Lamp inrush on an Arduino Uno

// Lamp inrush: an Uno switches a 6 V filament lamp with a MOSFET and measures
// its current through a 1 ohm resistor, a millisecond at a time, to catch
// the surge a cold filament draws.
//
//   lamp      6 V 0.3 A, from the + of four AA cells to the MOSFET's drain
//   MOSFET    IRLZ44N: gate -> pin 9, source -> A0 and 1 ohm to GND
//   cells     - to GND, shared with the Uno
//
// Tungsten's resistance climbs with its temperature, and a lamp's filament is
// about a twelfth of its hot resistance when it is cold. So for the first few
// milliseconds after it is switched on it draws several times its rated
// current, until it heats up and its resistance rises. That surge is why
// lamps usually fail at the moment they are switched on.
//
// The 1 ohm resistor turns the current into a voltage, a volt an amp, and
// one ADC count is 4.9 mA. Each cycle prints the peak of the first five
// readings (the surge),
// the reading 10 ms in, the running current, and how long it took to come
// within a tenth of it. A warm filament draws less: the cycles after the
// first start from a lamp that has not cooled all the way down.

const int GATE_PIN = 9;
const int SHUNT_PIN = A0;

long milliamps(int counts) {
  return (long)counts * 5000 / 1023;  // 1 ohm: a volt an amp
}

int samples[300];

void setup() {
  Serial.begin(9600);
  pinMode(GATE_PIN, OUTPUT);
  Serial.println("Lamp inrush: 6 V 0.3 A lamp, 1 ohm shunt");
}

void loop() {
  digitalWrite(GATE_PIN, HIGH);
  unsigned long start = millis();
  for (int i = 0; i < 300; i++) {
    while (millis() - start < (unsigned long)i) {
    }
    samples[i] = analogRead(SHUNT_PIN);
  }
  long running = milliamps(samples[299]);
  int settled = 299;
  while (settled > 0 && milliamps(samples[settled - 1]) * 10 <= running * 11) settled--;

  int peak = 0;
  for (int i = 0; i < 5; i++) peak = max(peak, samples[i]);

  Serial.print("inrush ");
  Serial.print(milliamps(peak));
  Serial.print(" mA, 10 ms ");
  Serial.print(milliamps(samples[10]));
  Serial.print(" mA, running ");
  Serial.print(running);
  Serial.print(" mA, settled in ");
  Serial.print(settled);
  Serial.println(" ms");

  delay(700);
  digitalWrite(GATE_PIN, LOW);
  delay(3000);
}