none · 02-01-2004, 10:09 PM

Try to power it from the laptop while trying to use it on the EPIA.

NJay · 02-02-2004, 06:00 AM

If its working from the laptop, try running it again from the laptop but with the Epia running as well. If it works then there is no RF issue with the epia and would point more to interface/voltage issues with the epia.

UrbanDragon · 02-02-2004, 10:59 PM

Drove home tonight with the carputer running (it's in the trunk) and the GPS plugged into the lighter socket and into the PDA - got sync very quickly while driving.

Seems to be power, I believe I'll try the $20 lighter socket power option for it and see how that goes.

Thanks for the suggestions, this is the part I figured would be a no brainer of the project, and of course it's the part that's been troublesome.