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.
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.