LS20031 output issues?

GPS/GNSS Development Boards
1

I purchased this GPS unit http://www.sparkfun.com/products/8975. I am not able to get a readable NMEA sentence from the unit. I have it hooked through a Max232 breakout board to a computer serial port (actually a Serial to USB converter). From my reading, the device is supplied with a 57600 baud rate. I see what looks like the start of NMEA sentences coming off, but there are lots of extended ascii characters scrolling through (and now at the end). The red LED is flashing once a second, so it has a reasonable fix. I tried every baud rate possible as well as deviating from N-8-1. It all looks the same though - random characters. I sent command sequences to make sure the device was set for 57600 baud: $PMTK251,57600*27. Still no help.

Here’s what the output looks like:

http://public.tjb-home-backup.net/dixie … 323060.jpg

I know it’s got to be something reasonably simple, but I’m at a loss. Any ideas?

2

Looks like it’s garbled up from noise.

Slow down the baud rate. Try a 10K (maybe 4.7K or otherwise) pullup and/or pulldown on the RX line. Double-double check the ground between the GPS and USB/serial converter and laptop.

3

Try to change the Flow control from “none” to “hardware”.

4

juffyvega12590:
Try to change the Flow control from “none” to “hardware”.

Won't do anything. CTS/RTS not used by the GPS module.
5

You can’t send commands to set baud rate unless you know the baud rate it’s set to. The GPS will receive gibberish if, for example, it’s expecting 9600 and gets a command string at 57600.

Is your ground hooked up correctly?

Maybe recheck wiring and pinout too.

I don’t suppose you have an oscilloscope or logic analyzer? That might help you figure out what is going on a little better.

Michael

6

Folks,

Thanks for the replies… Sorry I was overtaxed with other things (and was working on other components of the overall package). Now, I’m back on this… So, I’m still getting gibberish. I’ve tried every baud rate. At the “factory” baud, I’m still getting this:

$GPÇGA,224407.19y,385v.378ôç¾þÿÿüþÿ<þ?¾ÿ<~ÿþ|?>?¿þ<>þþþþÿ¾?<<?ÿþþüÿþüþ¾þþÿþüþþ?þ¾þÿþ?|þüÿ>ÿÿÿ?ÿþÿÿ<ÿþÿÿø<ÿ?ÿ<üþþÿ¾ÿÿþ<ÿþþÿÿø>þÿ>þþ8þÿ¾þÿ¿?ÿ?ÿÿÿÿÿþø$GPGGA,224407n398,3852.33xp,N,÷~?ü¾~<ÿðÿþþÿÿ?ÿÿ¾~<ÿðþ?üÿþþÿþþ<ÿ>þþ?ÿðÿþüþþÿþ<ÿæþ<þþþþÆþÿÿ?ÿüÿþþüÿ?þ<þþüÿ<ÿÿüþþÿ>þþø<ÿ~þ?ðÿ<ÿÿÿþü¾þ<þ?þÿ$GPGGA,224407.598,s85r>s3?>,ïÿ÷þ¾þ¾?ÿþÿüþþ?üþüþþ?>ÿü?ÿÿ?ÿüÿ?üðþÿÿÇÿ>üÿÿþü?>ÿþþþü?ÿøþÿþÿþ??ÿþÿþÿÿÿÿÿ???þþþþþ~ÿþ?|þÿÿÿ>ÿ?ü<ÿ~þÿ<<ÿþþþðþþþÿ?ÿþÿÿþÿ<?ÿÿðÿÿÿþÿ<¿<ÿüøÿðþ$GPGOÁ,22440w.797,3x52.3373,Þlð??>ÿúþÿÿ<?þÿþ~ÿÿÿ>ÿÿüþþ>¾þÿ?ÿ>?ÿ~ÿ~ÿàþþþþÿþÿþÿ<ÿÿÿ>?þÿþ¾?ø<ÿþþü<|þÿþÿþ~~8ÿ>ÿÿÿ<øþøÿÿÿþþþ÷ÿ<<ÿþÿü¿þðÿ?þþüÿøþÿþÿþÿ¾ÿþÿÿÿø<~þþþÿüþþþÿ>~$GPGGA,224407.99u,3852.s36?|~¶ÿ>ÿ?<ÿæ~~?ÿ~?üþÿ?>>þ~ÿ>þþÿÿøÿÿ?þ><>>ÿÿ<?¾?þ>ÿ>þöþþ|þÿ~ÿ?ÿ0?ÿÿ?|ðüÿ?þÿÿÿþþ>þüÆÿÿÿþx?ÿ¾?ÿ<ÿ$GPGGA,224408.193,3852.3w~<þÿÿÿ<þÿ¿ÿþ<¿üÿ|ÿþ|þ¾?ÿ>þþþÿøÿðþ>þ<>>ÿ?<ÿþüþÿ~ÿ<ü¾þþ¾ü?þþ>ÿ?üþÿÿü<ÿÿ>þþþ0ÿÿÿþþÿþþÿþÿÿþ$GPGGA,224408.391,38=6>ó÷ÿ?øþÿÿþÿÿüþÿ>ÿ¿þÿÿü8>0þ~¾ÿþ8~þÿøÿþþ¾~|~üþÿ?>þ0ø<üÿþ?¾ÿ?ÿ>ÿÿ8ÿþþÿþþÿÿ~ÿ>þþ<üþþ?þ¾ÿü8ÿ??þ¾>ÿÿ?ÿÿ>ÿÿÿÿ>¿?þü??þ>þÿ>~þÿ>$GPGGA,224408.590,3852n37~¾ðÿ?ÿþüþÿþÿøÿü8þþ0ö~¾ÿþøÿÿ<<ÿ~ÿ<ÿ>>þð0þÿþÿ¾ÿÿøÿüü>ÿü<>þþÿ<ÿ>ÿ>>þÿ?ÿ~|~þüÿüø>þþþ¾þÿÿÿÿÿ8<þþüþ÷ÿþ<<üþÿ><$GPGGÁ,224408.789<3852n3w6<þÿ?ÿ?¾ÿ?ÿÿø8þðÿ?¾øÿÿ?<¾þðþ¾?<üÿøÿü?ü~>þþð0ÿÿþÿÿöÿÿ?þü<ÿþÿ>þÿÿÿ?þüÿþÆþüþøøÿÿÿ>þþ>þð?ÿÿ?ÿ?ÿÿÿþÿ>þ<þÿ<þÿþ$GPGGA,224408.987<3856.s®þÿ??>ÿÿÿü¾þÿüþ?>þ¿<üþþþ~<ÿ?ÿ?>ÿÿÿÿ><þ¾ÿÿ<ÿ?üÿþÿþÿ>ÿÿ8ÿþþ?þþÿ<ÿ¾þþ|~?þþ|~?þÿ?þþÿþþÿÿ??þüþ<þ<ÿþþþ<þþÿþ¾þÿ¾>ÿÿÿ>ÿ?ÿ??þðþÿÿ?öþüÿÿÿþüþ?ÿþø$GPGOÁ,224409.186,3852.s7¾ù<þ¾ÿþü?<ÿ??üþ<¿üÿÿ<¾ÿÿü<>?þpÿ?ÿ0ÿ>ÿ<ü¾ÿÿÿÿÿüöþ¾ÿ???þþþÿ?þüÿþ¿þüþ>þ?ÿ?ü><þÿÿüü|þþÿÿÿÿþÿ><ÿÿÿ<þ?ÿþþþ<þðÿÿÿÿ?ÿ$GPGÇA,224409.386,3852.7f÷ÿ??<ÿü>ÿÿð??ÿÿÿÿ¾8ÿðÿÿÿÿÿÿþþÿ<ÿ<þÿ>üþüÿ<>þþ?þÿÿþüøÿÿÿøÿÿ?þ>ÿ?ÿ<üÿ<þ<þüþþÿÿÿ<ÿ<|þþþþÿ?þÿ<ÿþþþ¾~8<?ÿþ?þþ¾þþð>þÿ?æþü<ÿÿ$GPGGA,224409.585,3852.s3üû~¾?ÿ<?0¿>ÿ<ÿøÿ?>>þð?<ÿ?þðÿðÿ0þ<ÿ<þþüîüÿüð<þþþ~>þÿÿÿ>ÿÿþþÿþÿ>þ?¾ÿþÿ>þÿ¾þþðþÿþþüþ~ÿÿü8ÿÿÿÿÿþ<þ¾ÿÿþð?þü>0üÿÿÿ?þüþ?ÿø$GPGGA,22<409.w85,s85r.33|úþ<ÿ|þïþþ<þÿþ<þüÿÿþ0ÿÿÿ<ÿÿÿðÿ<?þ<?þÿþÿöþ>þ~øÿüî÷ø~þöþÿÿþ?þüüþþþÿþþ;

There are some “starting” parts of an NMEA sentence ("$GPGGA, for instance), but there’s no reliable or other delimiters that are “standard” (separated by commas). I have two units and both seem to do this, so it’s unlikely that they’re defective (I guess). I’ve tried both pull up and pull down on the transmit line. I actually get the same stuff (pull up, pull down, no resistor). Any other possible suggestions? I’ve used both my compiler COM program and Tera Term.

7

I am seeing the same thing all of the sudden.

I bought the GPS module a few months ago, played around with and had it working fine. It took a long time to get a fix the first time (minutes) but then after it had the almanac or whatever it was able to get a new fix in 5 to 10 seconds. Then I shelved it for a couple of months to work on other things. Last night I hooked everything up again.

At first I was getting good NEMA sentences but was never able to get a GPS fix. I left it running over night. This morning I powered it off and back on and now all I get is really noisy data like the OP. I haven’t seen a valid NEMA sentence since.

I leaning towards thinking that these units either go bad after a few months or I zapped it with static electricity or something. If anyone has a fix, that’d be awesome.

8

Alright… total operator error here. Had a pin mixup and was only getting 3.3V to my max232 board. Supplied the correct voltage and it looks fine. Thanks for the help (and sorry to make such an error!).