Workbench light on an Arduino Uno

// Workbench light: a 3 W power LED spot that pin 8 switches through a D4184
// MOSFET module.
//
//   8       the module's TRIG (on and off)
//   GND     the module's GND, shared with the Uno (its GND is its VIN-)
//   12 V    a 12 V 2 A adapter into the module's VIN+ and VIN-
//   spot    the module's OUT+ through a 12 ohm 10 W resistor to the star's +,
//           its - on the module's OUT-
//
// A 3 W LED has no resistor of its own. It is rated 700 mA at about 3.4 V,
// so the 12 ohm one sets the current: (12 - 3.4) / 12 = 0.72 A, and it burns
// (12 - 3.4) x 0.72 = 6.2 W, which is why it is a 10 W part. Leave it out and
// the LED takes amps and is gone in a second; a constant-current driver would
// waste less, but the resistor is the honest start.
//
// Press Run: the spot flashes on for two seconds in four.

const int SPOT_PIN = 8;

void setup() {
  Serial.begin(115200);
  Serial.println("Mokxi Arduino Uno: workbench light");
  pinMode(SPOT_PIN, OUTPUT);
}

unsigned long lastSpot = 0;
bool spot = false;

void loop() {
  unsigned long now = millis();
  if (now - lastSpot >= 2000) {
    lastSpot = now;
    spot = !spot;
    digitalWrite(SPOT_PIN, spot ? HIGH : LOW);
    Serial.println(spot ? "spot on" : "spot off");
  }
}