Outputs Final Text COde

// XIAO RP2040 — LED on D7 driven linearly by A3 (dark=200, bright=4000)


const int SENSOR = A3;
const int LED_PIN = D7;


// ---- your calibration ----
const int RAW_DARK   = 200;   // reading at darkest
const int RAW_BRIGHT = 4000;  // reading at brightest


// ---- LED output (12-bit PWM) ----
const int PWM_RANGE = 4095;   // do not change
int   PWM_CAP   = 100;        // max brightness (0..4095) — raise if too dim
int   PWM_FLOOR = 0;          // small floor (e.g., 2–6) if you want a faint glow at "dark"
bool  LED_ACTIVE_HIGH = true; // set false if wired active-low


// smoothing (optional)
const float EMA_ALPHA = 0.15f; // 0..1 (higher = snappier)


float ema = 0;


static inline float clamp01(float x){ return x < 0 ? 0 : (x > 1 ? 1 : x); }


void setup() {
 Serial.begin(115200);
 analogReadResolution(12);


 // high-res PWM
 analogWriteResolution(12);
 analogWriteRange(PWM_RANGE);
 analogWriteFreq(1500);
 pinMode(LED_PIN, OUTPUT);


 // seed smoothing
 ema = analogRead(SENSOR);


 Serial.println("Linear A3 -> LED (dark=200, bright=4000)");
}


void loop() {
 int raw = analogRead(SENSOR);


 // smooth a bit so it doesn't jitter
 ema = (1.0f - EMA_ALPHA)*ema + EMA_ALPHA*raw;


 // linear normalize: RAW_DARK..RAW_BRIGHT -> 0..1
 float n = (ema - RAW_DARK) / float(RAW_BRIGHT - RAW_DARK);
 n = clamp01(n);


 // scale to (very) dim PWM range
 int pwm = int(n * PWM_CAP + 0.5f);
 if (pwm < PWM_FLOOR) pwm = PWM_FLOOR;
 if (pwm > PWM_CAP)   pwm = PWM_CAP;


 if (!LED_ACTIVE_HIGH) pwm = PWM_RANGE - pwm;


 analogWrite(LED_PIN, pwm);


 // debug (optional)
 static uint32_t t0=0;
 if (millis() - t0 > 250) {
   t0 = millis();
   Serial.print("A3 "); Serial.print(int(ema));
   Serial.print("  n "); Serial.print(n,3);
   Serial.print("  pwm "); Serial.println(pwm);
 }


 delay(8);
}