James Wages <james <at> kiramek.com> writes:

>=20
> Joe & Sergey,
>=20
> Thank you for your replies.
>=20
> I downloaded the SIN wave generator code from the following link:
>=20
> http://www.g4jnt.com/PIC_DDS.zip
>=20

James,=20

I have developed a square wave generator with a scan function a while ago
(http://beaglerobotics.com/catalog.pl?pID=3D58).  The source code is in CCS=
 C,
but should be readable.  The relevant pieces of code are below.  Basically,
function set_f0() calculates settings for timer2 (PIC16F876A) and configure=
s
it.  When scanning the frequency, increment log(F) (variable log_f) at some
rate and call set_F0().  I believe I use log(F) to make scanning more smoot=
h. =20


#int_TIMER1
TIMER1_isr()
{
output_toggle(PIN_C1);
set_timer1(60536);
}

void set_f0()
{
	float ftemp;
	unsigned long ltemp;

	ftemp =3D ((float)log_f) /100;
	ltemp =3D (unsigned long) pow(10, ftemp);
	pr2_mult =3D 5000 / ltemp;

	if (pr2_mult < PR2_LOW_DIV1)  //set lower limit for pwm period
   {
      pr2_mult =3D PR2_LOW_DIV1;
   };
	if (pr2_mult <PR2_HIGH_DIV1)  //Prescale =3D 1
   {
		pr2 =3D make8 (pr2_mult, 0);
		setup_timer_2 (T2_DIV_BY_1, pr2, 1);
		set_pwm1_duty (pr2/2);
		return;
	};
	if (pr2_mult < PR2_HIGH_DIV4)  //prescale =3D 16
	{
   	pr2=3Dmake8 (pr2_mult / 4, 0);
		setup_timer_2 (T2_DIV_BY_4, pr2, 1);
		set_pwm1_duty (pr2/2);
		return;
	};
	if (pr2_mult > PR2_HIGH_DIV16)  //high limit for pwm period
   {
      pr2_mult =3D PR2_HIGH_DIV16;
   };
	pr2 =3D make8(pr2_mult / 16, 0);
	setup_timer_2 (T2_DIV_BY_16, pr2, 1);
	set_pwm1_duty (pr2/2);
	return;
}

///// in the main event loop:

if(scan) {
			delay_ms(scan_delay);
			switch (dir)
			{
			case 1: //Increase frequency
				log_f +=3D incr;
				if (log_f >=3D log_f_MAX)
				{
					dir =3D 2;
					log_f =3D log_f_MAX;
				};
				break;
			case 2: //Decrease frequency
				log_f -=3D incr;
				if (log_f <=3D log_f_MIN)
				{
					dir =3D1;
					log_f =3D log_f_MIN;
				};
				break;
			};

			set_f0();
			set_led_intensity();
		};


I can send the full source code if interested, please contact me off-list.
The code was written in 2007, and I have not used CCS C since about 2009,
the code might be a bit archaic. =20

Best,

Sergey=20



--=20
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