Motion night light (PIR on 12, RGB on 5, 6 and 9), on an Arduino Uno

// A night light that comes on when someone walks past.
//
//   HC-SR501 OUT -> pin 12   VCC -> 5V   GND -> GND
//   RGB LED red -> pin 5, green -> pin 6, blue -> pin 9, each through 220 ohm
//   the RGB LED's common cathode -> GND
//
// The HC-SR501 sees the warmth of a moving body. Its output goes HIGH when it
// sees movement and stays high for a few seconds after. The sketch lights the
// LED a warm white, waits 20 seconds, and only turns it off if nothing has
// moved in that time.
//
// Click the sensor's dome to walk past it.

const int PIR = 12;
const int RED_PIN = 5;
const int GREEN_PIN = 6;
const int BLUE_PIN = 9;
const unsigned long ON_MS = 20000;

bool lit = false;
unsigned long litAt = 0;

void color(int r, int g, int b) {
  analogWrite(RED_PIN, r);
  analogWrite(GREEN_PIN, g);
  analogWrite(BLUE_PIN, b);
}

void setup() {
  pinMode(PIR, INPUT);
  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);
  color(0, 0, 0);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: motion night light");
}

void loop() {
  bool moving = digitalRead(PIR) == HIGH;
  if (moving && !lit) {
    lit = true;
    litAt = millis();
    color(255, 180, 90);
    Serial.println("someone moved: light on");
  } else if (lit && millis() - litAt >= ON_MS) {
    if (moving) {
      litAt = millis();
      Serial.println("still moving: staying on");
    } else {
      lit = false;
      color(0, 0, 0);
      Serial.println("nobody there: light off");
    }
  }
  delay(50);
}