[ntp:questions] Cheap ($29.90) GPS receiver

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Mon Apr 19 17:29:32 UTC 2010

>How precise can a 4800 baud serial port be in determining the start of a 
>start bit?  About 1/4800s i.e. about 200 microseconds?  Don't the chips 
>sample at 8 or 16 times baud rate, so couldn't the start bit be determined 
>to ~25-30 microseconds?  And if the baud rate was lot higher (the unit 
>claims 57600 baud)?
>You would be using the unit in a slightly different mode to an existing 
>GPS - just detecting the start of an RS-232 burst for the PPS, and then 
>reading a message for the actual value....

What you describe could be made to work quite well, but I've never
seen one that works that way.

The data sheet says 1 microsecond.  It also says SiRF chip set.
All the SiRF units that I've tested are horrible.  They aren't even
trying for good timing.

My guess is that the 1 microsecond was copied from another data
sheet that did have a PPS signal.

If anybody tests one of these, please let us know how well it works.

These are my opinions, not necessarily my employer's.  I hate spam.

More information about the questions mailing list