# Garbage reading GPS **URL:** \ **Category:** Rabbit\ **Created:** [June 1, 2007, 6:21am UTC](https://forums.digi.com/t/garbage-reading-gps/9090 "2007-06-01T06:21:44Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![xcesmess](https://avatars.discourse-cdn.com/v4/letter/x/c6cbf5/32.png) [@xcesmess](https://forums.digi.com/u/xcesmess)\ **Post date:** [June 1, 2007, 6:21am UTC](https://forums.digi.com/t/garbage-reading-gps/9090/1 "2007-06-01T06:21:44Z")
I finally got my GPS unit in but I’m having a heck of a time getting it to connect. It is a Garmin GPS15 and has 0-3.3v CMOS serial output (two wire). I’m using a 3100 on the prototype board and I’ve tried hooking it up to RxC/TxC on J5 and then I’ve also hooked it up to PC2/PC3 on the headers but all I typically get is garbage when I manually read the port (not even sure I’m doing that right!) I’ve tried the sample GPS application and all I get is the sample distance (LA to whatever) and then it just sits. The GPS is running at 4800bps fixed. The datasheet on the GPS is here: [http://www8.garmin.com/manuals/GPS15\_TechnicalSpecification.pdf](http://www8.garmin.com/manuals/GPS15_TechnicalSpecification.pdf) Any help would be appreciated! Thanks! Kelly Koehn ---
**Author:** ![xcesmess](https://avatars.discourse-cdn.com/v4/letter/x/c6cbf5/32.png) [@xcesmess](https://forums.digi.com/u/xcesmess)\ **Post date:** [June 2, 2007, 2:35am UTC](https://forums.digi.com/t/garbage-reading-gps/9090/2 "2007-06-02T02:35:55Z")
Well I’ve decided to contact support on this issue. I’ve been working with some folks on the Yahoo Rabbit group with no success. However I have done some testing here on my own. I have verified the GPS is working. I built a CMOS to RS-232 converter and hooked it up to my laptop. I am able to read the ASCII output from the GPS. I’m suspecting that I’ve got a possible prototyping board problem as I can switch core modules out (I have a 3100 and 3110 both) and both units mimic the same problem (scrambled ascii output). I’ve switched the ports to port B and C (Rx obviously) and still receive nothing but scrambled text. What is the likelihood that the serial port(s) on this board could be toast? I’ll attach a copy of my code to the bottom of this. It is merely just the GPS\_SAMPLE program with a small printf command to show me the raw data coming in. Any help or advice would be appreciated… starting to get desperate here! Thanks Kelly Here is a small sample of what the Rabbit gives me in STDIO: ����y��q\_qYS��������������������������������������������������������������[u�� ��e��e��\_e�Y���}���������������������������\_q������������Q��������������q\_qY}�} ������������������������������������������y��q\_qYS������������������������������ Here is a sample of what SHOULD be giving: $GPRMC,012616,A,3747.8016,N,09718.3226,W,0.0,20.2,020607,5.0,E\*5A $GPGGA,012616,3747.8016,N,09718.3226,W,1,05,2.1,427.3,M,-27.0,M,_74 $GPGSA,A,3,03,10,13,16,27,2.3,2.1,1.0_33 Here is the code that I’m using on the Rabbit: #class auto #use “gps.lib” #define BINBUFSIZE 127 #define BOUTBUFSIZE 127 #define MAX\_SENTENCE 100 // names of days of week const char dayname[7][4] = {“Sun”,“Mon”,“Tue”,“Wed”,“Thu”,“Fri”,“Sat”}; const char monthname[12][4] = {“Jan”, “Feb”, “Mar”, “Apr”, “May”, “Jun”, “Jul”, “Aug”, “Sep”, “Oct”, “Nov”, “Dec”}; GPSPosition current\_pos; struct tm current\_time; void main() { char sentence[MAX\_SENTENCE]; int input\_char; int string\_pos; char dir\_string[2]; ``` //calculate distance from known coordinates GPSPosition la_loc, sf_loc; la_loc.lat_degrees = 34; la_loc.lat_minutes = 00.0; la_loc.lat_direction = 'N'; la_loc.lon_degrees = 118; la_loc.lon_minutes = 15.0; la_loc.lon_direction = 'W'; sf_loc.lat_degrees = 37; sf_loc.lat_minutes = 45.0; sf_loc.lat_direction = 'N'; sf_loc.lon_degrees = 122; sf_loc.lon_minutes = 27.0; sf_loc.lon_direction = 'W'; serBopen(9600); string_pos = 0; dir_string[1] = 0; //printf("SF to LA:%f km ``` ", gps\_ground\_distance(&sf\_loc, &la\_loc)); ``` //receive and parse GPS data while(1) { input_char = serBgetc(); printf("%c", input_char); if(input_char == '\r' || input_char == ' ``` ‘) { sentence[string\_pos] = 0; //add null printf("%s ", sentence); if(gps\_get\_position(¤t\_pos, sentence) == 0) { dir\_string[0] = current\_pos.lat\_direction; printf("Latitude: %d %f’ %s ", current\_pos.lat\_degrees, current\_pos.lat\_minutes, dir\_string); dir\_string[0] = current\_pos.lon\_direction; printf("Longitude: %d %f’ %s ", current\_pos.lon\_degrees, current\_pos.lon\_minutes, dir\_string); ``` } if(gps_get_utc(&current_time, sentence) == 0) { printf("UTC: %s %d-%s-%d %02d:%02d:%02d ``` ", dayname[current\_time.tm\_wday], current\_time.tm\_mday, monthname[current\_time.tm\_mon - 1], 1900 + current\_time.tm\_year, current\_time.tm\_hour, current\_time.tm\_min, current\_time.tm\_sec ); } string\_pos = 0; } else if(input\_char \> 0) { sentence[string\_pos] = input\_char; string\_pos++; if(string\_pos == MAX\_SENTENCE) string\_pos = 0; //reset string if too large } } } ---
**Author:** ![xcesmess](https://avatars.discourse-cdn.com/v4/letter/x/c6cbf5/32.png) [@xcesmess](https://forums.digi.com/u/xcesmess)\ **Post date:** [June 2, 2007, 5:56am UTC](https://forums.digi.com/t/garbage-reading-gps/9090/3 "2007-06-02T05:56:12Z")
Well I’ve discovered the mystery to why reading a GPS was such a hassle… and possibly why my PWM’s quit functioning. Something on teh prototyping board has went awry. I took the core off the board and only used the voltage regulators on the board… hooking all my jumpers directly to the core… and everything works flawlessly. I can read text from the GPS, motor controllers work… just like it should. I wonder if anyone else has experienced this kind of failure on the 3x series board… I guess a call to the reseller and/or manufacturer is on the way… Kelly