Picture of 'Knock Back' - A Knock Echoing Arduino
This is a simple Arduino sketch that was originally designed to experiment with arrays and the built-in timing functionality. I based it on the tutorial sample code http://www.arduino.cc/en/Tutorial/Knock

The system consists of a piezo sensor connected to an analog pin that listens for a knock from the user. The Arduino then stores the time the knock occurred in an array. After a predefined time without further knocks occurring, the Arduino will 'play back' the knocks on a buzzer and LED in time to the original knocking pattern.

The device could be expanded to include a stepper motor or similar suitable output that would recreate the knocks exactly, just replace the output buzzer.
You could also use the piezo input sensor as the output buzzer by altering the code.

Step 1: Materials

Picture of Materials
You will need:

1. An Arduino UNO or compatible board.
2. An LED and appropriate resistor (I used 220R).
3. A piezo sensor.
4. A 1M pull-down resistor.
5. A piezo buzzer or alternative output device (see page one notes).
6. A breadboard and wires.
jjurotte1 year ago

Works great Dan. Well commented code too :-)

azharz2 years ago
Very nicely done.
dan_nicholson (author) 2 years ago
It's a SainSmart UNO (an arduino clone)
Ma77h3w2 years ago
what type of arduino is that?