A simple knock sensor example


In the following example I used a piezo element (as the knock sensor) connected to analog pin 0 with the negative wire connected to ground. Then I placed a 1M resistor between the pin 0 and ground connection.

    /* Knock Sensor

     * ----------------

     *

     * Program using a Piezo element as if it was a knock sensor.

     *

     * We have to basically listen to an analog pin and detect 

     * if the signal goes over a certain threshold. It writes

     * "knock" to the serial port if the Threshold is crossed,

     * and toggles the LED on pin 13.

     *

     * (cleft) 2005 D. Cuartielles for K3

     * edited by Scott Fitzgerald 14 April 2013

     */



    int ledPin = 13;

    int knockSensor = 0;               

    byte val = 0;

    int statePin = LOW;

    int THRESHOLD = 8;



    void setup() {

     pinMode(ledPin, OUTPUT); 

     //Serial.begin(9600);

    }



    void loop() {

      val = analogRead(knockSensor);     
      //Serial.println(val);
      if (val >= THRESHOLD) {

        statePin = !statePin;

        digitalWrite(ledPin, HIGH);
        delay(10);
        digitalWrite(ledPin, LOW);

        //Serial.println("Knock!");



      }

      //delay(100);  // we have to make a delay to avoid overloading the serial port

    }

I commented out the Serial communication statements because it made the sensor setup less responsive. Initially the threshold value was set to 100, however I found setting the value to 5 made it a lot more sensitive.

Output:

Here's a quick video of the knock sensor in action:

!v[](http://www.jamesrobertson.eu/r/videos/2016/mar/06/piezo-elements-knock-sensor.ogv)

## Resources

* Arduino - KnockSensor https://www.arduino.cc/en/Tutorial/KnockSensor
* 'Knock Back' - A Knock Echoing Arduino http://www.instructables.com/id/Knock-Back-A-Knock-Echoing-Arduino/?ALLSTEPS
* Arduino - Knock https://www.arduino.cc/en/Tutorial/Knock
* 5x Piezo Element Pickup Drum Trigger Transducer 20mm http://www.jamesrobertson.eu/pages/2014/aug/23/p230814t2101.html

knock sensor knocksensor vibrations piezoelement