Problem with getting sine wave with variable frequency (FastLED library)

Projects Programming
1

Hi!

I'm trying to get a sin wave using beat8 function in FastLED library to make led strip fade.
beat8 allows to set the BMP minimum and maximum value (from 0 to 255).
The value I want to change is the BMP (beats per minute). However, as I change it, the wave glitches (as on the immage). It doesn't start at "0" but somewhere in the middle as the BMP value is updated.

My function looks like this

void draw_white_breathing_leds(){
Serial.print(breath_bright); Serial.print(",");     //for debug
Serial.print(BMP); Serial.print(",");
Serial.println(speed_val);
    
FastLED.clear();
breath_bright = beatsin8(BMP, 0, bright_val);
   
   if(breath_bright <= 0){    //Update BMP value when leds are off
      BMP = speed_val;
    }
   else{}

  for (int led = 0; led < num_leds_val; led++) {          
        leds[led] = CRGB(breath_bright,breath_bright,breath_bright);
      }

  FastLED.show();
  }

I'm using rotary encoders to get those values so I'd like to keep the code as fast as possible. I tried many techniques to get a smooth fading wave. So far this one is my best attempt but still not enough.

How can I get a smooth sinusoidal/triangular wave with variable BMP?

plotter.png
plotter.png1270×648 69.9 KB

2

looks like the discontinuity is near when the sine value is ~0

why do you change BMP when breath_bright is <= 0?

3

Just trying to get the smoothest wave. Still not perfect because it means that I have to wait the whole cycle to change the BMP. But the glitch looks better with it.

This is how it looks when I update the BMP on "live".