RC filters - various use

[ivconic]

[ivconic]

My main goal was not to play with this filter but to pick the better behavior between TDA7231 and LM386, when supplied with only 5v.
I used the code that generates signal even above 6kHz (400Hz to 15kHz adjustable with pot), also to be able to check the filter response as well.

#include "avr/pgmspace.h"
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x3F, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);


PROGMEM const int sine256[] = {
127,130,133,136,139,143,146,149,152,155,158,161,164,167,170,173,176,178,181,184,187,190,192,195,198,200,203,205,208,210,212,215,217,219,221,223,225,227,229,231,233,234,236,238,239,240,
242,243,244,245,247,248,249,249,250,251,252,252,253,253,253,254,254,254,254,254,254,254,253,253,253,252,252,251,250,249,249,248,247,245,244,243,242,240,239,238,236,234,233,231,229,227,225,223,
221,219,217,215,212,210,208,205,203,200,198,195,192,190,187,184,181,178,176,173,170,167,164,161,158,155,152,149,146,143,139,136,133,130,127,124,121,118,115,111,108,105,102,99,96,93,90,87,84,81,78,
76,73,70,67,64,62,59,56,54,51,49,46,44,42,39,37,35,33,31,29,27,25,23,21,20,18,16,15,14,12,11,10,9,7,6,5,5,4,3,2,2,1,1,1,0,0,0,0,0,0,0,1,1,1,2,2,3,4,5,5,6,7,9,10,11,12,14,15,16,18,20,21,23,25,27,29,31,
33,35,37,39,42,44,46,49,51,54,56,59,62,64,67,70,73,76,78,81,84,87,90,93,96,99,102,105,108,111,115,118,121,124 };
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#define OutputPin 11
int dfreq = 3000;
const double refclk=31376.6; 
volatile byte icnt; 
volatile byte icnt1; 
volatile byte c4ms; 
volatile unsigned long phaccu; 
volatile unsigned long tword_m; 
const int buttonPin = 4;  
int buttonState = 0;
int flag=0;
int potPin = A3;
int val = 0; 
 
void setup()
{
  pinMode(buttonPin, INPUT_PULLUP); 
  
pinMode(OutputPin, OUTPUT); 
Setup_timer2();
cbi (TIMSK0,TOIE0); 
sbi (TIMSK2,TOIE2); 
tword_m=pow(2,32)*dfreq/refclk; 
lcd.begin(16,2);
lcd.clear (); 
TWORD();
Ispis();
}
void loop()
{
 buttonState = digitalRead(buttonPin);
 if (buttonState == HIGH) 
 {
  podesavanje();
 }
}
void Setup_timer2() 
{
sbi (TCCR2B, CS20);
cbi (TCCR2B, CS21);
cbi (TCCR2B, CS22);
cbi (TCCR2A, COM2A0); 
sbi (TCCR2A, COM2A1);
sbi (TCCR2A, WGM20); 
cbi (TCCR2A, WGM21);
cbi (TCCR2B, WGM22);
}
ISR(TIMER2_OVF_vect) {
sbi(PORTD,7); 
phaccu=phaccu+tword_m; 
icnt=phaccu >> 24; 
OCR2A=pgm_read_byte_near(sine256 + icnt);
if(icnt1++ == 125) { 
c4ms++;
icnt1=0;
}
cbi(PORTD,7); 
}
void TWORD()
{
  tword_m=pow(2,32)*dfreq/refclk; 
}
void podesavanje()
{
  val = analogRead(potPin); 
  dfreq = map(val,0,1023,400,15000);
  lcd.setCursor(8, 0);
  lcd.print(val);
  lcd.print("  ");
  lcd.setCursor(8, 1);
  lcd.print(dfreq);
  lcd.print("  ");
  TWORD();
}
void Ispis()
{
  lcd.setCursor(0, 0);
  lcd.print("Value");
  lcd.setCursor(8, 0);
  lcd.print(val);
  lcd.print("  ");
  lcd.setCursor(0, 1);
  lcd.print("dfreq");
  lcd.setCursor(8, 1);
  lcd.print(dfreq);
  lcd.print("  ");
}