Fade needs to be smoother

[mattytrentini]

Fade needs to be smoother

[mattytrentini]

Tried a non-async 20ms step (1.5s 0-100%) fade and it's very smooth:

from machine import Pin, PWM
from time import sleep_ms
def fadein():
    led=PWM(Pin(12))
    for i in range(0, 1024, 13): # 13 = 1024/(1500ms/20ms)
        led.duty(i)
        sleep_ms(20)

[seanlano]

On the point:

Brightness appear to be non-linear

I found that using an exponential function gave a better-looking response - in my case in the WiLED project I had a notion of "brightness steps", i.e. the dimmer would change between say five distinct levels only, rather than the full range PWM values. Then I have a mapping between those brightness levels and an actual PWM value. I suppose if you wanted to do 100 "brightness steps" then those would effectively be a percentage to PWM mapping.

The C++ code I have for it is:

float max_log10 = log10(led->getMaxPWM());
float steps_log10 = log10(NUM_DIM_STEPS-1);
float exponent = max_log10/steps_log10;
float result;
pwm_dim_levels[0] = 0;
for(int idx=1; idx<NUM_DIM_STEPS; idx++){
	result = pow(idx,exponent);
	pwm_dim_levels[idx] = int(result);
}
pwm_dim_levels[NUM_DIM_STEPS-1] = led->getMaxPWM();

The gist of it is though, suppose you want 8-bit values and 6 steps, you find the exponent with exponent = log10(255)/log10(6) = 3.092638069 and then the actual value with pwm = step ^ exponent.

Then the values for each step are:

pwm_dim_levels[0] = 0
pwm_dim_levels[1] = 1
pwm_dim_levels[2] = 9
pwm_dim_levels[3] = 30
pwm_dim_levels[4] = 72
pwm_dim_levels[5] = 145
pwm_dim_levels[6] = 255

[mattytrentini]

Thanks @seanlano!

I was had intended to insert a mapping shim method - pass a function a value from 0-100 and then have it return a non linear value from 0-100. Something like what you've proposed ought to work well!

Looking forward to seeing your LED controller in the flesh... :)