I guess this is the correct place to put this...
FFT code from: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1286718155
This program decoders 45.4 RTTY on analog 0 and outputs it to the serial console.
It has quite a bit of limitations.
RTTY shift has to be between 160-182hz.
It has to be ~45.4 baud.
The decode output has errors in it and its just a proof of concept but still cool.
--edit--
Also the RTTY center frequency has to be 300hz +/- 10
#include <avr/pgmspace.h>
#include "fixfft.h"
#include "fix_fft.cpp"
#define THRESH 27 //Bit threshold adjust for best decode
#define CHK(x) (sqrt(real[x] * real[x] + imag[x] * imag[x])) Convert FFT output to more usable form
#define PCK(ar) (ar[0] | ar[1]<<1 | ar[2] << 2 | ar[3] << 3 | ar[4] << 4) //Pack bits into byte
unsigned char lookup[] = { //Baudot lookup table
' ', 'E' , ' ', 'A', ' ', 'S', 'I', 'U',
'\n', 'D', 'R', 'J', 'N', 'F', 'C', 'K',
'T', 'Z', 'L', 'W', 'H', 'Y', 'P', 'Q',
'O', 'B', 'G', 0, 'M', 'X', 'V', 0, ' ',
'3', '\n', '-', ' ', '`', '8', '7',
'\r', ' ', '4', ' ', ',', '!', ':', '(',
'5', '+', ')', '2', '
, '6', '0', '1',
'9', '?', '&', 0, '.', '/', ';', 0};
int toffset=0; //Symbols and numbers shift
void setup(){
Serial.begin(115200); //115200 baud output
digitalWrite(A0, 1); //Turn this off depending on input source
}
void loop(){
char bits[6]={0,0,0,0,0};
char real[32],imag[32];
int ticker = 0;
unsigned char pbyte;
for(int a = 0;a < 16;a++){
real[a] = (analogRead(A0)-512) / 4; //Get samples
imag[a] = 0;
delayMicroseconds(780);
}
fix_fft(real, imag, 4, 0); //Preform FFT
if(CHK(6) > THRESH){ //Got a start bit?
for(int b = 0;b < 5;b++){ //Yes - start collecting bits
delay(7); //For timing
for(int a = 0;a < 16;a++){
real[a] = (analogRead(A0)-512) / 4; //Get more samples
imag[a] = 0;
delayMicroseconds(780);
}
fix_fft(real, imag, 4, 0); //Preform FFT
bits[b] = (CHK(6) > THRESH)? 0:1; //Check if we got a 1 or a 0
// bits[b] = (CHK(7) > THRESH)? 1:0;
}
pbyte = PCK(bits); //Pack the byte
if(pbyte == 0x1B){toffset=0x20; pbyte=0;} //Handle character set shift
if(pbyte == 0x1F){toffset=0x00; pbyte=0;}
Serial.print(lookup[pbyte+toffset]); //Print output
ticker++;
//if(ticker>60){ticker=0; Serial.println();}
/* for(int b = 0;b< 5;b++){
}*/
// Serial.println();
delay(12); //For timing
}
}
