Parallax GPS Receiver

[emavil]

Hi,

I've read in the August/October 2008 issue, page 76, the GPS Receiver based from the Parallax GPS. I am fascinated with this project hoping to successfully build one. Parallax has a sample BS2 code for the GPS. I'm using PIC16F628A running at 10MHz xtal.

My problem is how to migrate the BS2 code to PICBasic Pro
Is there somebody who has a "basic" PICBasic code that enables PIC16F628A display the $GPRMC data on the LCD using Parallax GPS?


http://www.parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/txtSearch/gps/List/1/ProductID/396/Default.aspx?SortField=ProductName%2cProductName

The code is found in "GPS Reciever Manual v1.1 (.pdf)"

[ScaleRobotics]

I looked over the code just briefly. It has been a really really long time since I used a basic stamp. In my opinion, I would consider using the more powerful PIC16f628a without the basic stamp like commands. I do something a little different with a gps application, but most people use a command like:



gpsdata VAR BYTE[70] 'define a 70 character string gpsdata

HSerin 200, Main, [WAIT("$GPRMC"),STR gpsdata\MAXDATA\13] 'wait 200ms for GPRMC


Then you can look at each character of the string as gpsdata[x], gpsdata[0] will be the comma directly after GPRMC Saving it as a string is the way to go, the uart makes this pretty easy.


here is an example of pulling the latitude high numbers out of the sentence


IF gpsdata[13] = "A" Then 'tells you if valid data A= valid V=invalid
lathome_hi = ((gpsdata[15] - 48) *10)+((gpsdata[16] - 48)) 'first two digits
more code here.....
ENDIF

You will notice that I am subtracting 48, this is because I am changing an asci number to a decimal number for some math functions. You wouldnt need to do that if you are just printing to an lcd. But if you wanted to use the data for a project, you would need to convert to decimal. I don't know if you have already purchased it or not, but sparkfun.com has some too.

http://www.sparkfun.com/commerce/product_info.php?products_id=8975 but with this one you have to worry about 3.3 volt to 5 volt conversion.

[ScaleRobotics]

Here are some better examples:

http://www.picbasic.co.uk/forum/showthread.php?t=3805&highlight=16f88+device

[emavil]

thank very much scalerobotics, i'm not yet to this hardware UART thing. But the solution that you gave was a great help.

I consulted parallax's forum and the guy pointed out the i'm having problems with the baud rate.

Here's what i've sent to him.-----------------------------------------------------------------
We constructed the controller circuit last week. We followed what was written in the sample code
http://www.parallax.com/Portals/0/Downloads/docs/prod/acc/GPSManualV1.1.pdf

Upon testing the GPS receiver behaved the way it was described in the GPSManual. We modified the code based on our needs and we ended up having a message on the LCD some sort of "No Valid Data" or "No Response".

We are using PIC16F628A running at 10MHz crystal. We have peripherals such as RS-485 chip & a 4-liner LCD. We are using PICBasic Pro.

I've read also in the ELEKTOR magazine August/October 2008 issue, page 76, the GPS Receiver based from the Parallax GPS. The sad thing about it is that it is coded in C.

http://www.elektor.com/magazines/2008/july-047-august/gps-receiver.531567.lynkx

The sample code of Parallax is not working with our setup. Is there anybody who has a "basic" PICBasic code that enables PIC16F628A display the $GPRMC data on the LCD?

Here's my sample code in PICBasic version:
@ DEVICE PIC16F628A, HS_OSC '10MHz Oscillator
@ DEVICE PIC16F628A, MCLR_OFF '
@ DEVICE PIC16F628A, WDT_ON 'Watchdog Timer
@ DEVICE PIC16F628A, PWRT_ON 'Power-On Timer
@ DEVICE PIC16F628A, BOD_ON 'Brown-Out Detect
@ DEVICE PIC16F628A, LVP_OFF 'Low-Voltage Programming
@ DEVICE PIC16F628A, CPD_OFF 'Data Memory Code Protect
@ DEVICE PIC16F628A, PROTECT_OFF 'Program Code Protection

define OSC 10

DEFINE LCD_DREG PORTB 'Set LCD Data port
DEFINE LCD_DBIT 4 'Set starting Data bit (0 or 4) if 4-bit bus
DEFINE LCD_RSREG PORTA 'Set LCD Register Select port
DEFINE LCD_RSBIT 1 'Set LCD Register Select bit
DEFINE LCD_EREG PORTA 'Set LCD Enable port
DEFINE LCD_EBIT 0 'Set LCD Enable bit
DEFINE LCD_BITS 4 'Set LCD bus size (4 or 8 bits)
DEFINE LCD_LINES 4 'Set number of lines on LCD
'DEFINE LCD_COMMANDUS 4000 'Set command delay time in us
'DEFINE LCD_DATAUS 100 'Set data delay time in us

Symbol SIO = PortA.3 'Pin 2 of PICMicro connects to GPS Module SIO pin
TrisA = 0
TrisB = 0
CMCON = 7
' -----[ Constants ]-------------------------------------------------------
T4800 CON 188
Open CON $8000
Baud CON Open | T4800 ' Open mode to allow daisy chaining
TimeOut CON 6000
MoveTo CON 2 ' DEBUG positioning command
ClrRt CON 11 ' clear line right of cursor
FieldLen CON 22 ' length of debug text
EST CON -5 ' Eastern Standard Time
CST CON -6 ' Central Standard Time
MST CON -7 ' Mountain Standard Time
PST CON -8 ' Pacific Standard Time
EDT CON -4 ' Eastern Daylight Time
CDT CON -5 ' Central Daylight Time
MDT CON -6 ' Mountain Daylight Time
PDT CON -7 ' Pacific Daylight Time
UTCfix CON PST ' for San Diego, California
DegSym CON 176 ' degrees symbol for report
MinSym CON 39 ' minutes symbol
SecSym CON 34 ' seconds symbol
DLY con 500
' GPS Module Commands
GetInfo CON $00
GetValid CON $01
GetSats CON $02
GetTime CON $03
GetDate CON $04
GetLat CON $05
GetLong CON $06
GetAlt CON $07
GetSpeed CON $08
GetHead CON $09
' -----[ Variables ]-------------------------------------------------------
char VAR Byte
workVal VAR Word ' for numeric conversions
eeAddr VAR workVal ' pointer to EE data
ver_hw VAR Byte
ver_fw VAR Byte
valid VAR Byte ' signal valid? 0 = not valid, 1 = valid
sats VAR Byte ' number of satellites used in positioning calculations
tmHrs VAR Byte ' time fields
tmMins VAR Byte
tmSecs VAR Byte
day VAR Byte ' day of month, 1-31
month VAR Byte ' month, 1-12
year VAR Byte ' year, 00-99
degrees VAR Byte ' latitude/longitude degrees
minutes VAR Byte ' latitude/longitude minutes
minutesD VAR Word ' latitude/longitude decimal minutes
dir VAR Byte ' direction (latitude: 0 = N, 1 = S, longitude: 0 = E, 1 = W)
heading VAR Word ' heading in 0.1 degrees
alt VAR Word ' altitude in 0.1 meters
speed VAR Word ' speed in 0.1 knots
' -----[ EEPROM Data ]-----------------------------------------------------
NotValid DATA "NV", 0
IsValid DATA "V ", 0
DaysInMon DATA 31,28,31,30,31,30,31,31,30,31,30,31
MonNames DATA "JAN",0,"FEB",0,"MAR",0,"APR",0,"MAY",0,"JUN",0
DATA "JUL",0,"AUG",0,"SEP",0,"OCT",0,"NOV",0,"DEC",0
' -----[ Initialization ]--------------------------------------------------
Initialize:
PortA = 0
PortB = 0
PAUSE 250 ' let DEBUG open
lcdout $FE,$02,"<<GPS Receiver>>"
LCDOUT $FE,$C0,"SATs: Signal: "

Main:
GOSUB Get_Valid
GOSUB Get_Sats
GOSUB Get_TimeDate
GOTO Main

Get_Valid:
SEROUT2 Sio,Baud,["!GPS",GetValid]
SERIN2 Sio,Baud,TimeOut,No_Response,[valid]
if Valid = 0 then
lcdout $FE,$CE,"NV"
else
lcdout $FE,$CE," V"
endif
RETURN
' ----------------------------------------------------
Get_Sats:
SEROUT2 Sio,Baud,["!GPS",GetSats]
SERIN2 Sio,Baud,TimeOut,No_Response,[sats]
lcdout $FE,$C5,dec Sats
RETURN
' ----------------------------------------------------
Get_TimeDate:
SEROUT2 Sio,Baud,["!GPS",GetTime]
SERIN2 Sio,Baud,TimeOut,No_Response,[tmHrs,tmMins,tmSecs]
SEROUT2 Sio,Baud,["!GPS",GetDate]
SERIN2 Sio,Baud,TimeOut,No_Response,[day,month,year]
GOSUB Correct_Local_Time_Date
lcdout $FE,$90,DEC2 tmHrs, ":", DEC2 tmMins, ":", DEC2 tmSecs
LCDout $FE,$D0,DEC2 day,"-",DEC2 Month,", 20",DEC2 Year
RETURN

No_Response:
lcdout $FE,$CE,"NR"
PAUSE 1000
GOTO Main
' ----------------------------------------------------
Signal_Not_Valid:
LCDOUT $FE,$90," "
lcdout $FE,$D0," "
GOTO Main
' ----------------------------------------------------
' adjust date for local position
Correct_Local_Time_Date:
workVal = tmHrs + UTCfix
IF (workVal < 24) THEN Adjust_Time
workVal = UTCfix
BRANCH workVal.BIT15,[Location_Leads,Location_Lags]
Location_Leads:
day = day + 1
eeAddr = DaysInMon * (month - 1)
READ eeAddr, char
IF (day <= char) THEN Adjust_Time
month = month + 1
day = 1
IF (month < 13) THEN Adjust_Time
month = 1
year = year + 1 // 100
GOTO Adjust_Time
Location_Lags:
day = day - 1
IF (day > 0) THEN Adjust_Time
month = month - 1
IF (month > 0) THEN Adjust_Time
month = 1
eeAddr = DaysInMon * (month - 1)
READ eeAddr, day
year = year + 99 // 100
Adjust_Time:
tmHrs = tmHrs + (24 + UTCfix) // 24
RETURN
' ----------------------------------------------------
' Print Zero-terminated string stored in EEPROM
' -- eeAddr - starting character of string
Print_Z_String:
READ eeAddr, char ' get char from EE
IF (char = 0) THEN Print_Z_String_Done ' if zero, we're done
eeAddr = eeAddr + 1 ' point to the next one
GOTO Print_Z_String
Print_Z_String_Done:
RETURN

-------------------------------------------------------------------------

He answered

Okay, the issue is with how you are having the PIC communicate with the GPS. I've never worked with the PIC line before (or the various compilers), but I assume that you cannot just cut and paste the sample code that parallax provides for the BS2. The BS2 uses a PIC, but it's been transformed into something else. Anyway, it's probably a problem with the baud rate in the serout statements. I'd look in the manual for your PIC compiler and figure out what baud is needed.

The key bit of text in the datasheet for the GPS that you want to look at is the last line of 'Mode Selection' where it talks about the communication protocol. Figure out how to do that with the PIC, and that may solve your problem.

[ScaleRobotics]

I would use the code written for the same chip in post #6. Just change osc to 10, if that is what you are using, and either wire your lcd the same way, or edit those too.

http://www.picbasic.co.uk/forum/showpost.php?p=20518&postcount=6

Looks like he was printing other things to lcd, but you can easily use his examples.

It looks like the parallax gps accepts input, and can output specific data, but I would just use its standard NMEA output. This will output at 4800 baud NMEA, like almost all gps's on the market.