Ear splitter

If things are too quiet around your house, this Project will fix that in a hurry! Once you try this Project you'll know that it really lives up to its name.

When you finish wiring this Project, turn power ON. You'll immediately hear a loud, piercing tone (as will everyone else in the house!).

When you press the Key, you'll notice that the sound from the Speaker will become lower in tone — but still loud as ever, By pressing the Key in the right rhythm you can create sounds like a police siren or ambulance. The Project uses an audio oscillator circuit.

You'll find this to be a very common type of circuit in electronics — it's used in many projects. Why does the circuit change tone when the Key is pressed? Sorry - we're not going to tell you yet. But try following the wires from the Key to the other areas of the Parts. What do they connect to? (Okay, here's a hint: the Key adds another part in the circuit. Now try and find which part.)

Make a note of which part you think it is. Later on we'll see how sharp you were in figuring this circuit out...