Quoting John Nelson:

This will be my last post tonight...I hope.
I think I understand the status register after some more thought. The only thing that concerns me is that the status register is now reporting "7F" or "8F". This would mean 7 or 8 satellites, but the "F" portion should mean the 3d Fix LED should be on, but it is not.
It would be helpful if your documentation mentioned details of using the I2C GPS with Mega Arduinos.
I like the speed of the I2C bus and the way you have parsed the NMEA sentences.
Finally, is the 1 PSS signal available?
Thank you,
John

Hi John,
Let me see if I can answer your questions. The 1PPS signal is not available externally. Originally when designing the board I thought about breaking out the signal but ran into the problem of deciding which pin to route it to. I started doing some research and noticed that I didn't see many people taking advantage of the 1PPS signal, which in hindsight I now know was probably not the best decision (I've received numerous requests about this). The signal is routed to the onboard controller so the firmware could be hacked using pin change interrupts to reroute the signal to one of the other header pins.

Oddly enough I didn't realize I left the section out of the the datasheet on how to modify the shield to make it usable with the Mega, but as you've seen it's only a matter of removing the two solder jumpers and soldering two wires to the Mega's I2C pins.

The 1ms delay you see in the code was due to intermittent strange behavior when requesting data from the shield. It seems to be a function of the AVR itself where there needs to be minimum delay of 4.7us between start and stop bits. Sometimes the setup time on the Arduino is below this value which is why I had the 1ms delay (actually if memory serves a simple 1 microsecond delay works also if you run into the problem).

As for the status register 0x7F and 0x8F you are seeing, yes the 7 and 8 are reporting the number of satellites used and the F is reflecting a 3D fix. In the case of this shield (another thing I failed to mention in the datasheet ) the led will shut off when there is a 3D fix and will blink when there is no satellite fix. You probably seen on other GPS devices an LED will light when there is a 3D fix and shut off when not. I actually did it opposite for power reasons (it uses less power to have it shut off in normal operation).

If you have any other questions please don't hesitate to ask.

Quoting Wutz:

Hi, I have a question regarding the I2C registers.

What happens when the speed exceeds the integer limit?
First I thought this will give just maximum integer value. But looking at the atoi definition, I think it will just skip the last digit, which would be the second decimal place.

The limit is 640km/h = 178 m/s, this is reachable and the GPS module is said to function until much more. Although it might be that you will lose satellite locking at those speeds.

You know what, you are correct. I went back and look to see what I did and I misread the datasheet as the maximum speed for the GPS IC as being 515 km/hr instead of the actual 515 m/s. So the number will probably rollover at 655 km/h.

Quoting jwangbb:

I purchased this GPS module and tried I2C_GPS_Sampe_S ketch_1_0. The reception is really poor. Only above to get a fix in clear sky condition. When I put it on the dash board of a car, and drived more than 10min (enough time even for downloading ephemeris) and still no fix, whereas my other GPS devices works no problem.

I have a few questions: 1) Is there a external ant port that I can use? 2) is there a way to display sensitivity of the device? 3) Is this device broken in any way?

What number is the status register reporting on the display?

Quoting jwangbb:

Wayne: I think I can get satellite's C/No info from NMEA Output Sentences $GPGSV to verify the sensitivity of the receiver. However, this seems to involve to modify the shields firmware. Could you please tell me is it the easiest way to go? And if so could you please tell me how to upload the code to shields mega rather than the Uno?

Actually the easiest way to compare sensitivities between receivers would be to look at the PDOP, HDOP and VDOP values (registers 0x19 - 0x1E). You should be able to compare these numbers across different GPS vendors also. There's a little write up about the parameters here ( gpsinformation.net/main/dopnontech.htm ) if u want to check it out but basically the lower the number the better with a 1 being the best possible accuracy.