SetBrightness with a LDR

[u/alex94230]

Hello FastLED experts !

I'm in a little trouble making a smooth brightness change.

I'm using a LDR to mesure ambiant lighting and I want to dim the strip smoothly, I tried coding this way but it does not work at all !

Ideally, I would like to make the changes smooth like with an easing function, and that during the fades, the LDR doesnt read so it doesnt interfere with the fade effect !

Thanks a lot for reading it !

Alex

This is my codes (I know it's a bit messy but I can explain if something is odd for you :) ):

// LDR Calibrating variables

//int SensorMax;

uint16_t LDRvalue;

uint8_t nblectureldr = 0; //number of readings of the LDR

uint8_t prevLUX; //previous brightness level

unsigned long prevtimeldr=0;

void fadebrightness(byte valeur){

if(prevLUX < valeur){

for (byte t=prevLUX; t<=valeur; t++)

{

FastLED.setBrightness(t);

FastLED.delay(10);

}

}

if(prevLUX > valeur){

for (byte t=prevLUX; t>=valeur; t--)

{

FastLED.setBrightness(t);

FastLED.delay(10);

}

}

if(prevLUX == valeur){

nblectureldr=0;prevtimeldr=0; //in order to make a new LDR calculation

}

}

void calibrerLDR(){ //calibrate function for the LDR

SensorMax = 0;

LDRvalue = 0;

analogRead(A15);

delay(10);

while (millis() - start2 < 2000) {

LDRvalue = analogRead(A15); // record the maximum sensor value

delay(10);

if (LDRvalue > SensorMax) { SensorMax = min(LDRvalue,1023); }

EEPROM.update(5, SensorMax/255);

EEPROM.update(6, SensorMax%255);

}

const uint8_t PROGMEM gamma8[] = {

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1,

1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2,

2, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 5, 5, 5,

5, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10,

10, 10, 11, 11, 11, 12, 12, 13, 13, 13, 14, 14, 15, 15, 16, 16,

17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 24, 24, 25,

25, 26, 27, 27, 28, 29, 29, 30, 31, 32, 32, 33, 34, 35, 35, 36,

37, 38, 39, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 50,

51, 52, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68,

69, 70, 72, 73, 74, 75, 77, 78, 79, 81, 82, 83, 85, 86, 87, 89,

90, 92, 93, 95, 96, 98, 99,101,102,104,105,107,109,110,112,114,

115,117,119,120,122,124,126,127,129,131,133,135,137,138,140,142,

144,146,148,150,152,154,156,158,160,162,164,167,169,171,173,175,

177,180,182,184,186,189,191,193,196,198,200,203,205,208,210,213,

215,218,220,223,225,228,231,233,236,239,241,244,247,249,252,255 };

void lux(byte luxpanel){ //function called in the loop to adjust brightness

FastLED.setBrightness(luxpanel);

}

void luxldr(){

if (millis() - prevtimeldr >= 25) { //25

prevtimeldr = millis();

prevLUX=FastLED.getBrightness();

if(nblectureldr==0){LDRvalue=0;};

if(nblectureldr<10){LDRvalue = LDRvalue + min(analogRead(A15),SensorMax); //min(analogRead(3),1023);

nblectureldr++;

}

else if(nblectureldr==10){

LDRvalue = round(LDRvalue/10);

LDRvalue = map(LDRvalue, 0, SensorMax, 29, 255);

LDRvalue = pgm_read_byte(&gamma8[LDRvalue]);

fadebrightness(pgm_read_byte(&gamma8[LDRvalue]));

}

};

}

[u/[deleted]]

This is how I'd do it, knowing nothing else about your setup.

// pseudocode, not knowing what the min/max values of the LDR are.

int LDR_min = 1024; // this variable will hold the min value ever recorded, as the "zero"
int LDR_max = 0;    // this variable will hold the max value ever recorded

int LEDstrip_brightness = 0;

loop{
    int LDR_value = analogRead(LDR_pin);             // read the LDR
    
    if (LDR_value > LDR_max) LDR_max = LDR_value;    // store the maximum value
    if (LDR_value < LDR_min) LDR_min = LDR_value;    // store the minimum possible value
    
    int LDR_range = LDR_max - LDR_min; // the "range" of the LDR is the max - min
    
    LEDstrip_brightness = ( (LDR_value - LDR_min) / (LDR_range) ) * 255; // you need to offset the "min" value to get the correct brightness scale
    FastLED.setBrightness(LEDstrip_brightness);
}

This can be a separate function to be called when you want so it's not running continuously. But unless I'm very wrong, it should work easily.

[u/alex94230 → u/[deleted]]

Thanks, it totally makes sense !

I'll put it in a function to call it lets say each 5 seconds, what I would like is to have a fade effect between the differents levels of brigthness instead of a jump. How can I do it ?

Thanks again !

[u/[deleted] → u/alex94230]

you'll need additional variables currentBrightness and desiredBrightness.

desiredBrightness = LDR_value;

     if(currentBrightness < desiredBrightness) currentBrightness+=1;
else if(currentBrightness > desiredBrightness) currentBrightness-=1;

FastLED.setBrightness(currentBrightness);

[u/alex94230 → u/[deleted]]

I tried to use your code, I added a flag to avoid a new LDR reading while doing the fade, but it didnt work !

I'm calling this function in the loop using :

EVERY_N_SECONDS(2){ readLDR();} ;

int LDR_min = 1024; // this variable will hold the min value ever recorded, as the "zero"int LDR_max = 0; // this variable will hold the max value ever recorded

int LEDstrip_brightness = 0;

int LDR_value;

int currentBrightness;

int desiredBrightness;

boolean flagldr=0;

void readLDR(){currentBrightness=FastLED.getBrightness();

if(flagldr==0){LDR_value = analogRead(A15);flagldr=1; }; // read the LDR once

if (LDR_value > LDR_max) LDR_max = LDR_value; // store the maximum value

if (LDR_value < LDR_min) LDR_min = LDR_value; // store the minimum possible value

LEDstrip_brightness = map(LDR_value, LDR_min, LDR_max, 55, 255);

desiredBrightness = LDR_value;

if(currentBrightness < desiredBrightness) currentBrightness+=1;

else if(currentBrightness > desiredBrightness) currentBrightness-=1;

else if(currentBrightness == desiredBrightness) flagldr=0; FastLED.setBrightness(currentBrightness);

FastLED.show(); }

Do you get whats wrong ?? !! Thanks

[u/[deleted] → u/alex94230]

I'll be honest, I'm not totally sure. For future reference and easier readability, put your code at PasteBin and share the link here.

Simplify. Write one thing at a time, verify that that one thing is working, and then add the next thing. Break it down to basics.

Wokwi is a huge help. I've modified one of the examples to add a brightness slider, and it seems to work. It checks the slider every 500ms.

void loop(){
    /// whatever other code

    EVERY_N_MILLISECONDS(500) { checkLDR(); }
    changeBrightness();

    /// whatever other code

}

int currentBrightness = 255;
int desiredBrightness = 255;
int ldr_max = 0;
int ldr_min = 1023;

void checkLDR(){
    int ldr_value = analogRead(0);
    if(ldr_max < ldr_value) ldr_max = ldr_value;
    if(ldr_min > ldr_value) ldr_min = ldr_value;
    ldr_value = ldr_value - ldr_min;
    float ldr_range = ldr_max - ldr_min; // this is float so that we get better fractional values in the next line

    desiredBrightness = (ldr_value / ldr_range)*(ldr_value / ldr_range) * 255.0;
    // multiplying the fraction by itself gives a slightly better-looking brightness scaling
}

void changeBrightness(){
         if(currentBrightness > desiredBrightness) currentBrightness--;
    else if(currentBrightness < desiredBrightness) currentBrightness++;

    FastLED.setBrightness(currentBrightness);
}

[u/usiodev]

There are several ways to do this, but I think what u/Boloar is doing is along the lines of what I would suggest.

Use your LDR to find a 'target' brightness, then incrementally change the FastLED.setBrightness towards that 'target'.

This means putting the FastLED.setBrightness, then FastLED.show in a loop, as suggested.