knock example

[Wild_Bill]

I am starting on my second project using an UNO R3. The first state will use the knock function, but I could not get my sketch to work. I backtracked and loaded and ran just the knock example. I can not get a knock to register, I have varied the thresholdLOW value and still can not get a knock to register. If I remove the patch cable from A0, the serial monitor begins to repeatedly display "knock" without any input knock. "Knock" will continue to display until I reattach the patch cable to A0. I have doubled checked my wiring and it is correct. Could I have a bad piezo? I can not understand how the Uno thinks that there is a knock when there is no connection at A0.

[UKHeliBob]

No code posted
No schematic posted
No help possible

Please follow the advice on posting code given in posting code

[hammy]

Or how you are creating the “knock “ - suggest you tap the sensor fairly hard with a screwdriver

When I made one of these I had to use an op amp to amplify the signal , but as said information needed !

[Wild_Bill]

[code]
/*
  Knock Sensor

  This sketch reads a piezo element to detect a knocking sound.
  It reads an analog pin and compares the result to a set threshold.
  If the result is greater than the threshold, it writes "knock" to the serial
  port, and toggles the LED on pin 13.

  The circuit:
	- positive connection of the piezo attached to analog in 0
	- negative connection of the piezo attached to ground
	- 1 megohm resistor attached from analog in 0 to ground

  created 25 Mar 2007
  by David Cuartielles <http://www.0j0.org>
  modified 30 Aug 2011
  by Tom Igoe

  This example code is in the public domain.

  http://www.arduino.cc/en/Tutorial/Knock
*/


// these constants won't change:
const int ledPin = 13;      // LED connected to digital pin 13
const int knockSensor = A0; // the piezo is connected to analog pin 0
const int threshold = 100;  // threshold value to decide when the detected sound is a knock or not


// these variables will change:
int sensorReading = 0;      // variable to store the value read from the sensor pin
int ledState = LOW;         // variable used to store the last LED status, to toggle the light

void setup() {
  pinMode(ledPin, OUTPUT); // declare the ledPin as as OUTPUT
  Serial.begin(9600);       // use the serial port
}

void loop() {
  // read the sensor and store it in the variable sensorReading:
  sensorReading = analogRead(knockSensor);

  // if the sensor reading is greater than the threshold:
  if (sensorReading >= threshold) {
    // toggle the status of the ledPin:
    ledState = !ledState;
    // update the LED pin itself:
    digitalWrite(ledPin, ledState);
    // send the string "Knock!" back to the computer, followed by newline
    Serial.println("Knock!");
  }
  delay(100);  // delay to avoid overloading the serial port buffer
}

[/code]

[anon57585045]

Is your "piezo" a buzzer, or a passive disc?

[jimLee]

I've built knock sensors and found that you really need to grab some data over time. Then check min/max for amplitude of the knock. Amplitude is the key. (I think)

-jim lee

[anon57585045]

Actually, there is an example sketch that you can run that prints the analog values to serial. Please load and run that, and then post a cut and paste of the serial output from that. Then we can see what the raw data looks like.

[Wild_Bill]

aarg

This is the style piezo that I am using.

[Wild_Bill]

I mounted the piezo to a board with some relief holes for the mounting tabs so that the base of the piezo was completely touching the board and reset the threshold value to 5. Now with 4 or 5 solid knocks on the board, the serial monitor displays a single "knock". Knowing that my parts do work, I can resume working on my original sketch using a more elaborate knock function. Thanks for the suggestions.