Arduino Variable Duty-Cycle Square Wave Generator

basicsquare.ino

#define LED_pin 9

// Track LED state
bool LED_state = false;

// Set frequency of LED
float blinkrate = 1; // In Hz
float delay_between_switch = 500.0/blinkrate; // Blink at N Hz means you switch every 1s/(N/2)

// Track blinking cycle times of LED
long lastBlinkedTime;

void setup() {
  pinMode(LED_pin, OUTPUT);
  lastBlinkedTime = millis();
}

void loop() {
  long now = millis();
  if (now - lastBlinkedTime > delay_between_switch){
    digitalWrite(LED_pin, LED_state);
    LED_state = !LED_state;
    lastBlinkedTime = now;
  }
}

dutycycle.ino

#define LED_pin 9

// Track LED state
bool LED_state = false;

// Set frequency and duty cycle of LED
float blinkrate = 20; // In Hz
int dutyCycle = 80; // in percent (%)

// Since time slices are much smaller, use microseconds
float granularity = 100.0;
float delay_between_check = 1000000.0/blinkrate/granularity; // 1 sec/rate, divided into 100 segments
int cyclePosition = 0; // out of 100

// Track blinking cycle times of LED
long lastCheckedTime;

void setup() {
  pinMode(LED_pin, OUTPUT);
  lastCheckedTime = micros();

  Serial.begin(9600);
  Serial.println(delay_between_check);
}

void loop() {
  long now = micros();
  if (now - lastCheckedTime > delay_between_check){
    // Only turn LED on if current cycle position is less than the duty cycle
    if (cyclePosition < dutyCycle){
      digitalWrite(LED_pin, HIGH); 
    } else {
      digitalWrite(LED_pin, LOW); 
    }

    // Increment cycle position, zero it out if it's too big
    cyclePosition++;
    cyclePosition %= granularity;
    lastCheckedTime = now;
  }
}