light_servo.cpp

// Sketch for a servo that turns with the light intensity
// See video demo at https://youtu.be/BSZc9sFR4vs

#include <Servo.h>

const Servo myServo;
const int lightSensor = A0;
const int red = 7;
const int green = 8;
const int speaker = 6;
const int servo = 9;

const int lightsOnMs = 50;
const int lightSampleIntervalMs = 250;

void setup() {
  pinMode(red, OUTPUT);
  pinMode(green, OUTPUT);
  myServo.attach(servo);
}

int lastSensorValue = 0;

void loop() {
  const int sensorValue = analogRead(lightSensor);
  if (abs(sensorValue - lastSensorValue) > 3) { // Avoid reacting to tiny changes
    // Turn on green light if ascending, red light if descending
    digitalWrite(sensorValue > lastSensorValue ? green : red, HIGH);
    tone(speaker, map(sensorValue, 0, 1023, 20, 3000), 50);
    int angle = map(sensorValue, 0, 1023, 0, 178); // Too high makes the motor stay buzzing
    myServo.write(angle);
    lastSensorValue = sensorValue;
  }
  delay(lightsOnMs);
  digitalWrite(7, LOW);
  digitalWrite(8, LOW);
  delay(lightSampleIntervalMs - lightsOnMs);
}