Clap your hands, "hear" comes Big-Ears! Our sound-activated mobile pet (buggy) will give hours of fun.

Sound travels in waves as it moves through the air at a speed of roughly one-third of a kilometer per second. Sound also has direction, so that a sound wave will strike one ear one three-thousandth of a second before it strikes the other - assuming, that is, that one is standing sideways to the sound source.

By electronic standards, this is very slow. Considering that many opamps (operational amplifiers) will detect differences of just millionths of a second, a simple electronic circuit will easily pick this up. Even if two electronic "ears" are mounted relatively close to each other (say two or three centimetres apart), a modern integrated circuit will readily detect that a sound passed one "ear" before the other.

The circuit described here takes advantage of these basic characteristics of sound, triggering a switch when one "ear" hears a sound before the other - and vice versa. This is specifically applied to the small mobile robot, which we have called the Big-Ears Buggy. This is capable of responding to sound from three directions, and of driving up to the source.

Although the "Big-Ears" Buggy is the application described here in detail, the circuit is potentially very diverse in application. Through the use of the two relays provided (RLA and RLB), there are many interesting possibilities - among them the following:

• Since it is a very human trait to be able to respond to the direction of sound, the circuit may be used to seemingly imbue objects with human characteristics. For instance, two small motors wired to a pulley arrangement behind a painting of Great-Granddad would make his eyes move in your direction when you speak.
• Similarly, an advertising board could move to face talking shoppers, or a head could turn in people’s direction.
• It could be used as a novel audio "snap" indicator, or as an audio "Who was first?" indicator, finally settling any arguments as to who spoke first!
• It could also serve as an aid for the deaf, giving a visual indication that a sound is coming from a particular direction.