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Function to generate square waves at desired frequencies

 
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kylemorin



Joined: 11 Mar 2007
Posts: 4

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Function to generate square waves at desired frequencies
PostPosted: Sun Mar 11, 2007 6:13 pm     Reply with quote

Hello all,

Here is an example program I made to demonstrate how to play sounds with a PIC microcontroller. It utilizes a function I wrote, "playtone()" to create a square wave of a set frequency (Hz) and set duration (ms).

Usage: playsound(float frequency, float duration);

Code:
//////////////////////////////////////////////////////////////////
////                           Playsound.C                    ////
////                                                          ////
////   Author: Kyle J. Morin                                  ////
////   Date: March 11, 2007                                   ////
////                                                          ////
////   Description: This example program shows how to         ////
////   manually generate sounds for a specified amount of     ////
////   time. The function playsound() was created as a        ////
////   a viable, more precise alternative to generate_tone()  ////
//////////////////////////////////////////////////////////////////

#INCLUDE <12F683.h>         // Include the standard header file for the PIC12F683                                   
#USE delay(clock=4000000)   // Tell the delay functions the processor speed (4 MHz) so delay timing is correct   
#FUSES nomclr, nowdt        // Master clear pin used for I/O, no watch dog timer                       


//***************************************************************//
// DESCRIPTION: Plays a specified sound for a specified duration //
// PARAMETERS: Frequency in hertz, duration in milliseconds      //
//***************************************************************//

int16   freq_truncated,   playtime_truncated;   // Declare 16-bit variables for frequency, playtime and delaytime     
int16   i;                                      // Declare i as a 16-bit counter variable (it will be used later in loops)   

void playsound(float frequency, float duration)
{
   frequency = 1000000 / frequency;    // This is to figure out how many microseconds each period will take to complete
   frequency = frequency - 72;         //  Offset this # by -72. This is because the instructions in the sound loop take
                                       //  time to complete and henceforth lower the actual frequency heard. We want precise tones.
   freq_truncated = frequency;         // Convert the 32-bit floating point frequency to a 16-bit number delay functions can understand
      duration = ( duration*1000 )/freq_truncated;  // Figure out how many cycles are required to play sound
   playtime_truncated = duration;      // This number is stored in the 16-bit "playtime_truncated" variable
   shift_right( &freq_truncated,2,0 ); // Divide freq_truncated by 2 using a "shift right" bit-shifting operation
                             
   for ( i=1 ;i <= playtime_truncated; ++i )  // This funciton creates the square wave audio output signal   
   {                                                                                 
      output_high( PIN_A2 );           // Turn PIN_A2 on                                   
      delay_us( freq_truncated );      // Delay for "freq_truncated" microseconds                 
      output_low( PIN_A2 );            // Turn PIN_A2 off                                   
      delay_us( freq_truncated );      // Delay for "freq_truncated" microseconds                 
   }
}

//**************************************************************//
// DESCRIPTION: Main loop                                       //
//**************************************************************//
void main()
{
   while(TRUE)                          // Loop forever                                                                     
   {                                                                                                   
      playsound( 500.0, 1000.0 );       // Create a 500 Hz square wave for 1 second
      delay_ms( 1000 );                 // Delay for 1 second
   }
}
longmenok



Joined: 23 Oct 2006
Posts: 11

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PostPosted: Wed Apr 18, 2007 4:57 am     Reply with quote

Thanks !!!
emelyjose



Joined: 13 Nov 2016
Posts: 5

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PostPosted: Wed Nov 16, 2016 10:10 am     Reply with quote

How do you implement the code to use it?
asmboy



Joined: 20 Nov 2007
Posts: 2116
Location: albany ny

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PostPosted: Tue Nov 22, 2016 5:18 pm     Reply with quote

1- what is the reason for using floats in the call to playsound() , when you immediately move them to 16 bit space.

do you know what happens when you ask for a frequency of 75000 hz ?

2-WHAT happens to playtime_truncated
if you attempt an assignment greater then 0xFFFF ??

3- do you know CCS has an unsigned int32 ??
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