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Old 28-08-2015, 11:20   #1
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No GPS if laptop is charging. strange

Strange issue with new setup. I've been using opencpn for several years with a usb GPS puck on my laptop. I just installed a standard Horizon GX2200 with GPS and AIS. I set up a serial to USB cable to input the gps and AIS signal to the laptop. I did a temporary setup and it worked great. After I ran the permanent wiring i couldn't get any GPS on opencpn. After several hours of checking all connections, i pluged my old puck GPS in and it didn't work either. I decided to give up for the day and try a different laptop later. When I unplugged my 12 V laptop power supply, the GPS indicator on opencpn immediately lite up! Plug it back in and it stops.

So running on battery I get GPS and AIS working. Hook up the charger and signal is lost. NEMA debug window is blank when plugged in. Any Ideas?

Richard Hess
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Old 28-08-2015, 11:35   #2
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Re: No GPS if laptop is charging. strange

I have a dell laptop.

If I plug in the printer I lose wifi connection. I think the power connection of the usb also feeds the wifi module. Too much output and its not going to work. My usb puck also has difficulty working.

I have not tried it on battery only.... I suspect it is a similar issue.

I recently bought an Acer..... no problems.
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Old 28-08-2015, 11:40   #3
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Re: No GPS if laptop is charging. strange

Radio Frequency Interference from the 12V laptop supply?

Please clarify though: Do you still have the GPS puck? Or is your GPS source the Standard Horizon radio? When you lose GPS on OpenCPN, do you also lose it on the radio?

Are you getting *any* data through the serial/USB cable? If GPS is the only thing affected, and the radio also loses it's GPS data, then it might be RFI from the supply. Normally I wouldn't expect this to be a problem with GPS, since the GPS frequencies are much higher than the typical static put out by even a noisy supply. But noise can act in surprising ways. I would put ferrite clamp-on cores in the wires to and from the laptop supply and see it that helps.

If the serial connection has gone totally dead, then it's probably not RFI, but it's still noise of some sort. In that case the ferrites likely won't help but they are still worth trying. Next step is to try a different power supply.
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Old 28-08-2015, 12:25   #4
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Re: No GPS if laptop is charging. strange

It is possible that the power supply is creating RFI that knocks out the GPS signal, but if you used to use the old GPS while this same computer was charging and had no problems then, that would point to something about the new wiring or new setup. Still, if you can find another laptop it might pay to set up the other laptop, then plug in the troublemaker for charging and see if simply having that power supply hooked up and running can kill a GPS that is "next to" it.


Eliminate the simple "Oh, it couldn't possibly be..." things first, and the problem will pop out.
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Old 28-08-2015, 12:49   #5
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Re: No GPS if laptop is charging. strange

Aw, come on now. $5 bucks says you've got one of the data and ground wires in the cable converter to the laptop's USB reversed. Maybe from the factory (reverse vs straight or vice versa), or maybe if you wired them.

If there is no chance of that based on how you came by the cable, then verify the data converter needed from your nav equipment to the PC's USB is rs422 vs rs232 - verify you bought the right cable converter.

And lastly, did you blow that USB port with reversed cable or connections?

Its gotta be one of these, but $5 says wires are reversed.
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Old 28-08-2015, 12:52   #6
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Re: No GPS if laptop is charging. strange

I will try another laptop. The GPS on the radio and chart plotter work fine when the laptop doesn't. So it seems like the usb ports stop working when the power supply is plugged in. The GPS and AIS on the radio are unaffected. It must be the power supply because it is a DC to DC converter not the normal AC power supply. I'll also try the regular power supply. It's an Acer laptop.

BTW, the GPS and AIS are both coming from the radio on one serial cable, which contradicts everything i've seen that said i would need two cables.

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Old 28-08-2015, 12:58   #7
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Re: No GPS if laptop is charging. strange

But it works perfectly if the laptop is running on battery power.
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Old 28-08-2015, 13:34   #8
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Re: No GPS if laptop is charging. strange

Floating grounds ...

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Old 28-08-2015, 17:29   #9
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Re: No GPS if laptop is charging. strange

Tried Ac charger through inverter and same result. GPS work fine on battery power but drops as soon as charger is plugged in. Only two NEMA data wires connected to the serial to usb cable. What would be the floating ground here. No power being used from the usb port

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Old 28-08-2015, 18:24   #10
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Re: No GPS if laptop is charging. strange

"GPS and AIS are both coming from the radio on one serial cable, which contradicts everything i've seen that said i would need two cables."
On a serial bus, you can have multiple "listerners" with one "talker". Or, multiple talkers. However, if two devices both "talk" at the same time, and there is (typically) no collisional control, you'll sometimes get gibberish when two or more try to talk at once.


With new devices and gear like AIS which may be trying to send a LOT more data than anything sent in 1980, that's when having multiple talkers on the same line gets problematic.




On the power supply...floating grounds could indeed be part of the problem. Some systems are 'staked' to a zero volt negative and fixed positives about that, i.e. +5vdc, +12vdc. There were some infamous Dell laptops that used 5V instead of 12V on their serial ports, and there are other "things you can get away with" that don't always work. So it could be something besides RFI but if it is one of those things, the odds are there's not much you can do to correct it. At this point, all you can do is try to pin down the specifics. (Or, randomly throw money at alternatives that might work.)
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Old 28-08-2015, 22:09   #11
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Re: No GPS if laptop is charging. strange

And is one of the two nema wires a ground?
-If not, why is there not a ground wire.
- If so, did you reverse thier pin connections?

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Old 29-08-2015, 10:54   #12
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Re: No GPS if laptop is charging. strange

The only lines hooked up are the NEMA + and - data lines. I think that that is not the same as a ground? Should I hook the serial ground pin to the ground wire on my boat?
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Old 29-08-2015, 11:31   #13
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Re: No GPS if laptop is charging. strange

Originally NMEA0183 is RS422 which has 2 datalines, line A and line B.
A computer knows however only RS232 and without the 9pin connector can have virtual RS232 ports using an USB converter. RS232 has one dataline only and ground line for receiving data. So he needs line A and ground of RS422 which works in most cases because there is only a very small difference in voltage levels between RS422 and Rs232.

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Old 29-08-2015, 12:17   #14
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Re: No GPS if laptop is charging. strange

[deleted]

It turns out that the SH GX2200 puts out standard balanced NMEA levels. My older model sends unbalanced, but the new model has changed that.
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Old 29-08-2015, 12:32   #15
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Re: No GPS if laptop is charging. strange

Quote:
Originally Posted by sailouterbanks View Post
The only lines hooked up are the NEMA + and - data lines. I think that that is not the same as a ground? Should I hook the serial ground pin to the ground wire on my boat?
Do not connect the "NMEA -" output signal to the RS232 adaptor. Instead, connect your RS232 ground to your 12V ground (the same ground that connects to the SH GX2200 radio). Do connect the "NMEA +" signal to the adaptor.

This probably explains why your data goes dead when you connect the charger to the computer.

Here is the manual for the GX2200: file:///C:/Users/Paul/Downloads/GX22..._EM044N170.pdf. Page 20 describes the NMEA hookup.
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