SparkFun Forums

[Builder1]

Hi,
I bought an EM406A module a couple of weeks ago. I connected it to the serial port of my PC through a level converter(2.85 to 5v) and a MAX 232 circuit.
I configured the hyperterminal of the PC to work at 4800 baud rate, and 8 bits and one stop bit, no parity.
However,the GPS module is not locking at all. The LED does light up continually. But I'm getting the output in the following manner:
$GPGGA,164310.088,,,,,0,00,,,M,0.0,M,,0000*57
$GPGSA,A,1,,,,,,,,,,,,,,,*1E
$GPRMC,164310.088,V,,,,,,,060710,,*2E
I've kept the receiver on for quite some time now (around 30mins) but still the GPS doesn't lock.
What could be the problem here?
Is there some problem with my connections?

[sylvie369]

Where is the module located? Does it have a good view of the sky?

Does the "164310.088" reflect the current time? Does it eventually change as time passes?

If you're getting those data, I'm pretty confident there's nothing wrong with your communications settings or the wiring of power, ground, and dataout from the GPS module (but are you powering it with 5V, as per the datasheet?). I have, however, recently found that a GPS circuit of mine that works fine on a breadboard takes forever to get satellite lock, and loses the lock easily, when mounted on a pc board (of my own design). I haven't identified the culprit, but it seems that it's possible to set these things up incorrectly, so that you have satellite lock problems even when everything else is fine.

[Builder1]

The Module isn't exactly located under the open sky...but about 2 meters from a window.
The "164310.088" doesn't refer to the current time, but yes this value is increasing per second, it's a totally random value.
For example another test I just did displays the following data on the screen:

"
$PSRFTXT,Version:GSW3.2.4_3.1.00.12-SDK003P1.00a
$PSRFTXT,Version2:F-GPS-03-0701301
$PSRFTXT,WAAS Enable
$PSRFTXT,TOW: 241779
$PSRFTXT,WK: 1591
$PSRFTXT,POS: 6378137 0 0
$PSRFTXT,CLK: 96250
$PSRFTXT,CHNL: 12
$PSRFTXT,Baud rate: 4800
$GPGGA,190925.545,,,,,0,00,,,M,0.0,M,,0000*54
$GPGSA,A,1,,,,,,,,,,,,,,,*1E
$GPRMC,190925.545,V,,,,,,,060710,,*2D
"

but as you can see in the sample taken next,:

"
$GPGGA,190926.500,,,,,0,00,,,M,0.0,M,,0000*56
$GPGSA,A,1,,,,,,,,,,,,,,,*1E
$GPRMC,190926.500,V,,,,,,,060710,,*2F
"

the value "190925" got incremented by one...and so on...

Yes I am powering the circuit with 5V ( i. e Vin=5V) although the TX, RX voltage levels are at around 2.7v to 2.8v...
Thanks!
P.S: If it helps, in this case, I've breadboarded the design...

[Builder1]

Is it okay if I remove the level shifter stage and directly connect the 2.8V TX/RX terminals of the EM406A to the 5V TX/RX output of the MAX232? Has anybody tried this? Does it work? (Hope my GPS won't blow up due to this after a few attempts)

[SFE-Nate]

Is it okay if I remove the level shifter stage and directly connect the 2.8V TX/RX terminals of the EM406A to the 5V TX/RX output of the MAX232? Has anybody tried this? Does it work? (Hope my GPS won't blow up due to this after a few attempts)

Yep, it works. I even have a schematic and SparkFun product to back up the claim:
http://www.sparkfun.com/datasheets/GPS/ ... 0B-v20.pdf

The Module isn't exactly located under the open sky...but about 2 meters from a window.

If you are inside a massive concrete building you won't get a lock.

I have, however, recently found that a GPS circuit of mine that works fine on a breadboard takes forever to get satellite lock, and loses the lock easily, when mounted on a pc board (of my own design).

This is a long shot but that might be due to the ground pour on the PCB. Except I have seen the EM406 mounted on 2 layer PCBs that have 1Oz copper pours on both top and bottom. The module worked fine. Like I said, a long shot.

[follower]

Does the "164310.088" reflect the current time? Does it eventually change as time passes?

Note that this will be the current UTC time, not your local time. So, in this case it was ~2:43pm UTC. An easy check is if the minutes figure is the same as local time.

--Philip;

[sylvie369]

I have, however, recently found that a GPS circuit of mine that works fine on a breadboard takes forever to get satellite lock, and loses the lock easily, when mounted on a pc board (of my own design).

This is a long shot but that might be due to the ground pour on the PCB. Except I have seen the EM406 mounted on 2 layer PCBs that have 1Oz copper pours on both top and bottom. The module worked fine. Like I said, a long shot.

The board (which I designed) does not have a ground plane at all. I'll put images of the .brd file here, on the assumption that the OP might be interested in the board design issues as well.

It was suggested to me elsewhere that the traces running under the GPS unit (and more importantly, its antenna). However, I didn't get any improvement when I removed the GPS from the board and ran wires from it to the board traces. I did redesign the board so that the GPS pads are on the other side, so the traces do not go under the GPS, but I don't think that's the issue.

Yes, I know, here's where you do a facepalm and ask "what in the world was he thinking?". I'm new to board design, and apparently moving into the difficult part of the learning curve.