Polaroid corporation was the first company to produce an autofocus camera. It was able to infer the distance of the subject by bouncing sound off of the subject and timing how long it took for the sound to bounce back from the subject. The longer it took, the further away the subject was. See the picture of their first autofocus product below:
See that gold disk above the lens? That was a giant speaker and microphone (formally called an "Ultrasonic Transducer") that could emit an ultrasonic "chirp" and could also detect when it bounced back. This is exactly the technique that mountain climbers use to determine how far away the next mountain is: they yell and time how long it takes for the echo to return.
Polaroid sold this transducer separately so experimenters like me could play with it and incorporate it into various products. The top picture of this post shows the first thing I did with it: I hooked it up to my HP 71 calculator and had it measure distances just by pressing a button. You can see the distance measurement in feet and inches in the calculator's display.
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| Measure for carpet by standing in the corner. Take two measurements and multiply them together. |
Another great application of this technology combines both high-fashion and security, and would probably sell a million if it were on the market. The Personal Space Invasion Alarm audibly warns passers-by that the user's space is being invaded, and is a must for Valley girls who travel abroad.
In practice, the transducer is worn around the neck as a piece of fashionable jewelry, while the relatively ugly driver components are hidden in the purse along with the 71. The 71 has been programmed to periodically fire the transducer, and will beep continuously as soon as anything comes within 1 1/2 feet of the user.
