Gps With Picaxe

[Lachlanmiller]

Im building quite a complex clock, and thought i might as well include a gps chip in it, to keep the time correct.

there are many many many choices of gps modules, just trying to find out the right one.

The EM-406A seems a popular choice. but wants the difference between it and the EM-408 or the EM-411 ????

also, if i connect vcc and gnd, will gps data start streaming out the serial pin, or does it need to be initialized?

thanks
lachlan

 

[eclectic]

Could you post links to datasheets please?

e

 

[papaof2]

also, if i connect vcc and gnd, will gps data start streaming out the serial pin, or does it need to be initialized?

The data will *usually* start streaming out, but there are some "gotcha's" -

A GPS needs to "see" the sky - it won't work through multiple layers of house above you. If your clock is two floors below the roof, the GPS may never acquire lock.

The EM406 default serial speed is 4800 baud. You can change this with a command.
It defaults to sending multiple messages (RMC, GGA, GGL, etc). You only need one message type to get the date/time, so you may want to turn off the other messages. See the user guide for the content of the various messages and how to turn them on/off.

I've tested a couple of EM406 units and they acquire lock inside the house in a couple of minutes from a very cold start (in the box for who knows how long). Note that this is a brick house and there is a floor above my work area; however, the GPS is next to a large [6 ft by 5 ft] south-facing window.

The EM406 has a super-cap that holds "last position" information for about 12 hours.

The GlobalSat page on the EM406 is here http://www.usglobalsat.com/p-46-em-406a-sirf-iii.aspx and you can download the user guide there.

GlobalSat also sells "re-certified" GPS units. The EM406A is $20US plus $10 for shipping in the US. http://www.usglobalsat.com/p-641-81-em-406a-sirf-iii.aspx I have one of these and so far it works just as well as the one I bought new.

John