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Tips and questions relating to the GPS modules from SFE
By adammhaile
#30770
So, I have a project I want to use the GPS Logger for. While continuous logging at an interval would technically work... I would have to go through later and filter out the entries I don't need. So only logging to the SD card when I tell it to (as in asynchronously) would be much more efficient.

Does anyone know how I could achieve this? Either through hacking the hardware or the firmware.

From the hardware schematic it looks like it would require overriding the signal input to XTAL1, XTAL2 and/or RTXC1, RTXC2 on the main chip. But to be honest...that's just a total guess, I really have no clue.

Any help would be greatly appreciated!
By pelesl
#32086
I think the 1Hz data rate is a consequence of the GPS system (satellites sending timing streams) rather than the devices themselves. I recently took a US Global Sat (a Taiwanese company, by the way) BT359W and connected to its bluetooth serial port via hyperterminal. As soon as the device is on, it's spitting out NMEA sentences. They are sent in groups, once per second; every three or four seconds it reports satellite lock info and the rest are position sentences (don't remember which specifically right now).

As far as I can tell, there is no way to send a position request. I don't know much about GPS, but if this commercial unit is constantly spitting sentences I doubt there's a way to request them specifically.

As far as asynchronous logging is concerned, this is exactly what cameras like the Nikon D200 do---with an NMEA-enabled GPS attached, they record position information in the photo's EXIF data. My guess is that the cleanest way to do it is to have a position buffer in firmware that is overwritten each second with the latest position sentence, and when the user requests an immediate "log", the firmware would dump this last sentence into the flash card or whatever.

You may want to talk to the people playing with the Nikons, they may know more about what the camera does. You can start here:

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