Setting custom pwm sequence

Projects General Guidance
1

Hi, I am trying to create a custom PWM sequence for Arduino Uno pin 6 PWM output:

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image1679×446 11.6 KB

The PWM frequency is 62.5kHz and duty cycle should be 50%. I am using the following code, but cannot get the starting at 300us pin high followed by 3 pulses at 62.5kHz followed by the pin being high forever.

Currently, I get 3 pulses at 62.5kHz at the beginning (rather than a 300us or in the case I have implemented in code, a 100ms high output followed by the pulse) and after delay the pulse continues forever

This is the code I am running:

int outputPin = 6;

void setup(){
  pinMode(outputPin, OUTPUT);
  setPwmFrequency(6, 1);
  // delay(1000);
  analogWrite(outputPin, 255);
  delay(100);
  
  // analogWrite(outputPin, 0);
  // delayMicroseconds(10);
  // digitalWrite(outputPin, HIGH);
}

void loop(){
  for(int i=0; i<3; i++){
    analogWrite(outputPin, 127);
    // delay(100);
  }
  exit(0);
}

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;
  }
}

What could be going wrong that I cannot see my expected behavior?

2

What comes out of that code?
Not being 200% expert this sounds strange. From what is that 300 uS counted? Why involve PWM? It makes no sense just sending a few pulses.

Please give us the big picture showing why this? No helper like spending time finding a solution to Your question just to hear the next day: "It doesn't work".

3

If this sequence can be blocking, you may want to consider using

 __builtin_avr_delay_cycles ( );

https://forum.arduino.cc/t/causing-a-delay-while-in-an-interrupt/358488/3

4

You're not really trying to generate a pwm signal so much as you are trying to generate 3 pulses. A pwm signal is continuous. It doesn't stop after only 3 pules. Why not simply do this:

digitalWrite(PIN, LOW);
delayMicroseconds(300);
digitalWrite(PIN, HIGH);
delayMicroseconds(300);
digitalWrite(PIN, LOW);

etc, etc. That would be a lot simpler than trying to generate a PWM signal for 3 pulses.

5

beat me to it, although I was suggesting using micros() for timing.

while the OP COULD use a for() loop its hardly worth it for three pulses - unless thats just an example.

6

I'm not a big fan of blocking code either, since it usually causes problems with most systems, especially anything with wifi. But 300us is so fast, that blocking isn't blocking for long.

7

Currently my code does the following:

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image1804×336 11.6 KB

so no dc bias for 300us and and infinite sequence of 62.5khz pulse after 3 pulses. The 3 pulse is an example, I will need a maximum pulse count of 40 pulses for my application used to adjust voltage on a inverting boost.

8

Does this create one 62.5kHz pulse?

9

No just get a 80ms pulse:

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image1743×959 136 KB

10

Did you replace each instance of PIN with outputPin to write to pin 6?

11

Yes actually I tried putting in setup() but in loop() works fine

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But goes on forever

12 
int pulse= HIGH;
if (pulse) {
digitalWrite(PIN, HIGH);
delayMicroseconds(300);
digitalWrite(PIN, LOW);
delayMicroseconds(8);
digitalWrite(PIN, HIGH);
delayMicroseconds(8);
digitalWrite(PIN, LOW);
delayMicroseconds(8);
digitalWrite(PIN, HIGH);
pulse=LOW;
}

Add your pulses to this profile

13

If you are trying to generate a set of 3 pulses at different times, it would be easier to put that into it's own function and call it from whereever you are triggering it from.

14

SPI ...

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image740×147 4.43 KB

15

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