Any hints from the firmware that could make a software GP-E2 clone?

[ryebrye]

I'm interested in automatically geotagging, but less interested in spending $250 for a GPS unit with a USB connection. Does the GP-E2 do USB host or does the camera?

If the camera is the USB host, making something that would emulate the GP-E2 and send GPS info to the camera would be pretty easy - I have more than a few older android phones with good GPS receivers in them and functioning USB ports that I could use...

Or perhaps building an arduino-based alternative to the GP-E2 would be another idea.

Anyone know where in the firmware it shows the protocol used to talk to the GP-E2? 

[1%]

I don't think camera can do host.

[nanomad]

I think the GP-E2 uses PTP to talk to the camera so it's acting as a host

[ryebrye]

building an Arduino-based device that does PTP and has a GPS chip in it would be pretty easy - but the cost for a good GPS receiver + arduino etc would probably not make it super enticing unless you already had the parts from another project