I have seen a few Knock Sensors using the Piezo Speaker and the Arduino. I am wondering if there is a way to eliminate the Arduino and utilize a 555 Timer and other simpler components so that when the Piezo sensor detects a Knock it triggers a Relay to illuminate a light either in three successive pulses lasting 3 seconds or a continuous on time of 3 seconds then off again until the next Knock? ie: (Knock: Blink Blink Blink, or Knock Light on(3 seconds)off) I apologize, I have just started learning some of this.

  • \$\begingroup\$ Look up 555 or 556 one shot mode \$\endgroup\$
    – Passerby
    May 28, 2016 at 1:44

1 Answer 1


Use a 555 timer as a monostable with a 3 second timeout directly driving an LED, pull the 555's input up to Vcc, and trigger the 555 with a negative-going cap-coupled pulse generated by the piezo loudspeaker and amplified enough to drive the 555's trigger input to lower than Vcc/3.


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