How do I discern Maidenhead Locator from GPS lat long info.

[astanapane]

This weekend i will try to make some changes. I also found out that the NMEA sentence $GPVTG (from a chip MT3339) or $GNVTG (from a chip MT3333, with GLONASS) has the info of the speed in Km/h so it will be simpler to display speed at km/h.

[astanapane]

ok it is being some time since i made a change to the code. These days i l was trying to figure out how to embed the speed in my code. I left the part of the code with Days, Months, Years, on a side for a while.

Tomorrow i will upload the code with the speed embeded, and the limits at 10Km/h, 50Km/h, 100Km/h. I have placed for the indication of each limit some LEDs at A Port.

I have also noticed that code is expanding, and at the end i might need a bigger PIC chip.

[astanapane]

These days i tried to use the $GPVTG sentence and get the speed from there as it is in Km/h

First of all the format of the $GPVTG sentence is as follows.

1. X.XX for the left X before the "dot" when the speed is less than 10km/h
2. XX.XX for the XX before the "dot" when the speed is more than 9 km/h and less than 100km/h
2. XXX.XX for the XXX before the "dot" when the speed is more than 99km/h

For the .XX so the two digits after the "dots" those are the decimal part and stays stable in the $GPVTG sentence.

We need to check when the speed change, where is the dot.

serin2 gps_tx,84,timeout,lostcable,[wait("GPVTG"),wait("N"),_
wait(","),TS[0],TS[1],TS[2],TS[3],TS[4],_
wait(","),SKIP 3]

for i = 1 to 3
    if TS[i]="." then decimal = i   'TOTAL SPEED. find which character is the decimal point 
    next i

select case decimal 'if the gps shows 1.45 it may be 145
                    'for the conversion ASCII to number we can use the -48
    case    1       'decimal position is x.xx
        speed = (10*(TS[0]-48))+(TS[2]-48)
    case    2       'decimal position is xx.xx
        speed = (100*(TS[0]-48))+(10*(TS[1]-48))+(TS[3]-48)
    case    3       'decimal position is xxx.xx
        speed = (1000*(TS[0]-48))+(100*(TS[1]-48))+(10*(TS[2]-48))
    end select     
    
gosub OVERSPEED:


OVERSPEED: 

if SPEED > 1000 then     ' 100Km/h
    high porta.3
    low  porta.2
    low  porta.1    
else
    LOW porta.3
    
if SPEED > 500 then     ' 50Km/h
    high porta.2
    low  porta.1    
else
    LOW porta.2
    
if SPEED > 100  then    ' 10Km/h
    high porta.1
else
    LOW porta.1

endif
    endif
        endif
    return

At the moment the code is working as it is, but i think i need to change the multiplication of 10*, 100* and 1000*, to 1*, 10* and 100*, because as you see at the OVERSPEED: i use 1000 for the 100 km/h, 500 for the 50km/h and 100 for the 10km/h.
But then the dot will change place, or i will not being able to identify the right place of it. Anyhow the code is working for the speed.

Still i need to:

1. Make the Day/Month/Year to work properly, now i think i will not have a problem to solve this.

2. The display data are refreshed, my goal is to make the data stable all the time at the screen and change only the needed values.

[astanapane]

Could you tell me if it is a good choise continuing this project with PIC16f887 i/p?

[richard]

Could you tell me if it is a good choise continuing this project with PIC16f887

its basically the same very limited chip you are presently using with a few more pins.
if you are serious in wanting to calculate maidenhead then no its a poor choice.
at least get something like 16f18326 ,16f18875 or better still a pic18 chip
I like pic18f26k42 [if you have pbp3.1] or a pic18f26k22 with pbp3.0 for this sort of project

[astanapane]

Hi Richard,

thanks a lot again for your reply. I'm trying to use a chip that i can program with pickit2 as i dont want to spend any money for the pickit 3.

I'm planning to purchase the PBP3.1 software, than spend for pickit3 hardware. Im happy with pickit 2, and a close supported device as far as i see is the pic18f26k20.

At the moment in stock i have the pic18f4550, pic16f1939. What is the feature of the pic we are looking for. The CPU SPEED (8bit or 16bit...), the SRAM, timers?

[richard]

What is the feature of the pic we are looking for. The CPU SPEED (8bit or 16bit...), the SRAM, timers?

its not my project I don't know what you have planned but generally speaking if you are dealing with parsing strings from a serial stream , more sram is better ,the possibility of more speed is always better. make sure there is plenty of flash space to hold the program. if its a one off project get the best chip with enough pins and features required .
if you are going to do large amounts of and/or complex math then pic18's with a hardware multiplier can increase speed and
reduce code size

pk2 will program 18fk22 series , once you have used a chip with pps there is no going back. the k42 series chips leave the others in the dust