Converting an Arduino PWM Output to a DAC Output

In this video we look at how to convert a PWM output or signal to a analog or DAC signal.

To access the low pass filter tutorial mentioned in the video got to: https://youtu.be/gW5oF8vcYb8


//*************Arduino code from video***************************
/*This code was made for a vidoe tutorial on the ForceTronics YouTube Channel called
 * Converting an Arduino PWM Output to a DAC Output. This code is free to use and 
 * modify at your own risk
 */

uint8_t pVal = 127; //PWM value 
const float pi2 = 6.28; //Pie times 2, for building sinewave
const int samples = 100; //number of samples for Sinewave. This value also affects frequency
int WavSamples[samples]; //Array for storing sine wave points
int count = 0; //tracks where we are in sine wave array

void setup() {
// Serial.begin(115200); //for debugging
  pinMode(10, OUTPUT); //pin used for analog voltage value
  pinMode(4,OUTPUT); //pin used to fake PWM for sinewave
  setPwmFrequency(10,1); //function for setting PWM frequency
  analogWrite(10,127); //set duty cycle for PWM

  float in, out; //used for building sine wave
  
  for (int i=0;i<samples;i++) //loop to build sinewave
  {
    in = pi2*(1/(float)samples)*(float)i; //calculate value for sine function
    WavSamples[i] = (int)(sin(in)*127.5 + 127.5); //get sinewave value and store in array
   // Serial.println(WavSamples[i]); //for debugging
  }
}

void loop() {
  if(count > samples) count = 0; //reset the count once we are through array
  bitBangPWM(WavSamples[count],4); //function for turning sinewave into "fake" PWM signal
  count++; //increment position in array
}

//Function to bit bang a PWM signal (we are using it for the sinewave)
//input are PWM high value for one cycle and digital pin for Arduino
//period variable determines frequency along with number of signal samples
//For this example a period of 1000 (which is 1 millisecond) times 100 samples is 100 milli second period so 10Hz
void bitBangPWM(unsigned long on, int pin) {
  int period = 1000; //period in micro seconds
  on = map(on, 0, 255, 0, period); //map function that converts from 8 bits to range of period in micro sec
 // Serial.println(on); //debug check
  unsigned long start = micros(); //get current value of micro second timer as start time
  digitalWrite(pin,HIGH); //set digital pin to high
  while((start+on) > micros()); //wait for a time based on PWM duty cycle
  start = micros(); 
  digitalWrite(pin,LOW); //set digital pin to low
  while((start+(period - on)) > micros()); //wait for a time based on PWM duty cycle
}

/**
 * https://www.arduino.cc/en/Tutorial/SecretsOfArduinoPWM
 * Divides a given PWM pin frequency by a divisor.
 * 
 * The resulting frequency is equal to the base frequency divided by
 * the given divisor:
 *   - Base frequencies:
 *      o The base frequency for pins 3, 9, 10, and 11 is 31250 Hz.
 *      o The base frequency for pins 5 and 6 is 62500 Hz.
 *   - Divisors:
 *      o The divisors available on pins 5, 6, 9 and 10 are: 1, 8, 64,
 *        256, and 1024.
 *      o The divisors available on pins 3 and 11 are: 1, 8, 32, 64,
 *        128, 256, and 1024.
 * 
 * PWM frequencies are tied together in pairs of pins. If one in a
 * pair is changed, the other is also changed to match:
 *   - Pins 5 and 6 are paired on timer0
 *   - Pins 9 and 10 are paired on timer1
 *   - Pins 3 and 11 are paired on timer2
 * 
 * Note that this function will have side effects on anything else
 * that uses timers:
 *   - Changes on pins 3, 5, 6, or 11 may cause the delay() and
 *     millis() functions to stop working. Other timing-related
 *     functions may also be affected.
 *   - Changes on pins 9 or 10 will cause the Servo library to function
 *     incorrectly.
 * 
 * Thanks to macegr of the Arduino forums for his documentation of the
 * PWM frequency divisors. His post can be viewed at:
 *   http://forum.arduino.cc/index.php?topic=16612#msg121031
 */
void setPwmFrequency(int pin, int divisor) {
  byte mode;
  if(pin == 5 || pin == 6 || pin == 9 || pin == 10) {
    switch(divisor) {
      case 1: mode = 0x01; break;
      case 8: mode = 0x02; break;
      case 64: mode = 0x03; break;
      case 256: mode = 0x04; break;
      case 1024: mode = 0x05; break;
      default: return;
    }
    if(pin == 5 || pin == 6) {
      TCCR0B = TCCR0B & 0b11111000 | mode;
    } else {
      TCCR1B = TCCR1B & 0b11111000 | mode;
    }
  } else if(pin == 3 || pin == 11) {
    switch(divisor) {
      case 1: mode = 0x01; break;
      case 8: mode = 0x02; break;
      case 32: mode = 0x03; break;
      case 64: mode = 0x04; break;
      case 128: mode = 0x05; break;
      case 256: mode = 0x06; break;
      case 1024: mode = 0x07; break;
      default: return;
    }
    TCCR2B = TCCR2B & 0b11111000 | mode;
  }
}