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

David J Taylor david-taylor at blueyonder.co.uk.invalid
Mon Apr 19 14:06:56 UTC 2010

"Terje Mathisen" <""> wrote in message news:ugut97-uqv2.ln1 at ntp.tmsw.no...
> It would still be limited to the resolution of the rs232 clock, i.e. 
> ~1ms, instead of the ~1us we usually get from PPS receivers.
> OTOH, for many users 1-3 ms might be just fine, and statistical 
> processing might make it stable at the sub-ms level, but with unknown 
> absolute offset.
> Terje

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....


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