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direwolf/dtmf.c

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//
// This file is part of Dire Wolf, an amateur radio packet TNC.
//
// Copyright (C) 2013 John Langner, WB2OSZ
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 2 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//
/*------------------------------------------------------------------
*
* Module: dtmf.c
*
* Purpose: Decoder for DTMF, commonly known as "touch tones."
*
* Description: This uses the Goertzel Algorithm for tone detection.
*
* References: http://eetimes.com/design/embedded/4024443/The-Goertzel-Algorithm
* http://www.ti.com/ww/cn/uprogram/share/ppt/c5000/17dtmf_v13.ppt
*
*---------------------------------------------------------------*/
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <assert.h>
#include "direwolf.h"
#include "dtmf.h"
// Define for unit test.
//#define DTMF_TEST 1
#if DTMF_TEST
#define TIMEOUT_SEC 1 /* short for unit test below. */
#define DEBUG 1
#else
#define TIMEOUT_SEC 5 /* for normal operation. */
#endif
#define NUM_TONES 8
static int const dtmf_tones[NUM_TONES] = { 697, 770, 852, 941, 1209, 1336, 1477, 1633 };
/*
* Current state of the decoding.
*/
static struct {
int sample_rate; /* Samples per sec. Typ. 44100, 8000, etc. */
int block_size; /* Number of samples to process in one block. */
float coef[NUM_TONES];
struct { /* Separate for each audio channel. */
int n; /* Samples processed in this block. */
float Q1[NUM_TONES];
float Q2[NUM_TONES];
char prev_dec;
char debounced;
char prev_debounced;
int timeout;
} C[MAX_CHANS];
} D;
/*------------------------------------------------------------------
*
* Name: dtmf_init
*
* Purpose: Initialize the DTMF decoder.
* This should be called once at application start up time.
*
* Inputs: sample_rate - Audio sample frequency, typically
* 44100, 22050, 8000, etc.
*
* Returns: None.
*
*----------------------------------------------------------------*/
void dtmf_init (int sample_rate)
{
int j; /* Loop over all tones frequencies. */
int c; /* Loop over all audio channels. */
/*
* Processing block size.
* Larger = narrower bandwidth, slower response.
*/
D.sample_rate = sample_rate;
D.block_size = (205 * sample_rate) / 8000;
#if DEBUG
dw_printf (" freq k coef \n");
#endif
for (j=0; j<NUM_TONES; j++) {
float k;
// Why do some insist on rounding k to the nearest integer?
// That would move the filter center frequency away from ideal.
// What is to be gained?
// More consistent results for all the tones when k is not rounded off.
k = D.block_size * (float)(dtmf_tones[j]) / (float)(D.sample_rate);
D.coef[j] = 2 * cos(2 * M_PI * (float)k / (float)(D.block_size));
assert (D.coef[j] > 0 && D.coef[j] < 2.0);
#if DEBUG
dw_printf ("%8d %5.1f %8.5f \n", dtmf_tones[j], k, D.coef[j]);
#endif
}
for (c=0; c<MAX_CHANS; c++) {
D.C[c].n = 0;
for (j=0; j<NUM_TONES; j++) {
D.C[c].Q1[j] = 0;
D.C[c].Q2[j] = 0;
}
D.C[c].prev_dec = ' ';
D.C[c].debounced = ' ';
D.C[c].prev_debounced = ' ';
D.C[c].timeout = 0;
}
}
/*------------------------------------------------------------------
*
* Name: dtmf_sample
*
* Purpose: Process one audio sample from the sound input source.
*
* Inputs: c - Audio channel number.
* This can process multiple channels in parallel.
* input - Audio sample.
*
* Returns: 0123456789ABCD*# for a button push.
* . for nothing happening during sample interval.
* $ after several seconds of inactivity.
* space between sample intervals.
*
*
*----------------------------------------------------------------*/
__attribute__((hot))
char dtmf_sample (int c, float input)
{
int i;
float Q0;
float output[NUM_TONES];
char decoded;
char ret;
static const char rc2char[16] = { '1', '2', '3', 'A',
'4', '5', '6', 'B',
'7', '8', '9', 'C',
'*', '0', '#', 'D' };
for (i=0; i<NUM_TONES; i++) {
Q0 = input + D.C[c].Q1[i] * D.coef[i] - D.C[c].Q2[i];
D.C[c].Q2[i] = D.C[c].Q1[i];
D.C[c].Q1[i] = Q0;
}
/*
* Is it time to process the block?
*/
D.C[c].n++;
if (D.C[c].n == D.block_size) {
int row, col;
for (i=0; i<NUM_TONES; i++) {
output[i] = sqrt(D.C[c].Q1[i] * D.C[c].Q1[i] + D.C[c].Q2[i] * D.C[c].Q2[i] - D.C[c].Q1[i] * D.C[c].Q2[i] * D.coef[i]);
D.C[c].Q1[i] = 0;
D.C[c].Q2[i] = 0;
}
D.C[c].n = 0;
/*
* The input signal can vary over a couple orders of
* magnitude so we can't set some absolute threshold.
*
* See if one tone is stronger than the sum of the
* others in the same group multiplied by some factor.
*
* For perfect synthetic signals this needs to be in
* the range of about 1.33 (very senstive) to 2.15 (very fussy).
*
* Too low will cause false triggers on random noise.
* Too high will won't decode less than perfect signals.
*
* Use the mid point 1.74 as our initial guess.
* It might need some fine tuning for imperfect real world signals.
*/
#define THRESHOLD 1.74
if (output[0] > THRESHOLD * ( output[1] + output[2] + output[3])) row = 0;
else if (output[1] > THRESHOLD * (output[0] + output[2] + output[3])) row = 1;
else if (output[2] > THRESHOLD * (output[0] + output[1] + output[3])) row = 2;
else if (output[3] > THRESHOLD * (output[0] + output[1] + output[2] )) row = 3;
else row = -1;
if (output[4] > THRESHOLD * ( output[5] + output[6] + output[7])) col = 0;
else if (output[5] > THRESHOLD * (output[4] + output[6] + output[7])) col = 1;
else if (output[6] > THRESHOLD * (output[4] + output[5] + output[7])) col = 2;
else if (output[7] > THRESHOLD * (output[4] + output[5] + output[6] )) col = 3;
else col = -1;
for (i=0; i<NUM_TONES; i++) {
#if DEBUG
dw_printf ("%5.0f ", output[i]);
#endif
}
if (row >= 0 && col >= 0) {
decoded = rc2char[row*4+col];
}
else {
decoded = '.';
}
// Consider valid only if we get same twice in a row.
if (decoded == D.C[c].prev_dec) {
D.C[c].debounced = decoded;
/* Reset timeout timer. */
if (decoded != ' ') {
D.C[c].timeout = ((TIMEOUT_SEC) * D.sample_rate) / D.block_size;
}
}
D.C[c].prev_dec = decoded;
// Return only new button pushes.
// Also report timeout after period of inactivity.
ret = '.';
if (D.C[c].debounced != D.C[c].prev_debounced) {
if (D.C[c].debounced != ' ') {
ret = D.C[c].debounced;
}
}
if (ret == '.') {
if (D.C[c].timeout > 0) {
D.C[c].timeout--;
if (D.C[c].timeout == 0) {
ret = '$';
}
}
}
D.C[c].prev_debounced = D.C[c].debounced;
#if DEBUG
dw_printf (" dec=%c, deb=%c, ret=%c \n",
decoded, D.C[c].debounced, ret);
#endif
return (ret);
}
return (' ');
}
/*------------------------------------------------------------------
*
* Name: main
*
* Purpose: Unit test for functions above.
*
*----------------------------------------------------------------*/
#if DTMF_TEST
push_button (char button, int ms)
{
static float phasea = 0;
static float phaseb = 0;
float fa, fb;
int i;
float input;
char x;
static char result[100];
static int result_len = 0;
switch (button) {
case '1': fa = dtmf_tones[0]; fb = dtmf_tones[4]; break;
case '2': fa = dtmf_tones[0]; fb = dtmf_tones[5]; break;
case '3': fa = dtmf_tones[0]; fb = dtmf_tones[6]; break;
case 'A': fa = dtmf_tones[0]; fb = dtmf_tones[7]; break;
case '4': fa = dtmf_tones[1]; fb = dtmf_tones[4]; break;
case '5': fa = dtmf_tones[1]; fb = dtmf_tones[5]; break;
case '6': fa = dtmf_tones[1]; fb = dtmf_tones[6]; break;
case 'B': fa = dtmf_tones[1]; fb = dtmf_tones[7]; break;
case '7': fa = dtmf_tones[2]; fb = dtmf_tones[4]; break;
case '8': fa = dtmf_tones[2]; fb = dtmf_tones[5]; break;
case '9': fa = dtmf_tones[2]; fb = dtmf_tones[6]; break;
case 'C': fa = dtmf_tones[2]; fb = dtmf_tones[7]; break;
case '*': fa = dtmf_tones[3]; fb = dtmf_tones[4]; break;
case '0': fa = dtmf_tones[3]; fb = dtmf_tones[5]; break;
case '#': fa = dtmf_tones[3]; fb = dtmf_tones[6]; break;
case 'D': fa = dtmf_tones[3]; fb = dtmf_tones[7]; break;
case '?':
if (strcmp(result, "123A456B789C*0#D123$789$") == 0) {
dw_printf ("\nSuccess!\n");
}
else {
dw_printf ("\n *** TEST FAILED ***\n");
dw_printf ("\"%s\"\n", result);
}
break;
default: fa = 0; fb = 0;
}
for (i = 0; i < (ms*D.sample_rate)/1000; i++) {
input = sin(phasea) + sin(phaseb);
phasea += 2 * M_PI * fa / D.sample_rate;
phaseb += 2 * M_PI * fb / D.sample_rate;
/* Make sure it is insensitive to signal amplitude. */
x = dtmf_sample (0, input);
//x = dtmf_sample (0, input * 1000);
//x = dtmf_sample (0, input * 0.001);
if (x != ' ' && x != '.') {
result[result_len] = x;
result_len++;
result[result_len] = '\0';
}
}
}
main ()
{
dtmf_init(44100);
dw_printf ("\nFirst, check all button tone pairs. \n\n");
/* Max auto dialing rate is 10 per second. */
push_button ('1', 50); push_button (' ', 50);
push_button ('2', 50); push_button (' ', 50);
push_button ('3', 50); push_button (' ', 50);
push_button ('A', 50); push_button (' ', 50);
push_button ('4', 50); push_button (' ', 50);
push_button ('5', 50); push_button (' ', 50);
push_button ('6', 50); push_button (' ', 50);
push_button ('B', 50); push_button (' ', 50);
push_button ('7', 50); push_button (' ', 50);
push_button ('8', 50); push_button (' ', 50);
push_button ('9', 50); push_button (' ', 50);
push_button ('C', 50); push_button (' ', 50);
push_button ('*', 50); push_button (' ', 50);
push_button ('0', 50); push_button (' ', 50);
push_button ('#', 50); push_button (' ', 50);
push_button ('D', 50); push_button (' ', 50);
dw_printf ("\nShould reject very short pulses.\n\n");
push_button ('1', 20); push_button (' ', 50);
push_button ('1', 20); push_button (' ', 50);
push_button ('1', 20); push_button (' ', 50);
push_button ('1', 20); push_button (' ', 50);
push_button ('1', 20); push_button (' ', 50);
dw_printf ("\nTest timeout after inactivity.\n\n");
/* For this test we use 1 second. */
/* In practice, it will probably more like 10 or 20. */
push_button ('1', 250); push_button (' ', 500);
push_button ('2', 250); push_button (' ', 500);
push_button ('3', 250); push_button (' ', 1200);
push_button ('7', 250); push_button (' ', 500);
push_button ('8', 250); push_button (' ', 500);
push_button ('9', 250); push_button (' ', 1200);
/* Check for expected results. */
push_button ('?', 0);
} /* end main */
#endif
/* end dtmf.c */
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