Dinosaur game player: light sensor on A0, servo on 9, on an Arduino Uno

// A robot that plays the dinosaur game.
//
//   photoresistor: one leg -> A0, the other -> GND; 10k from A0 -> 5V
//   servo signal -> pin 9   red -> 5V   brown -> GND
//
// On the bench the light sensor is taped to the screen just ahead of the
// dinosaur, and the servo's arm rests over the space bar. The game's
// background is bright; a cactus is dark. With the 10k pulling A0 up and the
// photoresistor pulling it down, a bright screen gives the sensor a low
// resistance and A0 a low reading, and a dark cactus a high one. When the
// reading rises past THRESHOLD, the servo swings down to press the key.
//
// Drag the light level on the photoresistor down to play the cactus.

#include <Servo.h>

const int SERVO_PIN = 9;
const int SENSOR_PIN = A0;
const int THRESHOLD = 310;  // tune this to your screen's brightness
const int REST = 0;
const int PRESS = 30;

Servo arm;

void setup() {
  arm.attach(SERVO_PIN);
  arm.write(REST);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: dinosaur game player, light sensor on A0, servo on 9");
}

void loop() {
  int light = analogRead(SENSOR_PIN);
  Serial.println(light);
  if (light > THRESHOLD) {
    Serial.println("cactus! jump");
    arm.write(PRESS);
    delay(200);
    arm.write(REST);
    delay(300);
  }
  delay(20);
}