#include <Servo.h>
Servo servo9; // Pin connected to servo mpo
const int piezo = A0; // Pin connected to piezo
const int switchPin = 2; // Pin connected to servo
const int yellowLed = 3; // Pin connected to yellow LED
const int greenLed = 4; // Pin connected to green LED
const int redLed = 5; // Pin connected to red LED
int knockVal; // Value for the knock strength
int switchVal;
const int quietKnock = 10; // Set min value that will be accepted
const int loudKnock = 100; // Set max value that will be accepted
boolean locked = false; // A true or false variable
int numberOfKnocks = 0; // Value for number of knocks
void setup() {
 servo9.attach(9);
 pinMode(yellowLed, OUTPUT); // Set LED pins as outputs
 pinMode(greenLed, OUTPUT);
 pinMode(redLed, OUTPUT);
 pinMode(switchPin, INPUT); // Set servo pin as input
 Serial.begin(9600);
 digitalWrite(greenLed, HIGH); // Green LED is lit when the 
 // sequence is correct
 servo9.write(0);
 Serial.println("The box is unlocked!");
}
void loop() {
 if (locked == false) {
 switchVal = digitalRead(switchPin);
 if (switchVal == HIGH) {
 locked = true;
 digitalWrite(greenLed, LOW);
 digitalWrite(redLed, HIGH);
 servo9.write(90);
 Serial.println("The box is locked!");
 delay(1000);
 }
 }
 if (locked == true) {
 knockVal = analogRead(piezo); // Knock value is read by analog pin
 if (numberOfKnocks < 3 && knockVal > 0) {
 if (checkForKnock(knockVal) == true) { // Check for correct 
 // number of knocks
 numberOfKnocks++;
 }
 Serial.print(3 - numberOfKnocks);
 Serial.println(" more knocks to go");
 }
 if (numberOfKnocks >= 3) { // If 3 valid knocks are detected, 
 // the servo moves
 locked = false;
 servo9.write(0);
 delay(20);
 digitalWrite(greenLed, HIGH);
 digitalWrite(redLed, LOW);
 Serial.println("The box is unlocked!");
 }
 }
}
boolean checkForKnock(int value) { // Checks knock value
 if (value > quietKnock && value < loudKnock) { // Value needs to be
 // between these
 digitalWrite(yellowLed, HIGH);
 delay(50);
 digitalWrite(yellowLed, LOW);
 Serial.print("Valid knock of value ");
 Serial.println(value);
 return true;
 }
 else { // If value is false then send this to the IDE serial
 Serial.print("Bad knock value ");
 Serial.println(value);
 return false;
 }
}