Menu
While APRS and AX.25 provide data integrity, my programming skills lacked the expertise to implement this method. So I started thinking about using the amateur radio standard AFSK RTTY at 170Hz shift. Data integrity should be maintained fairly accurate because the receiving station and payload will be in Line of Site with each other. The payload TM signal should be very strong at the receiving station(s).
Searching this site and using Google, I could only find a couple of articles in the PICAXE forum and none on this forum.
Reading the GPS NEMA 0183 data was simple, converting the $GPGGA NEMA string ASCII data into Baudot and readying it for transmit it was a bit trickier
Here is my prototype PIC RTTY Telemetry project:
http://www.n6vmo.com/PIC/SARCHAB7.zip
Code:
'************************************************* ***************
'* Name : SARCHAB7.BAS *
'* Author : [select VIEW...EDITOR OPTIONS] *
'* Notice : Copyright (c) 2011 [select VIEW...EDITOR OPTIONS] *
'* : All Rights Reserved *
'* Date : 6/17/2011 *
'* Version : 1.0 *
'* Notes : *
'* : *
'************************************************* ***************
'PICBASIC PRO program to read a 4800 BAUD GPS GPGGA/RMC NEMA
' 0183 string and transmit it using BAUDOT (RTTY) with standard amateur
' radio AFSK 170Hz shift, using the XR2206 modem and the PIC16F627.
'
'
INCLUDE "BS2DEFS.BAS"
DEFINE HSER_CLROERR 1 'USART CLEAR OVERFLOW ERROR
DEFINE HSER_TXSTA 24H 'SET USART TX STAUS REG
DEFINE HSER_RCSTA 90H 'SET USART RC STAUS REG
DEFINE HSER_BAUD 4800 'SET USART BAUD RATE
define HSER_SPBRG 50 'SET PIC OSC FOR 4800 BAUD
RXDATA VAR BYTE (50)
UTC VAR BYTE (10)
RMCUTC VAR BYTE (10)
LAT VAR BYTE (9)
RMCLAT VAR BYTE (9)
NS VAR BYTE (2)
RMCNS VAR BYTE (2)
EW VAR BYTE (2)
RMCEW VAR BYTE (2)
LNG VAR BYTE (10)
RMCLNG VAR BYTE (10)
ALT VAR BYTE (7)
FQ VAR BYTE (1)
SATS VAR BYTE (2)
HDP VAR BYTE (3)
SPD VAR BYTE (5)
TRK VAR BYTE (5)
PIR1 = $0C 'ASSIGN USART RX INTERUPT REG
PTT VAR PORTB.4 'ASSIGN PTT PIN
O Var PORTB.5 'ASSIGN BAUDOT OUTPUT PIN
CUT VAR PORTB.6 'ASSIGN CUTDOWN OUTPUT PIN
I VAR BYTE
L VAR BYTE
BAUDOTDATA VAR BYTE
BAUDOTBIT VAR BIT
BEACONCOUNT VAR BYTE
ADDRESS vAR WORD
ALTFT VAR WORD
FEET VAR WORD
SPDMPH VAR BYTE
MPH VAR BYTE
BEACONCOUNT = 1
'----------------------------------------------------------------
MAIN:
IF BEACONCOUNT = 5 THEN BEACONCOUNT = 1
GOSUB READGPS
GOSUB PUSHTOTALKON
GOSUB DISPLAYFORMAT
GOSUB METRICSAE
GOSUB TXGGARMCDATA
BEACONCOUNT = BEACONCOUNT + 1
IF BEACONCOUNT = 5 THEN GOSUB BEACON
IF BEACONCOUNT = 5 THEN GOSUB WEB
GOSUB PUSHTOTALKOFF
GOSUB CUTDWN
'PAUSE 60000 'PAUSE FOR 60 SECONDS BETWEEN TRANSMISSIONS
GOTO MAIN
'-----------------------Read GPGAA NEMA 0183 Data
READGPS:
'G G A ,
HSERIN [WAIT (71,71,65,44), STR UTC \6]
HSERIN [WAIT (44), STR LAT \9]
HSERIN [WAIT (44), STR NS \1]
HSERIN [WAIT (44), STR LNG \10]
HSERIN [WAIT (44), STR EW \1]
HSERIN [WAIT (44), STR FQ \1]
HSERIN [WAIT (44), STR SATS \2]
HSERIN [WAIT (44), STR HDP \3]
HSERIN [WAIT (44), STR ALT \6\44]
'------------------------Read GPRMC NEMA 0183 Data
'R M C ,
HSERIN [WAIT (82,77,67,44), STR RMCUTC \6]
HSERIN [WAIT (44), STR RMCLAT \9]
HSERIN [WAIT (44), STR RMCNS \1]
HSERIN [WAIT (44), STR RMCLNG \10]
HSERIN [WAIT (44), STR RMCEW \1]
HSERIN [WAIT (44), STR SPD \4]
HSERIN [WAIT (44), STR TRK \5]
RETURN
'--------------------------PTT OUTPUT-----------------------------
PUSHTOTALKON:
HIGH PTT
PAUSE 500
RETURN
'--------------------------PTT OUTPUT-----------------------------
PUSHTOTALKOFF:
LOW PTT
PAUSE 500
RETURN
'-------------------------FORMAT RX STATION-----------------------
DISPLAYFORMAT:
GOSUB LTR 'SEND LTR
FOR I = 0 TO 4
GOSUB TX
NEXT I
GOSUB FIG 'SEND FIGS
FOR I = 0 TO 4
GOSUB TX
NEXT I
GOSUB CRTN 'SEND CR
FOR I = 0 TO 1
GOSUB TX
NEXT I
GOSUB LF 'SEND LF
FOR I = 0 TO 1
GOSUB TX
NEXT I
RETURN
'-------------------------------------------------------------
TXGGARMCDATA:
'------------------UTC---------------------------
ADDRESS = $FB0 'UTC ADDRESS
FOR L = 0 TO 5
PEEKCODE ADDRESS, BAUDOTDATA
GOSUB TX
ADDRESS = ADDRESS + 1
NEXT L
FOR L = 0 TO 5 'MOVE UTC INTO RXDATA
RXDATA (L) = UTC (L)
GOSUB TRANSLATE 'TRANSLATE ASCII TO BAUDOT
GOSUB TX 'TRANSMIT BYTE
NEXT L
GOSUB CRTN
GOSUB TX
GOSUB LF
GOSUB TX
'------------------LAT------------------------------------------
ADDRESS = $F60 'LAT ADDRESS
FOR L = 0 TO 5
PEEKCODE ADDRESS, BAUDOTDATA
GOSUB TX
ADDRESS = ADDRESS + 1
NEXT L
FOR L = 0 TO 8 'MOVE LAT INTO RXDATA
RXDATA (L) = LAT (L)
GOSUB TRANSLATE 'TRANSLATE ASCII TO BAUDOT
GOSUB TX 'TRANSMIT BYTE
NEXT L
GOSUB CRTN
GOSUB TX
GOSUB LF
GOSUB TX
'-------------------LNG--------------------------------------------
ADDRESS = $F70 'LNG ADDRESS
FOR L = 0 TO 5
PEEKCODE ADDRESS, BAUDOTDATA
GOSUB TX
ADDRESS = ADDRESS + 1
NEXT L
FOR L = 0 TO 9 'MOVE LNG INTO RXDATA
RXDATA (L) = LNG (L)
GOSUB TRANSLATE 'TRANSLATE ASCII TO BAUDOT
GOSUB TX 'TRANSMIT BYTE
NEXT L
GOSUB CRTN
GOSUB TX
GOSUB LF
GOSUB TX
'----------------------------------------------------------------
ADDRESS = $F80 'ALT ADDRESS
FOR L = 0 TO 5
PEEKCODE ADDRESS, BAUDOTDATA
GOSUB TX
ADDRESS = ADDRESS + 1
NEXT L
FOR L = 0 TO 5 'MOVE ALT INTO RXDATA
RXDATA (L) = ALT (L)
GOSUB TRANSLATE 'TRANSLATE ASCII TO BAUDOT
GOSUB TX 'TRANSMIT BYTE
NEXT L
GOSUB CRTN
GOSUB TX
GOSUB LF
GOSUB TX
'-----------------------SPEED--------------------------
ADDRESS = $F90 'SPD ADDRESS
FOR L = 0 TO 5
PEEKCODE ADDRESS, BAUDOTDATA
GOSUB TX
ADDRESS = ADDRESS + 1
NEXT L
FOR L = 0 TO 3 'MOVE SPD INTO RXDATA
RXDATA (L) = SPD (L)
GOSUB TRANSLATE 'TRANSLATE ASCII TO BAUDOT
GOSUB TX 'TRANSMIT BYTE
NEXT L
GOSUB CRTN
GOSUB TX
GOSUB LF
GOSUB TX
'-----------------------TRACK---------------------------
ADDRESS = $FA0 'TRK ADDRESS
FOR L = 0 TO 5
PEEKCODE ADDRESS, BAUDOTDATA
GOSUB TX
ADDRESS = ADDRESS + 1
NEXT L
FOR L = 0 TO 4 'MOVE TRK INTO RXDATA
RXDATA (L) = TRK (L)
GOSUB TRANSLATE 'TRANSLATE ASCII TO BAUDOT
GOSUB TX 'TRANSMIT BYTE
NEXT L
GOSUB CRTN
GOSUB TX
GOSUB LF
GOSUB TX
RETURN
END
'---------------------TRANSLATE ACSII TO BAUDOT------------------
TRANSLATE:
IF RXDATA (L) = "0" THEN BAUDOTDATA = 13
IF RXDATA (L) = "1" THEN BAUDOTDATA = 29
IF RXDATA (L) = "2" THEN BAUDOTDATA = 25
IF RXDATA (L) = "3" THEN BAUDOTDATA = 16
IF RXDATA (L) = "4" THEN BAUDOTDATA = 10
IF RXDATA (L) = "5" THEN BAUDOTDATA = 1
IF RXDATA (L) = "6" THEN BAUDOTDATA = 21
IF RXDATA (L) = "7" THEN BAUDOTDATA = 28
IF RXDATA (L) = "8" THEN BAUDOTDATA = 12
IF RXDATA (L) = "9" THEN BAUDOTDATA = 3
IF RXDATA (L) = "," THEN BAUDOTDATA = 6 'Convert "," to SPACE
IF RXDATA (L) = "." THEN BAUDOTDATA = 7
RETURN
'------------------------------------------------------------------
TX:
GOSUB SPACE 'SEND START BIT LOW 22mS
BAUDOTBIT = BAUDOTDATA.BIT4
IF BAUDOTBIT = 0 THEN GOSUB SPACE
IF BAUDOTBIT = 1 THEN GOSUB MARK
BAUDOTBIT = BAUDOTDATA.BIT3
IF BAUDOTBIT = 0 THEN GOSUB SPACE
IF BAUDOTBIT = 1 THEN GOSUB MARK
BAUDOTBIT = BAUDOTDATA.BIT2
IF BAUDOTBIT = 0 THEN GOSUB SPACE
IF BAUDOTBIT = 1 THEN GOSUB MARK
BAUDOTBIT = BAUDOTDATA.BIT1
IF BAUDOTBIT = 0 THEN GOSUB SPACE
IF BAUDOTBIT = 1 THEN GOSUB MARK
BAUDOTBIT = BAUDOTDATA.BIT0
IF BAUDOTBIT = 0 THEN GOSUB SPACE
IF BAUDOTBIT = 1 THEN GOSUB MARK
GOSUB STOPBIT 'SEND STOP BIT HIGH 44mS
RETURN
'-----------------------METRIC TO SAE CONVERTION
METRICSAE:
IF ALT(4)=46 THEN GOSUB LOWER 'CHECK FOR "."
ALTFT = ((ALT(0)-48)*10000)+ ((ALT(1)-48)*1000)+ ((ALT(2)-48)*100)+ ((ALT(3)-48)*10)+(ALT(4)-48)
FEET = (ALTFT */ 845) 'CONVERT METERS TO FEET
GOSUB KNOTS
RETURN
LOWER:
ALTFT = ((ALT(0)-48)*1000)+ ((ALT(1)-48)*100)+ ((ALT(2)-48)*10)+ (ALT(3)-48)
FEET = (ALTFT */ 845)'CONVERT METERS TO FEET
KNOTS:
SPDMPH = ((SPD(0)-48)*10)+ (SPD(1)-48)
MPH = (SPDMPH */ 295) 'CONVERT KNOTS TO MPH
RETURN
'-----------------------CUTDOWN--------------------------
CUTDWN:
IF FEET > 61000 THEN HIGH PTT 'COUTDOWWN COMMAND SET FOR 61000'
PAUSE 5000 'SUPPLY CD CURRENT FOR 5 SECONDS
LOW CUT
RETURN
'-----------------------MARK AND SPACE-------------------
MARK:
low O
PAUSE 22
RETURN
SPACE:
high O
PAUSE 22
RETURN
STOPBIT:
low O
PAUSE 44
RETURN
'----------------------------------------------------------
LTR:
BAUDOTDATA = 31
RETURN
FIG:
BAUDOTDATA = 27
RETURN
CRTN:
BAUDOTDATA = 8
RETURN
LF:
BAUDOTDATA = 2
RETURN
'------------------------------------------------------------
BEACON:
ADDRESS = $F00 'BEACON TEXT STORAGE LOCATION
FOR L = 0 TO 51
PEEKCODE ADDRESS, BAUDOTDATA
GOSUB TX
ADDRESS = ADDRESS + 1
NEXT L
RETURN
'------------------------------------------------------
WEB:
ADDRESS = $F40 'BEACON TEXT STORAGE LOCATION
FOR L = 0 TO 28
PEEKCODE ADDRESS, BAUDOTDATA
GOSUB TX
ADDRESS = ADDRESS + 1
NEXT L
RETURN
END
'BEACONTEXT W6AB SARCHAB X1/HF TRACKING NET ON 7.180
POKECODE @$F00, 2,8,31,25,27,21,31,24,19,4,20,24,10,14,5,24
POKECODE @$F10, 19,4,23,27,29,27,2,8,31,5,22,4,1,10,24,14
POKECODE @$F20, 30,12,6,11,4,6,16,1,4,3,6,4,27,28,7,29
POKECODE @$F30, 12,13,2,8
'WEB ADDRESS F40 - F5C (29)
POKECODE @$F40, 31,25,25,25,27,7,31,20,24,1,16,9,9,12,1,16
POKECODE @$F50, 24,10,14,27,7,31,14,3,7,4,27,2,8
'LATITUDE: F60 - F6B (6)
POKECODE @$F60, 31,9,24,1,27,14
'LONGITUDE: F70 - F7C (6)
POKECODE @$F70, 31,9,3,6,27,14
'ALTITUDE: F80 - F8B (6)
POKECODE @$F80, 31,24,9,1,27,14
'SPEED:
POKECODE @$F90, 31,20,13,18,27,14
'TRACK:
POKECODE @$FA0, 31,1,10,30,27,14
'UTC:
POKECODE @$FB0, 31,28,1,14,27,14
Re: K42 and Timer Interrupts
Thanks for the explanation.
Ioannis - 28th April 2025, 19:28I misinterpreted these paragraphs. My understanding was to have ASYNC cleared and use Fosc/4.
Ioannis