In this ible I will show you how to build a circuit which responds to sound. Think sound activated switch, whistle keyrings or sonic screw driver. Ok, maybe it can't track alien life forms :( The circuit uses a microphone and band-pass filter to determine when a particular tone is heard. The circuit in this ible listens out for a whistling frequency, but it can be set up to listen to any tone, including ultrasound!!! The output of the circuit can be used to create a remote trigger for your camera, a mains relay to turn on the radio in the morning or a remote controlled car. I will show you how to do the bare minimum, and you can go off and make something awesome. Be sure to document and share your idea .

Turn off your hairdryers and lets get started!

Step 1: System Overview

This section gives you an overview of the circuit without all the nitty gritty. 

Sound Source
The sound source is the thing that produces an audible tone. In this instructable we will be using our mouths to whistle. If you are like me and suck at whistling you might like to use a mobile phone or computer to generate the tone. I will give you a couple of options later on.

The sound is picked up by the microphone and turned into an electrical signal.

Bandpass Filter
The electrical signal from the microphone contains all frequencies. The purpose of the bandpass filter is to filter out all the frequencies except for the frequency of interest - the whistle. 

In this ible we will be using an LED to indicate when circuit picks up a whistle. You can substitute this for a relay to turn things on and off.

No comments yet? <br> <br>LEAVE A COMMENT OF WHAT YOU WANT TO BUILD. I will select the coolest idea and send you the microphone breakout board and tone decoder. Be sure to label your comment with #soundidea. Only one winner will be selected, comments must be placed before 12am 10/09/13 NZST. <br> <br>
I was about to comment, jeeeez (haha). This is a very cool idea. I will have to think of some kind of thing I want to build incorporating these tools.
<p>I tried another microphone (sound module for arduino board) but it doesn't work on the LM567. any help? </p>
<p>is there a way to have a small range of frequency that passes through and have the current increase and decrease resistance in respect to the frequency range, then go into an LED? I just don't know much about electronics yet and I want to know if this is actually a thing before I try and make it work.</p>
<p>Instead of having a microphone could then plug your phone directly to the Band Pass Filter, with a Jack??</p>
I'm trying to make one that will be connected to an electric door lock and unlock and lock to the sonic screwdriver's sound, how do I make the microphone only respond to that sound?

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