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

[tasmod]

Complete working prototype system



Rockwell GPS Module on right. PLL and TCXO board on left. TCXO is small vertical board top left. Small board at top with all wires is 7805 5v reg board.



Rear of LCD showing piggyback decoder.

[tasmod]

Darrel,

Don't know if you are still reading this thread.

I wondered how difficult it would be to add the final two numerical digits of the locator so that it is the full 8 digit string.

I nearly destroyed the prototype when I took it out in the car to test the locator code. The car voltage meant the regulator board became really hot, I was afraid it would fail.

Thanks,

[Darrel Taylor]

The code was based on the pearl script on the Wikipedia page, which only shows how to get 6 digits.

Do you know of somewhere that shows how to get the last two digits?

[tasmod]

Surprisingly I do have it in asm if that helps. I think this is the applicable code after GPS string is parsed. Loc 1 to 8 are the Maidenhead.

I wanted it all in PBP so I could do what I wanted to achieve. The final two are numeric digits. Mine is 03 if that helps re the original code.

;'''''''''''''''  Process LONG term '''''''''''''''''''''''''''''''''
    bcf     STATUS, C
    rrf     LongD           ;Easiest to work with LongD/2 everywhere
    btfss   STATUS, C       ;  as Loc works on 2 deg intervals
    goto    NoLongMinsUpdate    
                            
    movlw   LOW(d'6000')    ;Add 1 degree's worth of carry into the 
    addwf   LongMLo         ;   minutes registers if LongD/2 has a carry
    btfsc   STATUS, C
    incf    LongMHi
    movlw   HIGH(d'6000')   ;LongM in range 0 -  12000
    addwf   LongMHi
NoLongMinsUpdate            ;LongD' now in range 0 - 90
    btfss   NEGLONG
    goto    PosLong
    comf    LongD
    incf    LongD           ;LongD' now in 2's complement +/-90
    
    movf    LongMLo, w      ;Normalise LongM = 12000 - LongM
    sublw   LOW(d'12000')
    movwf   LongMLo         ;if borrow, C = 0, so increment the subtrahend 
    btfss   STATUS, C
    incf    LongMHi
    movf    LongMHi, w
    sublw   HIGH(d'12000')
    movwf   LongMHi

    decf    LongD           ;Correct Degrees

PosLong
    movlw   d'90'
    addwf   LongD           ;Normalise D' to 0-180
    movf    LongD, w
    movwf   ALo
    clrf    AHi

    movlw   d'10'
    call    DivMod          ;Mod out in A, Div out in B
    movf    BLo, W
    addlw   "A"
    movwf   Loc1
    movf    ALo, w
    addlw   "0"
    movwf   Loc3

    rrf     LongMHi         ;Divide by 4 to give range 0 - 2999
    rrf     LongMLo
    rrf     LongMHi
    rrf     LongMLo
    movlw   0x3F
    andwf   LongMHi

    movf    LongMLo, w      ;Mins * 100 / 4  DIV 125
    movwf   ALo
    movf    LongMHi, w
    movwf   AHi
    movlw   d'125'
    call    DivMod          ;Mod out in A, Div out in B
    movf    BLo, w
    addlw   "A"
    movwf   Loc5

          ;Recover  MOD term (scaled 0 - 124) which stays in ALo
    clrf    AHi
    bcf     STATUS, C
    rlf     ALo             ;Scale to 0 - 248
    movlw   d'25'
    call    DivMod          ;Mod out in A, Div out in B
    movf    BLo, w
    addlw   "0"
    movwf   Loc7	;Result in LongD, LongMHi, LongMLo , NEGLONG


            ;'''''''''''''''''''Now DO LAT term , LatD is already in range 0 - 90''''''''''''''''''
    btfss   NEGLAT
    goto    PosLat
    comf    LatD
    incf    LatD            ;LatD now in 2's complement +/-90

    movf    LatMLo, w       ;Normalise LatM = 6000 - LatM
    sublw   LOW(d'6000')
    movwf   LatMLo   
    btfss   STATUS, C       ;if borrow, C = 0, so increment the subtrahend 
    incf    LatMHi
    movf    LatMHi, w
    sublw   HIGH(d'6000')
    movwf   LatMHi

    decf    LatD            ;Correct the degrees

PosLat
    movlw   d'90'
    addwf   LatD            ;Normalise to 0-180
    movf    LatD, w
    movwf   ALo
    clrf    AHi

    movlw   d'10'
    call    DivMod          ;Mod out in A, Div out in B
    movf    BLo, W
    addlw   "A"
    movwf   Loc2
    movf    ALo, w
    addlw   "0"
    movwf   Loc4

    bcf     STATUS, C
    rrf     LatMHi          ;Divide by 2 to give range 0 - 2999
    rrf     LatMLo

    movf    LatMLo, w       ;Mins * 100 / 2  DIV 125
    movwf   ALo
    movf    LatMHi, w
    movwf   AHi
    movlw   d'125'
    call    DivMod          ;Mod out in A, Div out in B
    movf    BLo, w
    addlw   "A"
    movwf   Loc6		

          ;Recover  MOD term (scaled 0 - 124) which stays in ALo
    clrf    AHi
    bcf     STATUS, C
    rlf     ALo             ;Scale to 0 - 248
    movlw   d'25'
    call    DivMod
    movf    BLo, w
    addlw   "0"
    movwf   Loc8	;Result in LatD, LatMHi, LatMLo , NEGLAT


ShowLoc
    movf    Loc1, W
    call    LcdData
    movf    Loc2, W
    call    LcdData
    movf    Loc3, W
    call    LcdData
    movf    Loc4, W
    call    LcdData
    movf    Loc5, W
    call    LcdData
    movf    Loc6, W
    call    LcdData
    movf    Loc7, W
    call    LcdData
    movf    Loc8, W
    call    LcdData
  

    return

[tasmod]

I have made a separate switchable sub for the Big Digit clock which just uses the h, m, s, part of the gps string called alone.

Pic of result. As near accurate to second as code allows.

[tasmod]

Darrel,

I found this regarding the 4th pair.

THIRD PAIR (aa-xx)
Each field can be further divided into (24) 5 minutes (0.083333 degrees) longitudinal
by (24) 2.5 minute (0.0416665 degrees) latitudinal zones.

The first character encodes the longitude and the second encodes the latitude with
letters “a” thru “x” (refer to example 3 below).

Example 3:
Longitude = 0.338038 {Refer to example 2}
= 0.338038 / 0.083333
= 4 remainder 0.004706
= e
(location in 5th zone)
Latitude = 0.664048
= 0.664048 / 0.0416665
= 15 remainder 0.0390505
= p
(location in 16th zone)

FOURTH PAIR (00-99)
Each field can be further subdivided into (10) 30 seconds (0.008333 degrees) longitudinal
by (10) 15 seconds (0.004166) latitudinal zones. The first character encodes the longitude
and the second encodes the latitude with numbers “0” thru “9” (refer to example 4 below).

Example 4:
Longitude = 0.004706 {Refer to example 3}
= 0.004706 / 0.008333
= 0 remainder 0.004706
= 0
(location in 1st zone)
Latitude = 0.0390505 {Refer to example 3}
= 0.0390505 / 0.004166
= 9 remainder 0.001556
= 9
(location in 10th zone)

[Darrel Taylor]

Thanks Rob, that is helpful.
But the routines from the pearl script don't leave the variables in the right state to do the last part.

I'm trying to recreate it in a spreadsheet to see what values the variables should have at that point.
But finding time to look at it is difficult right now.

Just wanted to let you know I'm still working on it.