[ntp:questions] How to debug GPS PPS?

David Lord snews at lordynet.org
Sun Feb 14 23:07:12 UTC 2010


David Lord wrote:

> What sentences is it sending NMEA or binary?
> 
> How do you have the unit wired to the serial port?
> The JST has pins 1-12 1=TxD2 2=RxD2 3=PPS 4=TxD1 5=TxD2
> 6=PD 7=AuxBat 8=GND 9/10=3.6 to 6V 11=nc 12=NMEA-out(cmos)
> 
> You need to check on below, it's best I can work out
> 
> ie JSTpin      D9pin
>      3 --------- 1
>      4 --------- 2
>      5 --------- 3
>      8 ---+----- 5
>           |
>           +---- 0V
>     10 -------- +3.6 to +6V
> 
> CMOS generated RS232 levels should be ok but depends on
> serial port of your pc. PPS out to DCD is given as 700mVp-p
> into 50r so will need converting to rs232.
> 
>> Tried to send  a message to change to 9600, and turn PPS on.
>> Ignored messages because of improper syntax.  Needs
>> proper checksum.
> 
> I have a gwbasic program for working out required messages.
> GPSD will do it for you. Garmin site also have a windows
> utility for generating required commands with checksum.
> 
> 
>>
>> Does anyone know of software that actually works with this
>> unit?
> 
> GPSD?

Going back to your previous reply I can see NMEA driver
looks to be working ok and you just need to trim out
the offset. GPSD + SHM driver might work ok for this
without PPS to give you about 10ms offset or with PPS
any of GPSD + SHM, NMEA or NMEA + ATOM should get you
in low us range for offset.

David




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