LEDs operating one at a time, not simultaneously

Other Hardware LEDs and Multiplexing
1

This code controls the brightness of each LED connected to pins 2, 3, 4, and 5 simultaneously. The starting brigthness for each LED is different, as you can see in the PWM[4] array. I confirmed that the PWM values are changing simultaneously in the serial monitor, but in the actual operation, I observed that the LEDs operate only one at a time, not simultaneously. What could be the problem? I apologize if my English is not perfect as I used a translator. Thank you.

int pins_LED[] = {2, 3, 4, 5};
int PWM[4] = {0, 63, 127, 191};

void setup() 
{
  Serial.begin(9600);
  for (int i = 0; i < 4; i++)
    pinMode(pins_LED[i], OUTPUT);
}

void loop()
{
  for (int i = 0; i < 4; i++)
  {
    analogWrite(pins_LED[i], PWM[i]);
    if (PWM[i] > 255) PWM[i] = 0;
    else PWM[i] = PWM[i] + 1;
    
    Serial.print(String(PWM[i]) + " ");
  }
  Serial.println();
}
2

Which board are you using? Note that on e.g. an Uno pins 2 and 4 are not PWM capable pins.

What happens if you remove the serial prints?

3

I am using Arduino Mega2560 board, so all 2~5 pin have PWM function.
If I remove Serial prints, the LED brightness changes faster but still happens one at a time.

Here's the video link: https://photos.app.goo.gl/3aYD2pToxL6NRc1SA

4

Is that with or without the prints? Note that printing takes time once the software buffer fills up.

5

I think I solved the problem. Deleting the printing and setting the delay shorter made it look clearer. Thank you!

6

Which delay? There was no delay in your original code in the opening post.

7

I deleted the printings and found out the changing speed was too fast, so I added delay(7) at the end of the loop.

8

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