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GPS connected to a PIC24F is haunted - need help

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razvanel

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GPS is haunted

yea that's right.

once in a while, recently more often unfortunately, my GPS connected to a PIC24F development board gives a weird sentence. connection is rs232 using the explorer 16.

normally it should be of the form:

$GPRMC,032952,V,2503.7186,N,12138.4145,E,,,250208,003.5,W*76

and instead i get some variance of:

$FPRLB, ..etc

and the format is consistent, characters are normal, english characters but there is no meaning to it.

what could be the problem??? please, please throw some ideas here cuz i am going insane...
 

GPS is haunted

From the example characters of the errors, it appears to be a single bit error. Usually this is caused by either a poor ground connection, a signal level issue, or using a RS232 hack rather than a real transceiver chip.
Scope the RS232 levels out of the GPS, are they good true RS232 levels? Many modern devices only drive to +-3V rather than +-12V which is the spec.
Does the PIC dev board use an RS232 tranceiver or just a resistor and a diode with bit-banged RS232?

To check for connection or grounding issues, get it working and then tap on the cable and connectors with a pencil. If the data gets corrupted, then you have a clue.
 

GPS is haunted

thanks i will give that a try. the gps is made by garmin and it has a 232 chip inside i suppose. i trust they have a good conversion going on. it's a +/- 5V so should be good. i will try the tapping method though. thanks..
 

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