Turn off your hairdryers and lets get started!
Step 1: System Overview
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.
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.