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====== Осциллограф из звуковой платы ======

====== Схема ======

{{::soundcard_oscilloscope_probe-1.jpg?300|}}



====== Существующие программы ======

[[http://xoscope.sourceforge.net/ | xoscope]]

[[https://github.com/xobs/osqoop | Osqoop]] использует доступ к звуковой плате через драйвер OSS, поэтому на современных системах нуждается в [[http://alsa.opensrc.org/Aoss | его эмуляции]].






====== Своя программа ======

[[http://www.linuxjournal.com/article/6735?page=0,2 | 
Introduction to Sound Programming with ALSA]]

[[http://users.suse.com/~mana/alsa090_howto.html#sect03 | ALSA Programming HOWTO: PCM capture]]

[[http://equalarea.com/paul/alsa-audio.html | A Tutorial on Using the ALSA Audio API]]

[[http://www.alsa-project.org/main/index.php/Main_Page | Advanced Linux Sound Architecture (ALSA) project homepage]]

===== Пробная программа =====

<file c "soundcard_oscilloscope.c">
/*
  soundcard_oscilloscope.c

  v.0.1

  17.08.2013 Vladimir Smolyar

  GPLv3

*/



#include <stdio.h>
#include <stdlib.h>
#include <alsa/asoundlib.h>
#include <math.h>
	      
main (int argc, char *argv[])
{
    int i,j;
    int err;
    int buf[128];
    snd_pcm_t *capture_handle;
    snd_pcm_hw_params_t *hw_params;
    unsigned int val,val2;
    int dir;
    int peak_value, average;
    size_t size;
    int number;

    err = snd_pcm_open (&capture_handle, argv[1], SND_PCM_STREAM_CAPTURE, 0);
    if (err < 0) 
    {
        fprintf (stderr, "cannot open audio device %s (%s)\n", 
                 argv[1],
                 snd_strerror (err));
        exit (1);
    }
    else printf("Audio device opened.\n");

    err = snd_pcm_hw_params_malloc (&hw_params);
    if (err < 0) 
    {
        fprintf(stderr, "cannot allocate hardware parameter structure (%s)\n",
	         snd_strerror(err));
	exit (1);
    }
    else printf("Hardware parameter structure allocated.\n");

    err = snd_pcm_hw_params_any(capture_handle, hw_params);
    if (err < 0) 
    {
        fprintf(stderr, "cannot initialize hardware parameter structure (%s)\n",
		 snd_strerror (err));
	exit (1);
    }
    else printf("Hardware parameter structure initialized.\n");
    

    err = snd_pcm_hw_params_set_access (capture_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED);
    if (err < 0) 
    {
        fprintf (stderr, "cannot set access type (%s)\n",
		 snd_strerror (err));
	exit (1);
    }
    else printf("Access type set.\n");


    err = snd_pcm_hw_params_set_format (capture_handle, hw_params, SND_PCM_FORMAT_S16_LE);
    if (err < 0) 
    {
        fprintf (stderr, "cannot set sample format (%s)\n",
		 snd_strerror (err));
	exit (1);
    }
    else printf("Sample format set.\n");

    val = 44100;
    err = snd_pcm_hw_params_set_rate_near (capture_handle, hw_params, &val, &dir);
    if (err < 0) 
    {
        fprintf (stderr, "cannot set sample rate (%s)\n",
		 snd_strerror (err));
	exit (1);
    }
    else printf("Sample rate set.\n");

    err = snd_pcm_hw_params_set_channels (capture_handle, hw_params, 1);
    if (err < 0) 
    {
        fprintf (stderr, "cannot set channel count (%s)\n",
		 snd_strerror (err));
	exit (1);
    }
    else printf("Channel count set.\n");
    

    err = snd_pcm_hw_params (capture_handle, hw_params);
    if (err < 0) 
    {
        fprintf(stderr, "cannot set parameters (%s)\n",
	        snd_strerror (err));
        exit (1);
    }
    else printf("Parameters set.\n");
	
    snd_pcm_hw_params_free (hw_params);
    err = snd_pcm_prepare (capture_handle);
    if (err < 0) 
    {
        fprintf (stderr, "cannot prepare audio interface for use (%s)\n",
		 snd_strerror (err));
        exit (1);
    }
    else printf("Audio interface prepared for use.\n");
	
    //for (i = 0; i < 10; ++i) 
    peak_value = 0;
    average = 0;
    while (1)
    {
        err = snd_pcm_readi (capture_handle, buf, 128);
	if (err != 128)
	{
            fprintf (stderr, "read from audio interface failed (%s)\n",
	             snd_strerror (err));
            exit (1);
        }
	
	else 
	{    
	    //printf("%d\n",abs(buf[0]));
	    //printf("%d\n",abs(peak_value));
	    //printf(".\n");

	    for (i=0; i<128; i++)
	    {
	        average += (abs(buf[i]) - average)/512;
		if (abs(buf[i]) > abs(peak_value))
		{
		    peak_value = buf[i];
	            //printf("Peak: %d\n",peak_value);
		    //write(1, *peak_value, sizeof(peak_value));

		}
	    }
	    printf("|");
	    number = round(100 * ((float) average) / 2147483648);
	    for (j=0; j < number; j++) printf("=");
	    printf(">");
	    for (j=number; j < 70; j++) printf("-");
	    //printf("average: %d\n",average);
	    printf("|\n");
        } 
    }
    snd_pcm_close (capture_handle);
    exit (0);
}
</file>


====== Статьи ======

[[http://www.energeticforum.com/renewable-energy/3901-el-cheapo-oscilloscope-using-pc-soundcard.html | El-Cheapo Oscilloscope using PC + soundcard]]

[[http://www.instructables.com/id/Use-Your-Laptop-as-Oscilloscope/?ALLSTEPS | Use Your Laptop as Oscilloscope]]

[[http://www.opencircuits.com/Oscilloscope]]