In this project I build a circuit with a Led and a piezo to function as a on and off a Led when it receives a number of knocking sounds within a given range.

## Step 1: Things You Need

Hardware

• LED
• Diode(Zener 5.1v).
• Piezo Buzzer
• 470Ω Resistor
• 1MΩ Resistor
• Arduino uno
• jumper wire

Software

• Arduino IDE

## Step 3: Schematics

The circuit is so simple:

Pin A2 --------------------------1MΩ-------------------Gnd

Pin A2 ------------------------Diode-------------------Gnd

Pin A2 ------------------Piezo Buzzer---------------Gnd

Pin 8 -------------------------470Ω-------Led 1------Gnd

Gnd-------------------------------------------------------Gnd

## Step 4: Arduino Sketch

"const int outputPin = 5; // led indicator connected to digital pin

const int knockSensor = A2; // the piezo is connected to an analog pin

const int thresholdHIGH =120; // threshold value to decide when the detected knock is hard (HIGH)

const int thresholdLOW = 70; // threshold value to decide when the detected knock is gentle (LOW)

const int secretKnockLength = 3; //How many knocks are in your secret knock /* This is the secret knock sequence * 0 represents a LOW or quiet knock * 1 represents a HIGH or loud knock * The sequence can be as long as you like, but longer codes increase the difficulty of matching */

const int secretKnock[secretKnockLength] = {0, 0, 1}; int secretCounter = 0; //this tracks the correct knocks and allows you to move through the sequence

int sensorReading = 0; // variable to store the value read from the sensor pin void setup() { //Set the output pin as an OUTPUT pinMode(outputPin, OUTPUT); //Begin Serial Communication. Serial.begin(9600); } void loop() { // read the piezo sensor and store the value in the variable sensorReading: sensorReading = analogRead(knockSensor); // First determine is knock if Hard (HIGH) or Gentle (LOW) //Hard knock (HIGH) is detected if (sensorReading >= thresholdHIGH) { //Check to see if a Hard Knock matches the Secret Knock in the correct sequence. if (secretKnock[secretCounter] == 1) { //The Knock was correct, iterate the counter. secretCounter++; Serial.println("Correct"); } else { //The Knock was incorrect, reset the counter secretCounter = 0; Serial.println("Fail"); digitalWrite(outputPin, LOW); }//close if //Allow some time to pass before sampling again to ensure a clear signal. delay(100); //Gentle knock (LOW) is detected } else if (sensorReading >= thresholdLOW) { //Check to see if a Gentle Knock matches the Secret Knock in the correct sequence. if (secretKnock[secretCounter] == 0) { //The Knock was correct, iterate the counter. secretCounter++; Serial.println("Correct"); } else { //The Knock was incorrect, reset the counter. secretCounter = 0; Serial.println("Fail"); }//close if //Allow some time to pass before sampling again to ensure a clear signal. delay(100); }//close if else //Check for successful entry of the code, by seeing if the entire array has been walked through. if (secretCounter == (secretKnockLength) ) { Serial.println("Welcome"); //if the sececret knock is correct, illuminate the LED for a couple seconds digitalWrite(outputPin, HIGH); //Reset the secret counter to 0. secretCounter = 0; }//close success check }//close loop".

This is great! FYI the video doesn't work on the current version of the Instructables Android ap unless you link to it. So I can't see the video.
<p>Ok, I inserted a linck to youtube</p>