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Tips and questions relating to the GPS modules from SFE
By zzpza
#52371
Hi,

Firstly, sorry if this is a repost. I tried to post this query this morning, but fell foul of the anti-spam restrictions.

I have a USGlobalSat EM-402 GPS module that I have connected to an Arduino Wee. I need to use the SoftwareSerial port to connect to the GPS as a datalogger is attached to the HW serial port to log sensor output, including the NMEA sentences from the GPS. Therefore the datalogger is everything the GPS says, plus extra data, so I thought it best to have this on the UART.

Anyway.... The GPS churns out soooo much data that it's overwhelming the little Arduino. I get 90% garbage when I monitor the UART from the PC. I do get the odd fully formed NMEA sentence, but it is not the norm. So, I would like to reduce the rate the GPS writes the different NMEA sentences to it's port. But, the GPS is ignoring me. :( I though it might be that I have got the checksum incorrect on my commands, so I tried to turn on debugging (as this would show such an error) but I can't get it into debug mode either. :( :( :(

This is the command I'm using to try to get into debug mode:

$PSRF105,1*3E

I got it out of the datasheet, so the checksum should be correct. I've tried sending it from the Arduino. I've also tried connecting the GPS (via the TTL to Serial-over-USB FT232R board) to my PC and used minicom on linux and hyperterminal on windows to send the command, all to no avail.

What am I doing wrong? :(

Any help would be very gratefully received! :)
Jules.
By no first name supplied
#52372
I've not used the Arduino, so these are general comments:

* Software serial TX is easier than RX. So consider swapping the GPS and the datalogger, i.e. have the logger on the soft port and the GPS on the UART.

* If you can run the datalogger at 4800 baud, and you don't need to receive anything from the logger, consider running them both on the UART - put the datalogger on the UART TX pin and the GPS on the RX pin. I have done exactly this on a PIC with a GPS and a radio modem, and it worked a lot better than my previous attempt to use a software serial port.
By zzpza
#52375
no first name supplied wrote:If you can run the datalogger at 4800 baud, and you don't need to receive anything from the logger, consider running them both on the UART - put the datalogger on the UART TX pin and the GPS on the RX pin.
you might just possibly be a genius!!!! :D