USB GPS receiver
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I found a USB GPS receiver in my Junque Box. It originally came with a Microsoft GPS app, but I never used it for that. When I plug it in, here's what is displayed:
ugen0.3: <Prolific Technology Inc. USB-Serial Controller D> at usbus0
uplcom0 on uhub0
uplcom0: <Prolific Technology Inc. USB-Serial Controller D, class 0/0, rev 1.10/3.00, addr 23> on usbus0On the NTP serial port config, I see my choices are cuaU0, cuau0 and cuau1.
I assume I should be using cuau0. The receiver is SiRF, which appears to be supported. I have been looking at the pfSense manual, but I'm not sure what I should be configuring. I am aware a USB connection is not as precise as a serial port, but don't know how much difference.
Suggestions?
tnx jk
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It should be cuaU0. The upper case U denotes a USB serial port.
USB connected GPS generally doesn't support the PPS signal that gives the high accuracy and in addition the USB conversion adds variable latency. The accuracy you get will usually be worse that using public ntp servers. But it will work when you WAN is down. It's cool to see the location link on the dashboard widget.
Configure it on the ntp > Serial GPS tab. There is usually some tuning to be done on the two fudge times to get it accurate enough for ntpd to accept it.
Steve
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Well, that's a bit better. It's now listed in the status.
I guess that Unreach/Pending means it's not getting a signal.
But it will work when you WAN is down.
We had a 14 hour failure on July 8. It took out Internet, IPTV, home phone and cell phone service. It was caused by a router software update.
It's cool to see the location link on the dashboard widget.
I have the NTP status widget. Is there another one?
tnx jk
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@jknott said in USB GPS receiver:
Is there another one?
Nope. You will see the link to Google maps there when it see a valid NMEA signal.
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It looks like I may be out of luck.
I have a GPS test app on my cell phone. Inside my condo, it occasionally shows 1 or 2 satellites. When I step outside, I have 24 in view.
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Mmm, well that won't help!
First troubleshooting step though is disable it in ntp and just connect to it from the command line. Make sure it's outputting _something _ at the baud rate you expect.
Steve
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I hooked it up to my Linux computer and used minicom @ 4800 b/s and get this:
$GPRMC,000103.044,V,,,,,,,110905,,,N43
$GPGGA,000104.056,,,,,0,00,,,M,0.0,M,,000050
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000104.056,V,,,,,,,110905,,,N47
$GPGGA,000105.045,,,,,0,00,,,M,0.0,M,,000053
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000105.045,V,,,,,,,110905,,,N44
$GPGGA,000106.045,,,,,0,00,,,M,0.0,M,,000050
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000106.045,V,,,,,,,110905,,,N47
$GPGGA,000107.056,,,,,0,00,,,M,0.0,M,,000053
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000107.056,V,,,,,,,110905,,,N44
$GPGGA,000108.045,,,,,0,00,,,M,0.0,M,,00005E
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000108.045,V,,,,,,,110905,,,N49
$GPGGA,000109.045,,,,,0,00,,,M,0.0,M,,00005F
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000109.045,V,,,,,,,110905,,,N48
$GPGGA,000110.057,,,,,0,00,,,M,0.0,M,,000054
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000110.057,V,,,,,,,110905,,,N43
$GPGGA,000111.045,,,,,0,00,,,M,0.0,M,,000056
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000111.045,V,,,,,,,110905,,,N41
$GPGGA,000112.045,,,,,0,00,,,M,0.0,M,,000055
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000112.045,V,,,,,,,110905,,,N42
$GPGGA,000113.057,,,,,0,00,,,M,0.0,M,,000057
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000113.057,V,,,,,,,110905,,,N40
$GPGGA,000114.045,,,,,0,00,,,M,0.0,M,,000053
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000114.045,V,,,,,,,110905,,,N44
$GPGGA,000115.045,,,,,0,00,,,M,0.0,M,,000052
$GPGSA,A,1,,,,,,,,,,,,,,,1E
$GPRMC,000115.045,V,,,,,,,110905,,,N45
$GPGGA,000116.057,,,,,0,00,,,M,0.0,M,,000052
$GPGSA,A,1,,,,,,,,,,,,,,,*1EI suspect it's working or at least would if I had a decent signal. PfSense saw it, when I selected the right com port.
According to that GPS test app, I have a decent signal at the other end of my condo, but that's quite a way from my "office".
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Yup, it's sending NMEA sentences at the expected baud rate. Just no data, presumably because there's no signal.
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it occasionally shows 1 or 2 satellites. When I step outside, I have 24 in view.
You need at least three for rough location data. I'm guessing the timing signal will come with the location sentence (its been awhile since I've done NEMA stuff).
With 4, you'll start to get error correction, and each subsequent satellite with make it "better".
An external antenna (as big as possible if you're indoors, better will be something you can put outside) will help here if the device supports it. If it doesn't have an external antenna, you may have to arrange for the device to be outside for good reception. I have a little USB one myself, and it works best when the magnet has it attached to the top of the truck - not so good even when its in the truck.
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Yeah, I used a USB extension cable to get the receiver out the window. Works fine there, for what it is (no PPS).
Steve
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The problem here is the building my condo is in. Outside my window is a walkway connecting the units and then stairs beyond that. So, even when I'm right next to the window, I'm still quite a way from "outside". At the other end of my unit, the window really is next to outside and I can get satellites there. I've long had RF problems here, whether it's cell phones or broadcast radio. I use Wifi calling on my cell phone for that reason.
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For me, I'd have to use an extension through the wall and over a walkway, before I can get a decent signal.
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@jknott
Yup. "Clear view of the sky" is a general GPS requirement for both signal strength AND being able to see enough satellites. The signals aren't overly strong to start with, and once you do start any penetration with a density higher than "sea level air", you'll start to pick up distortions pretty quickly. -
@bmcgover said in USB GPS receiver:
The signals aren't overly strong to start with
That is a massive understatement.
When you look into GPS you find it requires some engineering blackmagic to detect the signals at all even in the best conditions. Something everyone takes for granted these days.
